Research ArticleFretting Wear Behavior and Damage Mechanisms ofInconel X-750 Alloy in Dry Contacts

Ibrohim A Rustamov 1 Ozoda Sh Sabirova2 Zixi Wang 1 and Yuming Wang1

1State Key Laboratory of Tribology Tsinghua University Beijing 100084 China2Department of Mechanical Engineering Tashkent State Technical University Tashkent 100095 Uzbekistan

Correspondence should be addressed to Zixi Wang zxwangmailtsinghuaeducn

Received 10 November 2018 Revised 19 January 2019 Accepted 12 February 2019 Published 4 March 2019

Academic Editor Hongtao Zhu

Copyright copy 2019 Ibrohim A Rustamov et al is is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Tribological behavior of the Inconel X-750 alloy disk subjected to fretting against the GCr15 steel ball was investigated in anambient laboratory air with relative humidity of 55ndash65 A high-frequency oscillating Optimol SRV 4 tribometer was employed toexecute dry fretting tests in the partial and gross slip regimes under constant 100N normal load Tests were carried out for 10 30and 90minutes and the friction forces vs displacement amplitudes were monitored during the test duration Posttest exam-inations were conducted utilizing advanced tools such as 3D optical surface profiler scanning electron microscopy (SEM) andenergy dispersive X-ray spectroscopy (EDX) e main objective was to obtain wear scar evolutions frictional properties anddegradation mechanisms under the different running conditions over time It was found that fretting wear behaviors of frictionpairs were strongly influenced by fretting regimes Degradation evolutions were greatly influenced by fretting time during partialslip regimes ie evolving from asperity deformation and slight damage to the fatigue crack and material transfer However thecombination of adhesive abrasive delamination and wear oxidation mechanisms was repeated during the entire gross slipfretting process

1 Introduction

e definition of fretting is given as a complex wear phe-nomenon between contacting surfaces subjected to relativevibratory movements with a small amplitude at high fre-quencies [1] as other authors offered the definition ofldquofretting is a relative cyclic motion between two surfaceshaving a nonuniform distribution of local relative displace-ment at their contactrdquo [2] Based on the published experi-mental data fretting regimes are broken into three differentsliding forms namely stick partial slip and gross slip whichcontrols the contact interface as long as the fretting processmakes the transition to the reciprocating motion [3] edistribution of local relative displacement refers to the al-terations of the sliding conditions over the contact interfaceie zero relative displacement during stick small slip in theperiphery and zero displacement in the sticking portionduring partial slip and more uniformly distributed relative

displacement in the entire contact during gross slip Fur-thermore taking the imposed displacement into accountfretting conditions between two convex pairs or ball-on-flatcontacts were described by Mindlinrsquos elastic model in re-lation to two shear models [4] In small displacements thecorresponding tangential force Ft is smaller than the criticaltotal sliding shear force and as a result contact is in partialslip with the central stick region and a ring-shaped annuluswhere sliding occurs As the displacement amplitude in-creases the tangential force reaches the critical total slidingvalue therefore the stick region in the contact center dis-appears gradually and gross slip occupies the whole contactinterface is trend can be described by the relation ofFtgt microP where P is the applied normal force and micro is thefriction coefficient

Fretting maps which are proposed by Vingsbo andSoderberg [3] and developed by Zhou and Vincent [5] areused nowadays to represent the fretting regimes and

HindawiAdvances in Materials Science and EngineeringVolume 2019 Article ID 7079819 15 pageshttpsdoiorg10115520197079819

damages based on the normal load and the displacementamplitude (Figure 1(a)) e relationship between tangentialforce and imposed displacement amplitude the so-calledldquofretting looprdquo was closed elliptical and parallelogramduring stick partial slip and gross slip conditions re-spectively Besides Varenberg et al [2] introduced a newterminology ldquoslip indexrdquo to identify all the different frettingregimes e dimensionless slip index is obtained from afretting loop which is shown schematically in Figure 1(b)e slip amplitude As is a function of all the independentgoverning parameters such as the imposed displacementamplitude Ad the normal load P and the elastic slope offretting loop Sc According to their study fretting existswhen δ lt 10 Partial slip is present in δ values between 05 and06 while gross slip prevails in the range of 08 and 10Beyond this range reciprocal sliding occurs (δ gt 11) eenclosed area by fretting loop corresponds to the dissipatedenergy Ed which is related to the wear produced during aparticular fretting time [6 7]

e fretting wear behavior of materials is also a verycomplicated phenomenon in which different damagemechanisms (adhesion plastic deformation abrasion fa-tigue crack delamination and oxidation) and factors(contact geometries material properties and environmentalconditions) are involved [8 9] Depending on the runningconditions the material responses can be deformed asperityadhesion in the stick crack initiation and propagation in thepartial slip regime (PSR) and loss of material by wear in thegross slip regime (GSR) [10 11] e material removal isusually very slow process in well-designed tribologicalsystems however it is very steady and continuous Contactsurfaces subjected to fretting have a specific appearance withred-brown patches on ferrous metals as a result of lapping bymetallic oxide debris [12] It is also noticed that the wear ofsurfaces that undergo fretting is strongly affected by theenvironment ie the amount of fretting wear in humid air issubstantially greater than that observed in dry air [13]

In the last decade most of the fretting wear experimentshave been conducted on the nickel-based nuclear engi-neering materials such as Inconel 600 690 and 690TTalloys which are known for their corrosion and oxidationresistance in the elevated temperatures [14ndash19] e effectsof different fretting parameters (eg sliding amplitudenormal load and temperature) and material properties(eg heat treatment precipitated carbides grain sizehardness and microstructural characterizations) were in-vestigated in their study to evaluate different degradationmechanisms and fretting behaviors As far as these factorsmake fretting a system property the complexity of thecontact interactions should be clarified by precise align-ments of the specimens and proper laboratory environmentIn this work suitable laboratory experiment was set to in-vestigate the tribological properties of Inconel X-750 alloyunder both partial and gross slip conditions in dry ball-on-flat contact configuration Inconel X-750 is a precipitation-hardenable nickel-chromium based super alloy where it iswidely used in gas turbines pressure vessels rocket enginesnuclear reactors tooling and aircraft structures [20] Itsoutstanding relaxation resistance is beneficial for high-

temperature springs and bolts Besides it has good re-sistance to corrosion and oxidation as well as high tensileand creep-rupture properties at elevated temperatures after asuitable heat treatment [21] Limited experimental works areperformed concerning about its mechanical properties indifferent temperature environments [22] but no literatureincludes the fretting wear behaviors of Inconel X-750 alloyus the specific objectives of the present study wouldcontribute to a better knowledge of the tribological natureand surface degradation evolutions of Inconel X-750 alloyduring fretting wear process

2 Experimental Setup

Ball-on-flat fretting experiments were run at room tem-perature of 20ndash25degC using the SRV 4 (Optimol InstrumentsGermany) high-frequency oscillation system with 50ndash60air humidity in dry condition e test rig is equipped with asoundproof chamber integrated electronic measurementsload cell oscillating rods and other modules to controlfretting parameters as shown in Figure 2 e lower InconelX-750 (solution annealed at 980degC for 2 h) disk specimenwith 24mm diametertimes 78mm height was fixed by clampsand subjected to the fretting by upper oscillating GCr15(Chinese GB 308ndash89) steel ball with diameter of 10mm androughness of 0025 microm (Ra) Table 1 shows the chemicalcompositions for both of the friction materials Modulus ofelasticity and Poissonrsquos ratio are 214GPa and 029 for X-750alloy and 210GPa and 03 for GCr15 ball respectivelyVickers hardness tests were performed by Qness (Austria)with the 20 microm diameter pyramidal diamond tip and 296HV was obtained for Inconel X-750 alloy while 758 HVmeasured for GCr15 ball Lower specimens were machinedaccording to the test rig specifications and grounded withwaterproof SiC abrasive papers (grain size 5 microm) sub-sequently polished with water based polycrystalline di-amond paste (particle size 1 microm) to have a mirror finishPrior to the test ball and disk specimens were cleaned in anultrasonic acetone bath for 20minutes and dried withcompressed blowing air

Once the specimens were ready fretting parameters wereinput via integrated computer software of the fretting weardevice Imposed displacement amplitudes were set to 40 micromand 100 microm under the constant 100N normal load ecalculated initial Hertz contact stress was 2185MPa andcontact radius was 296 microm Linear speed of the oscillatingball was 8mms for all cases which produces differentfrequencies for different displacement amplitudes 50Hz at40 microm and 20Hz at 100 microm Test durations were 10 30 and90minutes which also produces different number of frettingcycles for both stroke lengths Each test was repeated at leasttwice to confirm the consistency of fretting wear resultsFretting parameters are listed in Table 2

Monitoring the contact responses during fretting is oneof the vital requirements to characterize the fretting processe basic variables such as displacement amplitude andfriction coefficient as the ratio of tangential force to normalforce (FtP) were simultaneously recorded as a function oftime by the computer-based data acquisition system Both

2 Advances in Materials Science and Engineering

quantities also can be displayed as a force-displacement (Ft-D) hysteresis loop or fretting loop which is recorded byfriction signal analysis module (FSA) for every frettingcycles Moreover slip regimes were also conrmed by theuniversal slip index δ criterion which was mentioned above

After the samples were collected from fretting tests theywere ultrasonically cleaned again with acetone to removeloose debris from wear scar and postexperimental analyseswere carried out to investigate wear volumes and surfacemorphologies Surface topography information was ob-tained by employing the noncontact 3D optical proler(Zygo Nexview AMETEK Inc USA) to measure the wearvolume under the at surface prole and to generate in-teractive 3D plots as well as cross-section proles of thewear scar In order to have a high-quality morphologyanalysis the worn surfaces were coated with platinum (Pt) in842 nm thickness with 011 nms sputter rate for 75 secondsScanning electron microscopy (SEM) investigations wereconducted by TESCAN LYRA3 (Czech Republic) in

23eminus 2 Pa vacuum chamber pressure and electron beamwith 20 kV to reveal the degradation mechanisms on theworn surface during dierent fretting regimes Oxide con-tents and other chemical compositions on the worn surfaceswere detected by using the energy-dispersive X-ray spec-troscopy (EDX) embedded analyzer

Table 1 Chemical compositions for the frictional pairs (wt)

MaterialsElements

Ni Cr Fe Ti Al Nb+Ta Mn Si S Cu C CoInconel X-750 716 145 58 26 05 083 062 02 001 001 003 001GCr15 03 146 Bal mdash mdash mdash 036 019 0025 006 096 mdash

No damage Crack WearStick PSR GSR

Reci

proc

al sl

idin

g

Nor

mal

forc

e

Displacement amplitude

(a)

2As

2Ad

Slip ratio s = AsAd

Slip index δ = AdScP

Ft

D s = 1 ndash 12δ

Partial slip 05 le δ lt 06Gross slip 08 lt δ lt 10

Reciprocal sliding δ gt 11

Ed

Sc

(b)

Figure 1 Fretting map for fretting regimes and material response (a) and fretting loop by tangential force vs displacement amplitude (b)(reproduced from Reference [2])

Loading system

Oscillating rod

X-750 alloydisk

GCr15steel ball

Oscillating rod

Piezotransducer Heating cartridge

1cm

Figure 2 SRV 4 fretting wear test device

Table 2 Fretting test parameters

Parameters ValuesNormal load 100NDisplacement amplitude 40 microm 100 micromFrequency 50Hz 20Hz

Number of cycles30000 1200090000 36000270000 108000

Linear speed 8mmsTotal distance 48m 144m 432mRelative humidity 50ndash60

Advances in Materials Science and Engineering 3

3 Results

31 Wear Characteristics e SEM images of wear scars onthe lower specimens and superimposed cross-section pro-files perpendicular to the fretting direction are shown inFigures 3 and 4 for different amplitudes through the frettingtime respectively As can be seen the worn surfaces were ina circular shape for both displacement amplitudes but with aslight elongation in the direction of fretting for the initialstages of 100 microm amplitude e fretted surfaces were roughall over and as the displacement amplitude increases thesize of the worn surface was significantly increased over time(width from 1250 microm to 1750 microm) which indicates fullsliding in the whole contact area In contrast in the case of40 microm the shape of the wear scars was remaining almostsame for all fretting tests and very similar to Mindlinrsquosdefinition in which the central stick region was formedbecause of higher contact stresses in the center while theslight slip was observed in the periphery of the contact due tostick-slip effect [4]

e stick region which was 150 microm in radius (smallerthan Hertzian contact radius of 296 microm) after 10minutes offretting became narrower twice as much after 90minutes offretting test covered with cracks by the effect of repetitivecyclic stresses

It is obvious in Figure 4 that the wear scars for 100 micromwere wider and deeper than 40 microm In the initial phases offretting the cross-section profiles in PSR demonstratedconcave pit due to higher contact pressure while a bulk ofmaterials was transferred to the contact borders in GSR dueto plastic deformation Later in Figure 4(c) the wear scarsevolved to ldquoWrdquo shape cross section after 90minutes offretting for both PSR and GSR For gross slip conditions thiscan be explained with the load-carrying wear debris layerwhich was mostly generated in the contact annulus ratherthan in contact center thus bearing contact pressures near tothe contact border [10] On the other hand some asperitieswere popped up at the contact center in PSR while theperipheral contact region was smooth due to the microslipoccurrence It was evaluated through fretting experimentsthat the wider asperity areas were observed in the contactcenter with the smaller imposed displacement amplitudesand the greater normal loads [23]

3D surface mapping and noncontacting wear volumeand worn area measurements were obtained by 3D opticalsurface profiler as illustrated in Figure 5 is process takesthe initial step of capturing the millions of data points in thewear scar region with high-precision objective lenses fol-lowed by the selection of worn area to calculate the wearvolume under the original flat surface as depicted inFigures 5(b) and 5(c) Figure 6 gives the information ofcalculated wear volume worn area and wear rate as afunction of time for both imposed displacement amplitudesWear volumes and worn surface areas have grown dra-matically at 100 microm displacement amplitude (ie 37times

106 microm3 and 94times104 microm2 after 10min and 134times106 microm3

and 226times104 microm2 after 90min respectively) while theprogress of wear volume and scar area was very small at40 microm displacement amplitude almost negligible values of

065 to 084times106 microm3 and 3 to 34times104 microm2 after 10min and90min respectively

e wear rate which is defined to be the volume ofmaterial removed per unit sliding distance WVs wasdecreasing gradually during fretting process for both im-posed displacement amplitudes as shown in Figure 6(c)is process is usually attributed to the running-in orbreaking-in effects in the initial fretting periods where theinitial wear rate is higher and slowly lowers while thecontacting surfaces evolve to their steady-state of wear [24]Besides for steel sliding in air the rise in temperature fromfrictional heating promotes surface oxidation Conse-quently the wear rate decreases due to the oxide film for-mation which provides a protective layer against furtherwear [25 26]

32 Coefficient of Friction Friction between two countersurfaces was due to the various combined effects of adhesionand abrasion by wear particles and hard asperities de-formations e degree of friction is expressed as a co-efficient of friction (micro) which is the ratio of tangential force(Ft) to the normal load (P) and shown in Figure 7 as afunction of time For both imposed displacement ampli-tudes rapid growth in COF was observed in the beginning offretting test in a few seconds almost jumping to 08 value At40 microm displacement amplitude the contact is subjected topartial slip with junction of adhesion and sliding zones thusthe tangential force remains less than the product of appliednormal load and the static friction coefficient is tendencyis described by Ftlt microP and COF continued in a steady pacefor the rest of the test But at 100 microm coefficient of frictionwas decreasing suddenly dropping to 07 for a few tenseconds followed by gradual increase to the value of 09 afterabout 400 s and kept at steady-state level As far as largerrelative motion is concerned this initial rapid rise in COF isbelieved to be due to the rupture of the ldquowork-hardeningrdquo orcontaminant layer of the surface [16 18] e highest wearrate would also be possibly associated with the mass elim-ination of the contact surface in this period of fretting

In this experiment the friction signal was sinusoidalduring the entire test without break as portrayed in Figure 8e variation of coefficient of friction is plotted during the600th second for both imposed amplitudes In Figure 8(a) apure periodic sine wave was observed in the case of PSRwhen the amplitude was 40 microm because the frictional forcein the contact interface as a reaction to the imposed am-plitude was not enough to cause a full slide In Figure 8(b)the curve of coefficient of friction at 100 microm was formed as asine wave with clipped peaks which indicates the full slidebetween frictional pairs

33 Fretting Loop In most of the theoretical and experi-mental works the decisions of fretting regime and degra-dation mechanisms are made based on the ldquofretting looprdquowhich is defined by ldquoforce-displacementrdquo curve [3 5 6 9ndash12]Figure 9 shows the comparative Ft-D curves for partial andgross slip at the onset (after 5min) and the end (after 90min)of the fretting test e partially closed and elliptical curve

4 Advances in Materials Science and Engineering

which corresponds to PSR was obtained for 40 microm inFigure 9(a) However due to the continuation of cyclic loadsthe central mechanical interlocking was reduced and theclosed part of the loop was slightly widened after 90minis situation is related to the transition from primary elasticto plastic shear form and also due to the limited relative slipand small surface modification at higher normal loadParallelogram Ft-D curves at 100 microm attributed to GSRwhere displacement amplitude and thus the area of dissi-pated energy in the contact interface were greater In thiscase full sliding prevailed in the whole contact interfaceresulting in a higher rate of particle detachment and relativemotions were predominantly accommodated by plasticdeformation of counter surfaces during the entire fretting

processe fretting loop was kept almost unchanged for therest of the tests Besides fretting regimes according to theslip index criterion were also confirmed which can be cal-culated as shown in Figure 1(b) and δ found to be 056 forPSR while δ 106 for GSR both cases satisfying thetransition restrictions for slip index

34 Worn Scar Morphology e consequences of thesementioned frictional effects on the Inconel X-750 alloy andGCr15 steel ball specimens were investigated for partial andgross slip conditions by observing SEM morphologiesFigure 10 shows the damage evolutions on the flat material atthe stick and slip domains when the displacement amplitude

D = 40microm D = 100microm

(a)

D = 40microm D = 100microm

(b)

D = 40microm D = 100microm

(c)

Figure 3 SEM images of worn scars on Inconel X-750 alloy after (a) 10 (b) 30 and (c) 90minutes of fretting tests Double arrow indicatesfretting direction

Advances in Materials Science and Engineering 5

at 40 microm It was found that PSR was dominant in the contactarea with the mechanical interlocking of the asperities in thecontact center and adhered fretting scars due to themicroslips in the contact annulus However the degree ofthese degradation mechanisms was changing over thenumber of fretting cycles For instance Figure 10(a) showsthe fretting scars after 10min with limited material damagethe stick domain was smooth and surrounded by tiny pitsdue to the ratcheting eect In the later stages of frettingcycles (9times104) manymicrocracks surrounded the shrinkingstick area while the long crack perpendicular to the frettingdirection appeared in the contact border which looks like inthe stage of delamination process (Figure 10(b)) Further-more the sign of thick layer of material removal by harderGCr15 ball was observed in the slip region copye contactcenter was slowly worn out during the further fretting test by

overstressing and the wear mode was completely changedafter a considerable number of cycles (27times105) as shown inFigure 10(c) where the stick domain was totally rough andcovered with radial microcracks which were induced byfretting fatigue On the other hand the longer crack wasdetected along the far end of the contact which was partiallylled with wear debriscopye slip region also has been changedsince the previous condition where some layer of the an-nulus was transferred by opposite surface and this time theremaining layers of the contact annulus was removed byfurther cyclic stress which was assumed to be the exhaustionof ductility due to the plasticity accumulation by ratcheting

SEM morphologies in Figure 11 shows that the wholecontact interface was in full slide at 100 microm and degradationmechanisms were associated with adhesion abrasion de-lamination oxidation and plastic deformation as well as

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

μm

μm

0

5

10

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

(a)

μm

μm

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

ndash25

ndash30

ndash20

ndash15

ndash10

ndash5

0

5

10

(b)

μm

μm

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

5

10

(c)

Figure 4 Superimposed cross-section proles of wear scars perpendicular to the fretting direction through fretting time (a) After10minutes (b) After 30minutes (c) After 90minutes

6 Advances in Materials Science and Engineering

third-body flow between contact surfaces Red-brown oxi-dized powders were ejected from contact surfaces during thefretting process which can serve as abrasive particles prior totheir expulsion For example Figure 11(a) shows the wearmode onset of the fretting process in the contact centerwhere plowing grooves parallel to the sliding direction was

formed due to the larger relative motion by abrasive par-ticles followed by plastic shearing so that thick layers ofX-750 alloy were peeled off by adhesion Adhesive wear isoften occurred at the onset of fretting when friction pairscome into contact followed by plastic shearing that plucksoff the ends of the softer asperities is phenomenon is also

(a)

(b)

(c)

Figure 5 Surface topographies of worn scars for (a) 40 microm (left) and 100 microm (right) after 90minutes of fretting test (b) correspondingpreprocessed input area and (c) selected worn area to calculate the wear volume

Advances in Materials Science and Engineering 7

150

125

100W

ear v

olum

e los

s (lowast

106 micro

m3 )

75

50

25

0040

Displacement amplitude (microm)100

Aer 10 minutesAer 30 minutesAer 90 minutes

(a)

24

21

18

15

12

9

6

3

0

Wor

n sc

ar ar

ea (lowast

104 micro

m2 )

Displacement amplitude (microm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(b)

900

750

600

450

300

150

0

Wea

r rat

e (μm

3 mm

)

Displacement amplitude (μm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(c)

Figure 6 Calculated wear volumes (a) worn scar areas (b) and wear rates (c) after dierent time of fretting

00

02

04

06

08

10

12

0 600 1200 1800 2400 3000Time (s)

Coeffi

cien

t of f

rictio

n

3600 4200 4800 5400

40 microm100 microm

Figure 7 Coeordfcient of friction for contact pairs as a function of time

8 Advances in Materials Science and Engineering

attributed to galling and scuordfng [13] Figure 11(b) shows themagnied image in Figure 11(a) that the crack propagationswere prevented by particle detachment and started to spall

eventually becoming loose wear debris Fretted surfaces wererough owing to the plastic deformation and ploughing ef-fects and in some cases surface roughening would provide

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(a)

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(b)

Figure 9 Evolution of fretting loops for 40 microm and 100 microm after (a) 5 and (b) 90minutes of fretting

125100075050025000

ndash025ndash050ndash075ndash100ndash125

60001 60002 60003Time (s)

Coef

ficie

nt o

f fric

tion

60004 60005

40microm

(a)

Time (s)

125100075050025000

ndash025ndash050ndash075ndash100ndash125

Coef

ficie

nt o

f fric

tion

100microm

60001 60002 60003 60004 60005

(b)

Figure 8 Sinusoidal coeordfcient of frictions during 600 s fretting time for (a) 40 microm and (b) 100 microm

Advances in Materials Science and Engineering 9

escape channels for wear debris As the fretting test con-tinued the contact interfaces were slowly accommodated bythe plastic flow and further loading promoted the growth ofsubsurface cracks that parallel to the surface When thesecracks finally extended out to the free surface thin platelet-like wear particles delaminated as shown in Figures 11(c)and 11(d) In the same time when the delamination wasoccurring mostly in the contact center plastic flow of thecontacting surfaces in the periphery and third-body flowclose to the contact border were observed in Figures 11(e)and 11(f) respectively Moreover as temperature increasesbecause of frictional heating during GSR oxidation of thewear particles becomes more ubiquitous and as a

consequence thicker more continuous oxide layer will begenerated e greater contact temperature at this conditionalso causes plastic flow of the oxide film leading to moresevere oxidational wear [19]

Figure 12 shows the SEM images of wear scars andcorresponding 3D surface topographies of the steel ballsoscillated at 40 microm and 100 microm after 90minutes of frettingBoth wear scars were in a circular shape e worn surfacearea which was oscillated at 40 microm also contains the stickdomain in the contact center and slip domain at the pe-riphery as shown in Figure 12(a) However it is clear fromthe picture that a bulk of oxidized X-750 alloy surface layerin black was adhered to the half annulus of the contact which

Slip region

Stick region

Micropitboundary

Slip region

Adhesive microslip

(a)

Stick region

Microcracks

Slip region

Adhesive layerremoval

Crack delamination

(b)

Stick region

Cracks

Slip region

New crack growth alongthe contact border

(c)

Figure 10 SEMmicrographs of Inconel X-750 wear scars during PSR (a) after 10minutes (b) after 30minutes and (c) after 90minutes offretting Displacement amplitude is 40 microm Double arrows represent fretting direction

10 Advances in Materials Science and Engineering

was believed to be plucked off by harder GCr15 ball surfaceduring fretting induced by fatigue According to the wearscar in Figure 12(b) GSR was dominant at 100 microm with thesign of abrasion and small amount of transferred materialson the worn surface Figure 13 shows the EDX spectruminformation for the marked spots in Figure 12 on the wearscar areas Oxide content was very low (146 wt) in thestick region due to the constriction of the relative motionwhile microslip region was reacting with the oxygen in asmall amount On the other hand the highly concentratedoxygen content (29 wt) was detected on the transferredflat material in Figure 13(c) However the oxidation process

on the worn steel surface was faster during GSR rather thanPSR (Figure 13(d))

4 Discussion

e fretting wear process in an ambient temperature is oftendetermined by the contact geometry the oxidation processand the subsequent third-body behavior in the contact in-terface which significantly affect the friction and wearproperties in dry air [11 16 27] Wear properties such asvolume scar area and depth were considerably lowerduring PSR than GSR as shown in Figures 3ndash6 because of

(b)

Adhesive shear

Plowing

(a)

Crack spalling

(b)

Delamination

(c)

Delamination

Oxide layers

(d)

Plastic flow

(e)

Oxidized third-body flow

(f )

Figure 11 SEMmicrographs of Inconel X-750 wear scars during GSR (a) mixed abrasive and adhesive wear at the onset of fretting process(b) spalling of cracks (c d) delamination (e) plastic flow and (f) third-body flow near contact border Displacement amplitude is 100 micromDouble arrows represent fretting direction

Advances in Materials Science and Engineering 11

the small imposed contact area compared to the scale of thenormal load applied Yet the wear rate was maximum in therunning-in period for both cases decreasing gradually withfretting time in Figure 6(c) typically due to the formation ofthe oxide layer (also ldquoglazerdquo layer) on the worn surface which

can enhance the load-carrying capacity avoiding furtherwear [28] During the partial and gross slip conditions thefriction is the outcome of the direct interlocking of thesurface asperities and the trapped oxide debris behavior inthe contact interface respectively In Figure 7 the COF

Highly oxidized Inconel X-750alloy wear layer transfer

a b c

(a)

d

Oxidization

(b)

Figure 12 SEM morphologies of GCr15 steel ball worn scars oscillating at (a) 40 microm and (b) 100 microm Fretting time is 90minutes Doublearrows represent fretting direction

C

O

Fe

Ni SiPt CrMn

Fe

Ni

O KCr KFe KNi K

Element0653wt

019687490056

1888at

017572460044

00

06

12

17

23

29

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(a)

CO

Fe

NiSiPt Cr Mn

Fe

Ni

O KCr KFe KNi K

Element0146wt

026391270104

0470at

026184190091

200 300 400 500 600 700 800 900 10100Energy (keV)

00

05

10

16

21

26

KCnt

(b)

O KCr KFe KNi K

Element2959wt

107305115105

5793at

064702732863

C

O

FeNi SiPt

Cr

Mn Fe

Ni

00

06

12

18

24

30

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(c)

O KCr KFe KNi K

Element1499wt

020378570071

3572at

014953640046

C

O

FeNi

SiPt CrMn

Fe

Ni

200 300 400 500 600 700 800 900 10100Energy (keV)

00

04

09

13

18

22

KCnt

(d)

Figure 13 EDX spectroscopy analysis for worn surfaces at marked spots in Figure 12

12 Advances in Materials Science and Engineering

during PSR was always lower with no apparent fluctuationduring the steady-stage level due to the minimum tangentialforce between the contact interfaces where the central zoneswere mechanically interlocked In this case the highernormal load triggers the traction coefficient where thecritical total sliding shear force is always higher than thetangential force [5 11] However in GSR the highest peak offriction occurred prior to the fluctuating steady-stage levelmainly due to the strong plastic deformation of work-hardened layer of the contacting surfaces [23 29] On theother hand the fluctuations in COF are attributed to themodifications in the contact interface which are linked to thethird-body rheology ie wear debris formation and itsentrapment and ejection from the contact zone [27]

e fretting loops generated by Ft-D curves in Figure 9are good indicators to show the slip condition at any mo-ment e area enclosed by the curves is the measure ofdissipated energy produced by friction [10 30] e frictionwork performed provides a more representative explanationof the surface damage Usually it has been noticed that thewear volume V is proportional to the energy dissipated Edin the contact and described as V αtimes 1113936Ed where α is thefriction energy wear coefficient [6] e degree of slope Sccan be considered as wear characteristics of the slidingconditions and materials Besides the unified slip indexapproach also offers the knowledge of fretting conditionsand considered as an appropriate means for estimatingfretting wear problems In accordance with the terms of slipindex when the slip ratio s⟶ 0 the contacts are in stickand as the slip ratio approaches to 1 partial slip and thengross slip prevail [2] e partial slip contacts in smalldisplacements induce cyclic stresses which favor cracknucleation and propagation but the loading condition isnondissipative with limited surface damage at the peripheryas shown in Figure 10 However the friction dissipation inGSR correlated with the plastic flow delamination andoxidation wear mechanisms causes a large amount ofsurface damage by extending the contact area and reducingthe contact pressure profile (Figure 11)

e main damage mechanisms ie cracking (frettinginduced by fatigue) and material loss (fretting induced bywear) are often appear as a competing process which wasextensively explored during the last decade [1 3 5 6 31ndash34]For instance the material loss during GSR can eliminatesmall cracks or fill up the opening of a deep crack andaccommodate the main portion of the imposed displace-ment as a consequence it strongly reduces the slip am-plitude and then the debris formation In fact the debrisejection has great impact on the third-body establishment ifit is trapped between the contacts the degradation processcan be suppressed and the most of the velocity differencebetween the friction pairs would be completely accommo-dated in a dissipative manner by the powder bed [33 34] Asfor cracking the effects of frictional force and the contactload are huge on the crack initiation and growth duringfretting fatigue where the frictional force triggers the crackinitiation while the contact load disrupts the crack growthduring the propagation period [37] Meanwhile it is re-ported that the cracks on the worn scar surface nucleated

and propagated along the direction of 30ndash50deg to the surfaceinterior which was in the range of calculated maximumshear stress angle [18]

SEM morphology in Figure 12(a) shows the interestingwear phenomenon where the thick layer of Inconel X-750alloy was stuck to the worn surface of the oscillating ball dueto the adhesive microslip In return with the further frettingthe material transferred to the surface of GCr14 ball has thehighest possibility to transfer back to the previous wornsurface of Inconel X-750 alloy [8] Besides the transferredwear layer was highly oxidized compared to the stick and slipregions of the steel ball as shown in Figure 13 e debrisdetached from the contact pairs is essentially composed ofnonmagnetic single component oxides eg Fe2O3 NiO andCr2O3 or more complex oxides eg NiCr2O4 and NiFe2O4[38] However the oxidization process was rapid on theworn surface of the steel ball during GSR which is because ofmore mechanical energy being converted to the thermalheat and it is believed that the frictional heat during GSRwas higher than in PSR [19]

5 Conclusion

e main purpose of this study was to explore the degra-dation evolutions of Inconel X-750 co-acted with GCr15steel ball through the dry fretting tests and observationsanalyses by using 3D surface profiler SEM and EDXAccording to the results the conclusions can be drawn asfollows

(i) e degradation mechanisms of Inconel X-750 weretotally dependent on the fretting regimes and variedwith the fretting time

(ii) e wear volume and wear depth were very low inPSR and wear mechanisms were associated with thedeformations adhesion and fatigue crack emicrocracks were present around the stick domainin 3times104 cycle and the radial cracks fully coveredthe contact center above 105 cycle along with thebigger crack in the contact border e large layer ofductile X-750 alloy was transferred to the wearsurface of the steel ball due to the exhaustion byhighly concentrated cyclic loading during the laterstages of fretting

(iii) In GSR the degradation mechanisms were as fol-lows (1) adhesive wear (galling and scuffing) (2)abrasive wear by third-body particle which is amechanical removal process (3) delaminationwhich is influenced by the material fatigue in theshallow subsurface layer and (4) oxidation of debrisparticles and surface layer due to the higher fric-tional heat which can enhance the load-carryingcapacity as well as reduce the wear rate in the laterstages of fretting process

(iv) e dependence of fretting time was negligibleduring PSR in respect of wear properties such aswear volume scar area and depth However it has agreat impact to evolve the degradation mechanisms

Advances in Materials Science and Engineering 13

from asperity deformation to the crack initiationand propagation which is a critical damage duringPSR On the other hand the wear volume and scararea were increased significantly by time duringGSR but the degradation evolutions were combinedand repeated with the mentioned wear mechanismsin a whole fretting process

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

e first author would like to acknowledge the scholarshipsupport from China Scholarship Council (CSC) is workwas supported by the Aeronautical Science Fund of China(Grant no 20164058002) National Natural Science Foun-dation of China (Grant No51735006) and Tsinghua Uni-versity Initiative Scientific Research Program

References

[1] R B Waterhouse ldquoFretting wearrdquo Wear vol 100 no 1ndash3pp 107ndash118 1984

[2] M Varenberg I Etsion and G Halperin ldquoSlip index a newunified approach to frettingrdquo Tribology Letters vol 17 no 3pp 569ndash573 2004

[3] O Vingsbo and S Soderberg ldquoOn fretting mapsrdquo Wearvol 126 no 2 pp 131ndash147 1988

[4] R D Mindlin and H Deresiewiez ldquoElastic spheres in contactunder varying oblique forcesrdquo Journal of Applied Mechanicsvol 20 pp 327ndash344 1953

[5] Z R Zhou and L Vincent ldquoMixed fretting regimerdquo Wearvol 181ndash183 pp 531ndash536 1995

[6] S Fouvry P Kapsa and L Vincent ldquoQuantification offretting damagerdquo Wear vol 200 no 1-2 pp 186ndash205 1996

[7] J Yu L Qian B Yu and Z Zhou ldquoNanofretting behavior ofmonocrystalline silicon (100) against SiO2 microsphere invacuumrdquo Tribology Letters vol 34 no 1 pp 31ndash40 2009

[8] H Mohrbacher J P Celis and J R Roos ldquoLaboratory testingof displacement and load induced frettingrdquo Tribology In-ternational vol 28 no 5 pp 269ndash278 1995

[9] Z R Zhou S Fayeulle and L Vincent ldquoCracking behaviourof various aluminium alloys during fretting wearrdquo Wearvol 155 no 2 pp 317ndash330 1992

[10] S Fouvry P Kapsa H Zahouani and L Vincent ldquoWearanalysis in fretting of hard coatings through a dissipatedenergy conceptrdquo Wear vol 203-204 pp 393ndash403 1997

[11] J Li and Y H Lu ldquoEffects of displacement amplitude onfretting wear behaviors and mechanism of Inconel 600 alloyrdquoWear vol 304 no 1-2 pp 223ndash230 2013

[12] G B Stachowiak and G W Stachowiak ldquoFretting wear andfriction behaviour of engineering ceramicsrdquo Wear vol 190no 2 pp 212ndash218 1995

[13] B Bhushan and B K Gupta Handbook of Tribology Mate-rials Coatings and Surface Treatments McGraw-Hill NewYork NY USA 1991

[14] H Y Zhang Y H Lu M Ma and J Li ldquoEffect of precipitatedcarbides on the fretting wear behavior of Inconel 600 alloyrdquoWear vol 315 no 1-2 pp 58ndash67 2014

[15] X Mi W X Wang X M Xiong et al ldquoInvestigation offretting wear behavior of Inconel 690 alloy in tubeplatecontact configurationrdquoWear vol 328-329 pp 582ndash590 2015

[16] L Jie L Yonghao Z Haoyang and L Xin ldquoEffect of grain sizeand hardness on fretting wear behavior of inconel 600 alloysrdquoTribology International vol 81 pp 215ndash222 2015

[17] L Xin B B Yang Z H Wang J Li Y H Lu and T ShojildquoMicrostructural evolution of subsurface on inconel 690TTalloy subjected to fretting wear at elevated temperaturerdquoMaterials amp Design vol 104 pp 152ndash161 2016

[18] J Li B B Yang Y H Lu L Xin Z H Wang and T Shojildquoe degradation mechanism of inconel 690TT induced byfretting wear in airrdquo Tribology International vol 116pp 147ndash154 2017

[19] G Xianglong L Ping T Lichen et al ldquoEffects of slidingamplitude and normal load on the fretting wear behavior ofalloy 690 tube exposed to high temperature waterrdquo TribologyInternational vol 116 pp 155ndash163 2017

[20] Special Metals INCONEL alloy X-750 Data Sheet 2004Publication No SMC-067 httpwwwspecialmetalscom

[21] C Marsh S Depinoy and D Kaoumi ldquoEffect of heattreatment on the temperature dependence of the fracturebehavior of X-750 alloyrdquo Materials Science and EngineeringA vol 677 pp 474ndash484 2016

[22] D Wenbo S Yanhua D Chunhua and Y Lie ldquoStructuralstiffness of X-750 alloy bump foil strips for compliant foilbearings with different heat treatmentsrdquo Journal of Tribologyvol 138 no 3 article 031702 2016

[23] G X Chen and Z R Zhou ldquoStudy on transition betweenfretting and reciprocating sliding wearrdquo Wear vol 250no 1ndash12 pp 665ndash672 2001

[24] J F Archard ldquoContact and rubbing of flat surfacesrdquo Journal ofApplied Physics vol 24 no 8 pp 981ndash988 1953

[25] S C Lim M F Ashby and J H Brunton ldquoWear-ratetransitions and their relationship to wear mechanismsrdquoActa Metallurgica vol 35 no 6 pp 1343ndash1348 1987

[26] S C Lim ldquoRecent developments in wear-mechanism mapsrdquoTribology International vol 31 no 1ndash3 pp 87ndash97 1998

[27] X LongW Zihao L Jie Y Lu and T Shoji ldquoMicrostructuralcharacterization of subsurface caused by fretting wear ofinconel 690TT alloyrdquo Material Characteristics vol 115pp 32ndash38 2016

[28] R Rybiak S Fouvry and B Bonnet ldquoFretting wear of stainlesssteels under variable temperature conditions introduction ofa ldquocompositerdquo wear lawrdquoWear vol 268 no 3-4 pp 413ndash4232010

[29] J F Zheng J Luo J L Mo J F Peng X S Jin andMH ZhuldquoFretting wear behaviors of a railway axle steelrdquo TribologyInternational vol 43 no 5-6 pp 906ndash911 2010

[30] K V Virendra N Hamza S S R Ganesh H MurthyA N Majila and D C Fernando ldquoEffect of contact pressureand stress ratio on the fretting fatigue behaviour of Ti-6Al-4Vrdquo Material Science and Engineering A vol 707 pp 647ndash656 2017

[31] J J Madge S B Leen and P H Shipway ldquoe critical role offretting wear in the analysis of fretting fatiguerdquoWear vol 263no 1ndash6 pp 542ndash551 2007

14 Advances in Materials Science and Engineering

quantities also can be displayed as a force-displacement (Ft-D) hysteresis loop or fretting loop which is recorded byfriction signal analysis module (FSA) for every frettingcycles Moreover slip regimes were also conrmed by theuniversal slip index δ criterion which was mentioned above

After the samples were collected from fretting tests theywere ultrasonically cleaned again with acetone to removeloose debris from wear scar and postexperimental analyseswere carried out to investigate wear volumes and surfacemorphologies Surface topography information was ob-tained by employing the noncontact 3D optical proler(Zygo Nexview AMETEK Inc USA) to measure the wearvolume under the at surface prole and to generate in-teractive 3D plots as well as cross-section proles of thewear scar In order to have a high-quality morphologyanalysis the worn surfaces were coated with platinum (Pt) in842 nm thickness with 011 nms sputter rate for 75 secondsScanning electron microscopy (SEM) investigations wereconducted by TESCAN LYRA3 (Czech Republic) in

23eminus 2 Pa vacuum chamber pressure and electron beamwith 20 kV to reveal the degradation mechanisms on theworn surface during dierent fretting regimes Oxide con-tents and other chemical compositions on the worn surfaceswere detected by using the energy-dispersive X-ray spec-troscopy (EDX) embedded analyzer

Table 1 Chemical compositions for the frictional pairs (wt)

MaterialsElements

Ni Cr Fe Ti Al Nb+Ta Mn Si S Cu C CoInconel X-750 716 145 58 26 05 083 062 02 001 001 003 001GCr15 03 146 Bal mdash mdash mdash 036 019 0025 006 096 mdash

No damage Crack WearStick PSR GSR

Reci

proc

al sl

idin

g

Nor

mal

forc

e

Displacement amplitude

(a)

2As

2Ad

Slip ratio s = AsAd

Slip index δ = AdScP

Ft

D s = 1 ndash 12δ

Partial slip 05 le δ lt 06Gross slip 08 lt δ lt 10

Reciprocal sliding δ gt 11

Ed

Sc

(b)

Figure 1 Fretting map for fretting regimes and material response (a) and fretting loop by tangential force vs displacement amplitude (b)(reproduced from Reference [2])

Loading system

Oscillating rod

X-750 alloydisk

GCr15steel ball

Oscillating rod

Piezotransducer Heating cartridge

1cm

Figure 2 SRV 4 fretting wear test device

Table 2 Fretting test parameters

Parameters ValuesNormal load 100NDisplacement amplitude 40 microm 100 micromFrequency 50Hz 20Hz

Number of cycles30000 1200090000 36000270000 108000

Linear speed 8mmsTotal distance 48m 144m 432mRelative humidity 50ndash60

Advances in Materials Science and Engineering 3

3 Results

31 Wear Characteristics e SEM images of wear scars onthe lower specimens and superimposed cross-section pro-files perpendicular to the fretting direction are shown inFigures 3 and 4 for different amplitudes through the frettingtime respectively As can be seen the worn surfaces were ina circular shape for both displacement amplitudes but with aslight elongation in the direction of fretting for the initialstages of 100 microm amplitude e fretted surfaces were roughall over and as the displacement amplitude increases thesize of the worn surface was significantly increased over time(width from 1250 microm to 1750 microm) which indicates fullsliding in the whole contact area In contrast in the case of40 microm the shape of the wear scars was remaining almostsame for all fretting tests and very similar to Mindlinrsquosdefinition in which the central stick region was formedbecause of higher contact stresses in the center while theslight slip was observed in the periphery of the contact due tostick-slip effect [4]

e stick region which was 150 microm in radius (smallerthan Hertzian contact radius of 296 microm) after 10minutes offretting became narrower twice as much after 90minutes offretting test covered with cracks by the effect of repetitivecyclic stresses

It is obvious in Figure 4 that the wear scars for 100 micromwere wider and deeper than 40 microm In the initial phases offretting the cross-section profiles in PSR demonstratedconcave pit due to higher contact pressure while a bulk ofmaterials was transferred to the contact borders in GSR dueto plastic deformation Later in Figure 4(c) the wear scarsevolved to ldquoWrdquo shape cross section after 90minutes offretting for both PSR and GSR For gross slip conditions thiscan be explained with the load-carrying wear debris layerwhich was mostly generated in the contact annulus ratherthan in contact center thus bearing contact pressures near tothe contact border [10] On the other hand some asperitieswere popped up at the contact center in PSR while theperipheral contact region was smooth due to the microslipoccurrence It was evaluated through fretting experimentsthat the wider asperity areas were observed in the contactcenter with the smaller imposed displacement amplitudesand the greater normal loads [23]

3D surface mapping and noncontacting wear volumeand worn area measurements were obtained by 3D opticalsurface profiler as illustrated in Figure 5 is process takesthe initial step of capturing the millions of data points in thewear scar region with high-precision objective lenses fol-lowed by the selection of worn area to calculate the wearvolume under the original flat surface as depicted inFigures 5(b) and 5(c) Figure 6 gives the information ofcalculated wear volume worn area and wear rate as afunction of time for both imposed displacement amplitudesWear volumes and worn surface areas have grown dra-matically at 100 microm displacement amplitude (ie 37times

106 microm3 and 94times104 microm2 after 10min and 134times106 microm3

and 226times104 microm2 after 90min respectively) while theprogress of wear volume and scar area was very small at40 microm displacement amplitude almost negligible values of

065 to 084times106 microm3 and 3 to 34times104 microm2 after 10min and90min respectively

e wear rate which is defined to be the volume ofmaterial removed per unit sliding distance WVs wasdecreasing gradually during fretting process for both im-posed displacement amplitudes as shown in Figure 6(c)is process is usually attributed to the running-in orbreaking-in effects in the initial fretting periods where theinitial wear rate is higher and slowly lowers while thecontacting surfaces evolve to their steady-state of wear [24]Besides for steel sliding in air the rise in temperature fromfrictional heating promotes surface oxidation Conse-quently the wear rate decreases due to the oxide film for-mation which provides a protective layer against furtherwear [25 26]

32 Coefficient of Friction Friction between two countersurfaces was due to the various combined effects of adhesionand abrasion by wear particles and hard asperities de-formations e degree of friction is expressed as a co-efficient of friction (micro) which is the ratio of tangential force(Ft) to the normal load (P) and shown in Figure 7 as afunction of time For both imposed displacement ampli-tudes rapid growth in COF was observed in the beginning offretting test in a few seconds almost jumping to 08 value At40 microm displacement amplitude the contact is subjected topartial slip with junction of adhesion and sliding zones thusthe tangential force remains less than the product of appliednormal load and the static friction coefficient is tendencyis described by Ftlt microP and COF continued in a steady pacefor the rest of the test But at 100 microm coefficient of frictionwas decreasing suddenly dropping to 07 for a few tenseconds followed by gradual increase to the value of 09 afterabout 400 s and kept at steady-state level As far as largerrelative motion is concerned this initial rapid rise in COF isbelieved to be due to the rupture of the ldquowork-hardeningrdquo orcontaminant layer of the surface [16 18] e highest wearrate would also be possibly associated with the mass elim-ination of the contact surface in this period of fretting

In this experiment the friction signal was sinusoidalduring the entire test without break as portrayed in Figure 8e variation of coefficient of friction is plotted during the600th second for both imposed amplitudes In Figure 8(a) apure periodic sine wave was observed in the case of PSRwhen the amplitude was 40 microm because the frictional forcein the contact interface as a reaction to the imposed am-plitude was not enough to cause a full slide In Figure 8(b)the curve of coefficient of friction at 100 microm was formed as asine wave with clipped peaks which indicates the full slidebetween frictional pairs

33 Fretting Loop In most of the theoretical and experi-mental works the decisions of fretting regime and degra-dation mechanisms are made based on the ldquofretting looprdquowhich is defined by ldquoforce-displacementrdquo curve [3 5 6 9ndash12]Figure 9 shows the comparative Ft-D curves for partial andgross slip at the onset (after 5min) and the end (after 90min)of the fretting test e partially closed and elliptical curve

4 Advances in Materials Science and Engineering

which corresponds to PSR was obtained for 40 microm inFigure 9(a) However due to the continuation of cyclic loadsthe central mechanical interlocking was reduced and theclosed part of the loop was slightly widened after 90minis situation is related to the transition from primary elasticto plastic shear form and also due to the limited relative slipand small surface modification at higher normal loadParallelogram Ft-D curves at 100 microm attributed to GSRwhere displacement amplitude and thus the area of dissi-pated energy in the contact interface were greater In thiscase full sliding prevailed in the whole contact interfaceresulting in a higher rate of particle detachment and relativemotions were predominantly accommodated by plasticdeformation of counter surfaces during the entire fretting

processe fretting loop was kept almost unchanged for therest of the tests Besides fretting regimes according to theslip index criterion were also confirmed which can be cal-culated as shown in Figure 1(b) and δ found to be 056 forPSR while δ 106 for GSR both cases satisfying thetransition restrictions for slip index

34 Worn Scar Morphology e consequences of thesementioned frictional effects on the Inconel X-750 alloy andGCr15 steel ball specimens were investigated for partial andgross slip conditions by observing SEM morphologiesFigure 10 shows the damage evolutions on the flat material atthe stick and slip domains when the displacement amplitude

D = 40microm D = 100microm

(a)

D = 40microm D = 100microm

(b)

D = 40microm D = 100microm

(c)

Figure 3 SEM images of worn scars on Inconel X-750 alloy after (a) 10 (b) 30 and (c) 90minutes of fretting tests Double arrow indicatesfretting direction

Advances in Materials Science and Engineering 5

at 40 microm It was found that PSR was dominant in the contactarea with the mechanical interlocking of the asperities in thecontact center and adhered fretting scars due to themicroslips in the contact annulus However the degree ofthese degradation mechanisms was changing over thenumber of fretting cycles For instance Figure 10(a) showsthe fretting scars after 10min with limited material damagethe stick domain was smooth and surrounded by tiny pitsdue to the ratcheting eect In the later stages of frettingcycles (9times104) manymicrocracks surrounded the shrinkingstick area while the long crack perpendicular to the frettingdirection appeared in the contact border which looks like inthe stage of delamination process (Figure 10(b)) Further-more the sign of thick layer of material removal by harderGCr15 ball was observed in the slip region copye contactcenter was slowly worn out during the further fretting test by

overstressing and the wear mode was completely changedafter a considerable number of cycles (27times105) as shown inFigure 10(c) where the stick domain was totally rough andcovered with radial microcracks which were induced byfretting fatigue On the other hand the longer crack wasdetected along the far end of the contact which was partiallylled with wear debriscopye slip region also has been changedsince the previous condition where some layer of the an-nulus was transferred by opposite surface and this time theremaining layers of the contact annulus was removed byfurther cyclic stress which was assumed to be the exhaustionof ductility due to the plasticity accumulation by ratcheting

SEM morphologies in Figure 11 shows that the wholecontact interface was in full slide at 100 microm and degradationmechanisms were associated with adhesion abrasion de-lamination oxidation and plastic deformation as well as

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

μm

μm

0

5

10

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

(a)

μm

μm

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

ndash25

ndash30

ndash20

ndash15

ndash10

ndash5

0

5

10

(b)

μm

μm

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

5

10

(c)

Figure 4 Superimposed cross-section proles of wear scars perpendicular to the fretting direction through fretting time (a) After10minutes (b) After 30minutes (c) After 90minutes

6 Advances in Materials Science and Engineering

third-body flow between contact surfaces Red-brown oxi-dized powders were ejected from contact surfaces during thefretting process which can serve as abrasive particles prior totheir expulsion For example Figure 11(a) shows the wearmode onset of the fretting process in the contact centerwhere plowing grooves parallel to the sliding direction was

formed due to the larger relative motion by abrasive par-ticles followed by plastic shearing so that thick layers ofX-750 alloy were peeled off by adhesion Adhesive wear isoften occurred at the onset of fretting when friction pairscome into contact followed by plastic shearing that plucksoff the ends of the softer asperities is phenomenon is also

(a)

(b)

(c)

Figure 5 Surface topographies of worn scars for (a) 40 microm (left) and 100 microm (right) after 90minutes of fretting test (b) correspondingpreprocessed input area and (c) selected worn area to calculate the wear volume

Advances in Materials Science and Engineering 7

150

125

100W

ear v

olum

e los

s (lowast

106 micro

m3 )

75

50

25

0040

Displacement amplitude (microm)100

Aer 10 minutesAer 30 minutesAer 90 minutes

(a)

24

21

18

15

12

9

6

3

0

Wor

n sc

ar ar

ea (lowast

104 micro

m2 )

Displacement amplitude (microm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(b)

900

750

600

450

300

150

0

Wea

r rat

e (μm

3 mm

)

Displacement amplitude (μm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(c)

Figure 6 Calculated wear volumes (a) worn scar areas (b) and wear rates (c) after dierent time of fretting

00

02

04

06

08

10

12

0 600 1200 1800 2400 3000Time (s)

Coeffi

cien

t of f

rictio

n

3600 4200 4800 5400

40 microm100 microm

Figure 7 Coeordfcient of friction for contact pairs as a function of time

8 Advances in Materials Science and Engineering

attributed to galling and scuordfng [13] Figure 11(b) shows themagnied image in Figure 11(a) that the crack propagationswere prevented by particle detachment and started to spall

eventually becoming loose wear debris Fretted surfaces wererough owing to the plastic deformation and ploughing ef-fects and in some cases surface roughening would provide

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(a)

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(b)

Figure 9 Evolution of fretting loops for 40 microm and 100 microm after (a) 5 and (b) 90minutes of fretting

125100075050025000

ndash025ndash050ndash075ndash100ndash125

60001 60002 60003Time (s)

Coef

ficie

nt o

f fric

tion

60004 60005

40microm

(a)

Time (s)

125100075050025000

ndash025ndash050ndash075ndash100ndash125

Coef

ficie

nt o

f fric

tion

100microm

60001 60002 60003 60004 60005

(b)

Figure 8 Sinusoidal coeordfcient of frictions during 600 s fretting time for (a) 40 microm and (b) 100 microm

Advances in Materials Science and Engineering 9

escape channels for wear debris As the fretting test con-tinued the contact interfaces were slowly accommodated bythe plastic flow and further loading promoted the growth ofsubsurface cracks that parallel to the surface When thesecracks finally extended out to the free surface thin platelet-like wear particles delaminated as shown in Figures 11(c)and 11(d) In the same time when the delamination wasoccurring mostly in the contact center plastic flow of thecontacting surfaces in the periphery and third-body flowclose to the contact border were observed in Figures 11(e)and 11(f) respectively Moreover as temperature increasesbecause of frictional heating during GSR oxidation of thewear particles becomes more ubiquitous and as a

consequence thicker more continuous oxide layer will begenerated e greater contact temperature at this conditionalso causes plastic flow of the oxide film leading to moresevere oxidational wear [19]

Figure 12 shows the SEM images of wear scars andcorresponding 3D surface topographies of the steel ballsoscillated at 40 microm and 100 microm after 90minutes of frettingBoth wear scars were in a circular shape e worn surfacearea which was oscillated at 40 microm also contains the stickdomain in the contact center and slip domain at the pe-riphery as shown in Figure 12(a) However it is clear fromthe picture that a bulk of oxidized X-750 alloy surface layerin black was adhered to the half annulus of the contact which

Slip region

Stick region

Micropitboundary

Slip region

Adhesive microslip

(a)

Stick region

Microcracks

Slip region

Adhesive layerremoval

Crack delamination

(b)

Stick region

Cracks

Slip region

New crack growth alongthe contact border

(c)

Figure 10 SEMmicrographs of Inconel X-750 wear scars during PSR (a) after 10minutes (b) after 30minutes and (c) after 90minutes offretting Displacement amplitude is 40 microm Double arrows represent fretting direction

10 Advances in Materials Science and Engineering

was believed to be plucked off by harder GCr15 ball surfaceduring fretting induced by fatigue According to the wearscar in Figure 12(b) GSR was dominant at 100 microm with thesign of abrasion and small amount of transferred materialson the worn surface Figure 13 shows the EDX spectruminformation for the marked spots in Figure 12 on the wearscar areas Oxide content was very low (146 wt) in thestick region due to the constriction of the relative motionwhile microslip region was reacting with the oxygen in asmall amount On the other hand the highly concentratedoxygen content (29 wt) was detected on the transferredflat material in Figure 13(c) However the oxidation process

on the worn steel surface was faster during GSR rather thanPSR (Figure 13(d))

4 Discussion

e fretting wear process in an ambient temperature is oftendetermined by the contact geometry the oxidation processand the subsequent third-body behavior in the contact in-terface which significantly affect the friction and wearproperties in dry air [11 16 27] Wear properties such asvolume scar area and depth were considerably lowerduring PSR than GSR as shown in Figures 3ndash6 because of

(b)

Adhesive shear

Plowing

(a)

Crack spalling

(b)

Delamination

(c)

Delamination

Oxide layers

(d)

Plastic flow

(e)

Oxidized third-body flow

(f )

Figure 11 SEMmicrographs of Inconel X-750 wear scars during GSR (a) mixed abrasive and adhesive wear at the onset of fretting process(b) spalling of cracks (c d) delamination (e) plastic flow and (f) third-body flow near contact border Displacement amplitude is 100 micromDouble arrows represent fretting direction

Advances in Materials Science and Engineering 11

the small imposed contact area compared to the scale of thenormal load applied Yet the wear rate was maximum in therunning-in period for both cases decreasing gradually withfretting time in Figure 6(c) typically due to the formation ofthe oxide layer (also ldquoglazerdquo layer) on the worn surface which

can enhance the load-carrying capacity avoiding furtherwear [28] During the partial and gross slip conditions thefriction is the outcome of the direct interlocking of thesurface asperities and the trapped oxide debris behavior inthe contact interface respectively In Figure 7 the COF

Highly oxidized Inconel X-750alloy wear layer transfer

a b c

(a)

d

Oxidization

(b)

Figure 12 SEM morphologies of GCr15 steel ball worn scars oscillating at (a) 40 microm and (b) 100 microm Fretting time is 90minutes Doublearrows represent fretting direction

C

O

Fe

Ni SiPt CrMn

Fe

Ni

O KCr KFe KNi K

Element0653wt

019687490056

1888at

017572460044

00

06

12

17

23

29

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(a)

CO

Fe

NiSiPt Cr Mn

Fe

Ni

O KCr KFe KNi K

Element0146wt

026391270104

0470at

026184190091

200 300 400 500 600 700 800 900 10100Energy (keV)

00

05

10

16

21

26

KCnt

(b)

O KCr KFe KNi K

Element2959wt

107305115105

5793at

064702732863

C

O

FeNi SiPt

Cr

Mn Fe

Ni

00

06

12

18

24

30

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(c)

O KCr KFe KNi K

Element1499wt

020378570071

3572at

014953640046

C

O

FeNi

SiPt CrMn

Fe

Ni

200 300 400 500 600 700 800 900 10100Energy (keV)

00

04

09

13

18

22

KCnt

(d)

Figure 13 EDX spectroscopy analysis for worn surfaces at marked spots in Figure 12

12 Advances in Materials Science and Engineering

during PSR was always lower with no apparent fluctuationduring the steady-stage level due to the minimum tangentialforce between the contact interfaces where the central zoneswere mechanically interlocked In this case the highernormal load triggers the traction coefficient where thecritical total sliding shear force is always higher than thetangential force [5 11] However in GSR the highest peak offriction occurred prior to the fluctuating steady-stage levelmainly due to the strong plastic deformation of work-hardened layer of the contacting surfaces [23 29] On theother hand the fluctuations in COF are attributed to themodifications in the contact interface which are linked to thethird-body rheology ie wear debris formation and itsentrapment and ejection from the contact zone [27]

e fretting loops generated by Ft-D curves in Figure 9are good indicators to show the slip condition at any mo-ment e area enclosed by the curves is the measure ofdissipated energy produced by friction [10 30] e frictionwork performed provides a more representative explanationof the surface damage Usually it has been noticed that thewear volume V is proportional to the energy dissipated Edin the contact and described as V αtimes 1113936Ed where α is thefriction energy wear coefficient [6] e degree of slope Sccan be considered as wear characteristics of the slidingconditions and materials Besides the unified slip indexapproach also offers the knowledge of fretting conditionsand considered as an appropriate means for estimatingfretting wear problems In accordance with the terms of slipindex when the slip ratio s⟶ 0 the contacts are in stickand as the slip ratio approaches to 1 partial slip and thengross slip prevail [2] e partial slip contacts in smalldisplacements induce cyclic stresses which favor cracknucleation and propagation but the loading condition isnondissipative with limited surface damage at the peripheryas shown in Figure 10 However the friction dissipation inGSR correlated with the plastic flow delamination andoxidation wear mechanisms causes a large amount ofsurface damage by extending the contact area and reducingthe contact pressure profile (Figure 11)

e main damage mechanisms ie cracking (frettinginduced by fatigue) and material loss (fretting induced bywear) are often appear as a competing process which wasextensively explored during the last decade [1 3 5 6 31ndash34]For instance the material loss during GSR can eliminatesmall cracks or fill up the opening of a deep crack andaccommodate the main portion of the imposed displace-ment as a consequence it strongly reduces the slip am-plitude and then the debris formation In fact the debrisejection has great impact on the third-body establishment ifit is trapped between the contacts the degradation processcan be suppressed and the most of the velocity differencebetween the friction pairs would be completely accommo-dated in a dissipative manner by the powder bed [33 34] Asfor cracking the effects of frictional force and the contactload are huge on the crack initiation and growth duringfretting fatigue where the frictional force triggers the crackinitiation while the contact load disrupts the crack growthduring the propagation period [37] Meanwhile it is re-ported that the cracks on the worn scar surface nucleated

and propagated along the direction of 30ndash50deg to the surfaceinterior which was in the range of calculated maximumshear stress angle [18]

SEM morphology in Figure 12(a) shows the interestingwear phenomenon where the thick layer of Inconel X-750alloy was stuck to the worn surface of the oscillating ball dueto the adhesive microslip In return with the further frettingthe material transferred to the surface of GCr14 ball has thehighest possibility to transfer back to the previous wornsurface of Inconel X-750 alloy [8] Besides the transferredwear layer was highly oxidized compared to the stick and slipregions of the steel ball as shown in Figure 13 e debrisdetached from the contact pairs is essentially composed ofnonmagnetic single component oxides eg Fe2O3 NiO andCr2O3 or more complex oxides eg NiCr2O4 and NiFe2O4[38] However the oxidization process was rapid on theworn surface of the steel ball during GSR which is because ofmore mechanical energy being converted to the thermalheat and it is believed that the frictional heat during GSRwas higher than in PSR [19]

5 Conclusion

e main purpose of this study was to explore the degra-dation evolutions of Inconel X-750 co-acted with GCr15steel ball through the dry fretting tests and observationsanalyses by using 3D surface profiler SEM and EDXAccording to the results the conclusions can be drawn asfollows

(i) e degradation mechanisms of Inconel X-750 weretotally dependent on the fretting regimes and variedwith the fretting time

(ii) e wear volume and wear depth were very low inPSR and wear mechanisms were associated with thedeformations adhesion and fatigue crack emicrocracks were present around the stick domainin 3times104 cycle and the radial cracks fully coveredthe contact center above 105 cycle along with thebigger crack in the contact border e large layer ofductile X-750 alloy was transferred to the wearsurface of the steel ball due to the exhaustion byhighly concentrated cyclic loading during the laterstages of fretting

(iii) In GSR the degradation mechanisms were as fol-lows (1) adhesive wear (galling and scuffing) (2)abrasive wear by third-body particle which is amechanical removal process (3) delaminationwhich is influenced by the material fatigue in theshallow subsurface layer and (4) oxidation of debrisparticles and surface layer due to the higher fric-tional heat which can enhance the load-carryingcapacity as well as reduce the wear rate in the laterstages of fretting process

(iv) e dependence of fretting time was negligibleduring PSR in respect of wear properties such aswear volume scar area and depth However it has agreat impact to evolve the degradation mechanisms

Advances in Materials Science and Engineering 13

from asperity deformation to the crack initiationand propagation which is a critical damage duringPSR On the other hand the wear volume and scararea were increased significantly by time duringGSR but the degradation evolutions were combinedand repeated with the mentioned wear mechanismsin a whole fretting process

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

e first author would like to acknowledge the scholarshipsupport from China Scholarship Council (CSC) is workwas supported by the Aeronautical Science Fund of China(Grant no 20164058002) National Natural Science Foun-dation of China (Grant No51735006) and Tsinghua Uni-versity Initiative Scientific Research Program

References

[1] R B Waterhouse ldquoFretting wearrdquo Wear vol 100 no 1ndash3pp 107ndash118 1984

[2] M Varenberg I Etsion and G Halperin ldquoSlip index a newunified approach to frettingrdquo Tribology Letters vol 17 no 3pp 569ndash573 2004

[3] O Vingsbo and S Soderberg ldquoOn fretting mapsrdquo Wearvol 126 no 2 pp 131ndash147 1988

[4] R D Mindlin and H Deresiewiez ldquoElastic spheres in contactunder varying oblique forcesrdquo Journal of Applied Mechanicsvol 20 pp 327ndash344 1953

[5] Z R Zhou and L Vincent ldquoMixed fretting regimerdquo Wearvol 181ndash183 pp 531ndash536 1995

[6] S Fouvry P Kapsa and L Vincent ldquoQuantification offretting damagerdquo Wear vol 200 no 1-2 pp 186ndash205 1996

[7] J Yu L Qian B Yu and Z Zhou ldquoNanofretting behavior ofmonocrystalline silicon (100) against SiO2 microsphere invacuumrdquo Tribology Letters vol 34 no 1 pp 31ndash40 2009

[8] H Mohrbacher J P Celis and J R Roos ldquoLaboratory testingof displacement and load induced frettingrdquo Tribology In-ternational vol 28 no 5 pp 269ndash278 1995

[9] Z R Zhou S Fayeulle and L Vincent ldquoCracking behaviourof various aluminium alloys during fretting wearrdquo Wearvol 155 no 2 pp 317ndash330 1992

[10] S Fouvry P Kapsa H Zahouani and L Vincent ldquoWearanalysis in fretting of hard coatings through a dissipatedenergy conceptrdquo Wear vol 203-204 pp 393ndash403 1997

[11] J Li and Y H Lu ldquoEffects of displacement amplitude onfretting wear behaviors and mechanism of Inconel 600 alloyrdquoWear vol 304 no 1-2 pp 223ndash230 2013

[12] G B Stachowiak and G W Stachowiak ldquoFretting wear andfriction behaviour of engineering ceramicsrdquo Wear vol 190no 2 pp 212ndash218 1995

[13] B Bhushan and B K Gupta Handbook of Tribology Mate-rials Coatings and Surface Treatments McGraw-Hill NewYork NY USA 1991

[14] H Y Zhang Y H Lu M Ma and J Li ldquoEffect of precipitatedcarbides on the fretting wear behavior of Inconel 600 alloyrdquoWear vol 315 no 1-2 pp 58ndash67 2014

[15] X Mi W X Wang X M Xiong et al ldquoInvestigation offretting wear behavior of Inconel 690 alloy in tubeplatecontact configurationrdquoWear vol 328-329 pp 582ndash590 2015

[16] L Jie L Yonghao Z Haoyang and L Xin ldquoEffect of grain sizeand hardness on fretting wear behavior of inconel 600 alloysrdquoTribology International vol 81 pp 215ndash222 2015

[17] L Xin B B Yang Z H Wang J Li Y H Lu and T ShojildquoMicrostructural evolution of subsurface on inconel 690TTalloy subjected to fretting wear at elevated temperaturerdquoMaterials amp Design vol 104 pp 152ndash161 2016

[18] J Li B B Yang Y H Lu L Xin Z H Wang and T Shojildquoe degradation mechanism of inconel 690TT induced byfretting wear in airrdquo Tribology International vol 116pp 147ndash154 2017

[19] G Xianglong L Ping T Lichen et al ldquoEffects of slidingamplitude and normal load on the fretting wear behavior ofalloy 690 tube exposed to high temperature waterrdquo TribologyInternational vol 116 pp 155ndash163 2017

[20] Special Metals INCONEL alloy X-750 Data Sheet 2004Publication No SMC-067 httpwwwspecialmetalscom

[21] C Marsh S Depinoy and D Kaoumi ldquoEffect of heattreatment on the temperature dependence of the fracturebehavior of X-750 alloyrdquo Materials Science and EngineeringA vol 677 pp 474ndash484 2016

[22] D Wenbo S Yanhua D Chunhua and Y Lie ldquoStructuralstiffness of X-750 alloy bump foil strips for compliant foilbearings with different heat treatmentsrdquo Journal of Tribologyvol 138 no 3 article 031702 2016

[23] G X Chen and Z R Zhou ldquoStudy on transition betweenfretting and reciprocating sliding wearrdquo Wear vol 250no 1ndash12 pp 665ndash672 2001

[24] J F Archard ldquoContact and rubbing of flat surfacesrdquo Journal ofApplied Physics vol 24 no 8 pp 981ndash988 1953

[25] S C Lim M F Ashby and J H Brunton ldquoWear-ratetransitions and their relationship to wear mechanismsrdquoActa Metallurgica vol 35 no 6 pp 1343ndash1348 1987

[26] S C Lim ldquoRecent developments in wear-mechanism mapsrdquoTribology International vol 31 no 1ndash3 pp 87ndash97 1998

[27] X LongW Zihao L Jie Y Lu and T Shoji ldquoMicrostructuralcharacterization of subsurface caused by fretting wear ofinconel 690TT alloyrdquo Material Characteristics vol 115pp 32ndash38 2016

[28] R Rybiak S Fouvry and B Bonnet ldquoFretting wear of stainlesssteels under variable temperature conditions introduction ofa ldquocompositerdquo wear lawrdquoWear vol 268 no 3-4 pp 413ndash4232010

[29] J F Zheng J Luo J L Mo J F Peng X S Jin andMH ZhuldquoFretting wear behaviors of a railway axle steelrdquo TribologyInternational vol 43 no 5-6 pp 906ndash911 2010

[30] K V Virendra N Hamza S S R Ganesh H MurthyA N Majila and D C Fernando ldquoEffect of contact pressureand stress ratio on the fretting fatigue behaviour of Ti-6Al-4Vrdquo Material Science and Engineering A vol 707 pp 647ndash656 2017

[31] J J Madge S B Leen and P H Shipway ldquoe critical role offretting wear in the analysis of fretting fatiguerdquoWear vol 263no 1ndash6 pp 542ndash551 2007

14 Advances in Materials Science and Engineering

3 Results

31 Wear Characteristics e SEM images of wear scars onthe lower specimens and superimposed cross-section pro-files perpendicular to the fretting direction are shown inFigures 3 and 4 for different amplitudes through the frettingtime respectively As can be seen the worn surfaces were ina circular shape for both displacement amplitudes but with aslight elongation in the direction of fretting for the initialstages of 100 microm amplitude e fretted surfaces were roughall over and as the displacement amplitude increases thesize of the worn surface was significantly increased over time(width from 1250 microm to 1750 microm) which indicates fullsliding in the whole contact area In contrast in the case of40 microm the shape of the wear scars was remaining almostsame for all fretting tests and very similar to Mindlinrsquosdefinition in which the central stick region was formedbecause of higher contact stresses in the center while theslight slip was observed in the periphery of the contact due tostick-slip effect [4]

e stick region which was 150 microm in radius (smallerthan Hertzian contact radius of 296 microm) after 10minutes offretting became narrower twice as much after 90minutes offretting test covered with cracks by the effect of repetitivecyclic stresses

It is obvious in Figure 4 that the wear scars for 100 micromwere wider and deeper than 40 microm In the initial phases offretting the cross-section profiles in PSR demonstratedconcave pit due to higher contact pressure while a bulk ofmaterials was transferred to the contact borders in GSR dueto plastic deformation Later in Figure 4(c) the wear scarsevolved to ldquoWrdquo shape cross section after 90minutes offretting for both PSR and GSR For gross slip conditions thiscan be explained with the load-carrying wear debris layerwhich was mostly generated in the contact annulus ratherthan in contact center thus bearing contact pressures near tothe contact border [10] On the other hand some asperitieswere popped up at the contact center in PSR while theperipheral contact region was smooth due to the microslipoccurrence It was evaluated through fretting experimentsthat the wider asperity areas were observed in the contactcenter with the smaller imposed displacement amplitudesand the greater normal loads [23]

3D surface mapping and noncontacting wear volumeand worn area measurements were obtained by 3D opticalsurface profiler as illustrated in Figure 5 is process takesthe initial step of capturing the millions of data points in thewear scar region with high-precision objective lenses fol-lowed by the selection of worn area to calculate the wearvolume under the original flat surface as depicted inFigures 5(b) and 5(c) Figure 6 gives the information ofcalculated wear volume worn area and wear rate as afunction of time for both imposed displacement amplitudesWear volumes and worn surface areas have grown dra-matically at 100 microm displacement amplitude (ie 37times

106 microm3 and 94times104 microm2 after 10min and 134times106 microm3

and 226times104 microm2 after 90min respectively) while theprogress of wear volume and scar area was very small at40 microm displacement amplitude almost negligible values of

065 to 084times106 microm3 and 3 to 34times104 microm2 after 10min and90min respectively

e wear rate which is defined to be the volume ofmaterial removed per unit sliding distance WVs wasdecreasing gradually during fretting process for both im-posed displacement amplitudes as shown in Figure 6(c)is process is usually attributed to the running-in orbreaking-in effects in the initial fretting periods where theinitial wear rate is higher and slowly lowers while thecontacting surfaces evolve to their steady-state of wear [24]Besides for steel sliding in air the rise in temperature fromfrictional heating promotes surface oxidation Conse-quently the wear rate decreases due to the oxide film for-mation which provides a protective layer against furtherwear [25 26]

32 Coefficient of Friction Friction between two countersurfaces was due to the various combined effects of adhesionand abrasion by wear particles and hard asperities de-formations e degree of friction is expressed as a co-efficient of friction (micro) which is the ratio of tangential force(Ft) to the normal load (P) and shown in Figure 7 as afunction of time For both imposed displacement ampli-tudes rapid growth in COF was observed in the beginning offretting test in a few seconds almost jumping to 08 value At40 microm displacement amplitude the contact is subjected topartial slip with junction of adhesion and sliding zones thusthe tangential force remains less than the product of appliednormal load and the static friction coefficient is tendencyis described by Ftlt microP and COF continued in a steady pacefor the rest of the test But at 100 microm coefficient of frictionwas decreasing suddenly dropping to 07 for a few tenseconds followed by gradual increase to the value of 09 afterabout 400 s and kept at steady-state level As far as largerrelative motion is concerned this initial rapid rise in COF isbelieved to be due to the rupture of the ldquowork-hardeningrdquo orcontaminant layer of the surface [16 18] e highest wearrate would also be possibly associated with the mass elim-ination of the contact surface in this period of fretting

In this experiment the friction signal was sinusoidalduring the entire test without break as portrayed in Figure 8e variation of coefficient of friction is plotted during the600th second for both imposed amplitudes In Figure 8(a) apure periodic sine wave was observed in the case of PSRwhen the amplitude was 40 microm because the frictional forcein the contact interface as a reaction to the imposed am-plitude was not enough to cause a full slide In Figure 8(b)the curve of coefficient of friction at 100 microm was formed as asine wave with clipped peaks which indicates the full slidebetween frictional pairs

33 Fretting Loop In most of the theoretical and experi-mental works the decisions of fretting regime and degra-dation mechanisms are made based on the ldquofretting looprdquowhich is defined by ldquoforce-displacementrdquo curve [3 5 6 9ndash12]Figure 9 shows the comparative Ft-D curves for partial andgross slip at the onset (after 5min) and the end (after 90min)of the fretting test e partially closed and elliptical curve

4 Advances in Materials Science and Engineering

which corresponds to PSR was obtained for 40 microm inFigure 9(a) However due to the continuation of cyclic loadsthe central mechanical interlocking was reduced and theclosed part of the loop was slightly widened after 90minis situation is related to the transition from primary elasticto plastic shear form and also due to the limited relative slipand small surface modification at higher normal loadParallelogram Ft-D curves at 100 microm attributed to GSRwhere displacement amplitude and thus the area of dissi-pated energy in the contact interface were greater In thiscase full sliding prevailed in the whole contact interfaceresulting in a higher rate of particle detachment and relativemotions were predominantly accommodated by plasticdeformation of counter surfaces during the entire fretting

processe fretting loop was kept almost unchanged for therest of the tests Besides fretting regimes according to theslip index criterion were also confirmed which can be cal-culated as shown in Figure 1(b) and δ found to be 056 forPSR while δ 106 for GSR both cases satisfying thetransition restrictions for slip index

34 Worn Scar Morphology e consequences of thesementioned frictional effects on the Inconel X-750 alloy andGCr15 steel ball specimens were investigated for partial andgross slip conditions by observing SEM morphologiesFigure 10 shows the damage evolutions on the flat material atthe stick and slip domains when the displacement amplitude

D = 40microm D = 100microm

(a)

D = 40microm D = 100microm

(b)

D = 40microm D = 100microm

(c)

Figure 3 SEM images of worn scars on Inconel X-750 alloy after (a) 10 (b) 30 and (c) 90minutes of fretting tests Double arrow indicatesfretting direction

Advances in Materials Science and Engineering 5

at 40 microm It was found that PSR was dominant in the contactarea with the mechanical interlocking of the asperities in thecontact center and adhered fretting scars due to themicroslips in the contact annulus However the degree ofthese degradation mechanisms was changing over thenumber of fretting cycles For instance Figure 10(a) showsthe fretting scars after 10min with limited material damagethe stick domain was smooth and surrounded by tiny pitsdue to the ratcheting eect In the later stages of frettingcycles (9times104) manymicrocracks surrounded the shrinkingstick area while the long crack perpendicular to the frettingdirection appeared in the contact border which looks like inthe stage of delamination process (Figure 10(b)) Further-more the sign of thick layer of material removal by harderGCr15 ball was observed in the slip region copye contactcenter was slowly worn out during the further fretting test by

overstressing and the wear mode was completely changedafter a considerable number of cycles (27times105) as shown inFigure 10(c) where the stick domain was totally rough andcovered with radial microcracks which were induced byfretting fatigue On the other hand the longer crack wasdetected along the far end of the contact which was partiallylled with wear debriscopye slip region also has been changedsince the previous condition where some layer of the an-nulus was transferred by opposite surface and this time theremaining layers of the contact annulus was removed byfurther cyclic stress which was assumed to be the exhaustionof ductility due to the plasticity accumulation by ratcheting

SEM morphologies in Figure 11 shows that the wholecontact interface was in full slide at 100 microm and degradationmechanisms were associated with adhesion abrasion de-lamination oxidation and plastic deformation as well as

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

μm

μm

0

5

10

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

(a)

μm

μm

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

ndash25

ndash30

ndash20

ndash15

ndash10

ndash5

0

5

10

(b)

μm

μm

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

5

10

(c)

Figure 4 Superimposed cross-section proles of wear scars perpendicular to the fretting direction through fretting time (a) After10minutes (b) After 30minutes (c) After 90minutes

6 Advances in Materials Science and Engineering

third-body flow between contact surfaces Red-brown oxi-dized powders were ejected from contact surfaces during thefretting process which can serve as abrasive particles prior totheir expulsion For example Figure 11(a) shows the wearmode onset of the fretting process in the contact centerwhere plowing grooves parallel to the sliding direction was

formed due to the larger relative motion by abrasive par-ticles followed by plastic shearing so that thick layers ofX-750 alloy were peeled off by adhesion Adhesive wear isoften occurred at the onset of fretting when friction pairscome into contact followed by plastic shearing that plucksoff the ends of the softer asperities is phenomenon is also

(a)

(b)

(c)

Figure 5 Surface topographies of worn scars for (a) 40 microm (left) and 100 microm (right) after 90minutes of fretting test (b) correspondingpreprocessed input area and (c) selected worn area to calculate the wear volume

Advances in Materials Science and Engineering 7

150

125

100W

ear v

olum

e los

s (lowast

106 micro

m3 )

75

50

25

0040

Displacement amplitude (microm)100

Aer 10 minutesAer 30 minutesAer 90 minutes

(a)

24

21

18

15

12

9

6

3

0

Wor

n sc

ar ar

ea (lowast

104 micro

m2 )

Displacement amplitude (microm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(b)

900

750

600

450

300

150

0

Wea

r rat

e (μm

3 mm

)

Displacement amplitude (μm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(c)

Figure 6 Calculated wear volumes (a) worn scar areas (b) and wear rates (c) after dierent time of fretting

00

02

04

06

08

10

12

0 600 1200 1800 2400 3000Time (s)

Coeffi

cien

t of f

rictio

n

3600 4200 4800 5400

40 microm100 microm

Figure 7 Coeordfcient of friction for contact pairs as a function of time

8 Advances in Materials Science and Engineering

attributed to galling and scuordfng [13] Figure 11(b) shows themagnied image in Figure 11(a) that the crack propagationswere prevented by particle detachment and started to spall

eventually becoming loose wear debris Fretted surfaces wererough owing to the plastic deformation and ploughing ef-fects and in some cases surface roughening would provide

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(a)

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(b)

Figure 9 Evolution of fretting loops for 40 microm and 100 microm after (a) 5 and (b) 90minutes of fretting

125100075050025000

ndash025ndash050ndash075ndash100ndash125

60001 60002 60003Time (s)

Coef

ficie

nt o

f fric

tion

60004 60005

40microm

(a)

Time (s)

125100075050025000

ndash025ndash050ndash075ndash100ndash125

Coef

ficie

nt o

f fric

tion

100microm

60001 60002 60003 60004 60005

(b)

Figure 8 Sinusoidal coeordfcient of frictions during 600 s fretting time for (a) 40 microm and (b) 100 microm

Advances in Materials Science and Engineering 9

escape channels for wear debris As the fretting test con-tinued the contact interfaces were slowly accommodated bythe plastic flow and further loading promoted the growth ofsubsurface cracks that parallel to the surface When thesecracks finally extended out to the free surface thin platelet-like wear particles delaminated as shown in Figures 11(c)and 11(d) In the same time when the delamination wasoccurring mostly in the contact center plastic flow of thecontacting surfaces in the periphery and third-body flowclose to the contact border were observed in Figures 11(e)and 11(f) respectively Moreover as temperature increasesbecause of frictional heating during GSR oxidation of thewear particles becomes more ubiquitous and as a

consequence thicker more continuous oxide layer will begenerated e greater contact temperature at this conditionalso causes plastic flow of the oxide film leading to moresevere oxidational wear [19]

Figure 12 shows the SEM images of wear scars andcorresponding 3D surface topographies of the steel ballsoscillated at 40 microm and 100 microm after 90minutes of frettingBoth wear scars were in a circular shape e worn surfacearea which was oscillated at 40 microm also contains the stickdomain in the contact center and slip domain at the pe-riphery as shown in Figure 12(a) However it is clear fromthe picture that a bulk of oxidized X-750 alloy surface layerin black was adhered to the half annulus of the contact which

Slip region

Stick region

Micropitboundary

Slip region

Adhesive microslip

(a)

Stick region

Microcracks

Slip region

Adhesive layerremoval

Crack delamination

(b)

Stick region

Cracks

Slip region

New crack growth alongthe contact border

(c)

Figure 10 SEMmicrographs of Inconel X-750 wear scars during PSR (a) after 10minutes (b) after 30minutes and (c) after 90minutes offretting Displacement amplitude is 40 microm Double arrows represent fretting direction

10 Advances in Materials Science and Engineering

was believed to be plucked off by harder GCr15 ball surfaceduring fretting induced by fatigue According to the wearscar in Figure 12(b) GSR was dominant at 100 microm with thesign of abrasion and small amount of transferred materialson the worn surface Figure 13 shows the EDX spectruminformation for the marked spots in Figure 12 on the wearscar areas Oxide content was very low (146 wt) in thestick region due to the constriction of the relative motionwhile microslip region was reacting with the oxygen in asmall amount On the other hand the highly concentratedoxygen content (29 wt) was detected on the transferredflat material in Figure 13(c) However the oxidation process

on the worn steel surface was faster during GSR rather thanPSR (Figure 13(d))

4 Discussion

e fretting wear process in an ambient temperature is oftendetermined by the contact geometry the oxidation processand the subsequent third-body behavior in the contact in-terface which significantly affect the friction and wearproperties in dry air [11 16 27] Wear properties such asvolume scar area and depth were considerably lowerduring PSR than GSR as shown in Figures 3ndash6 because of

(b)

Adhesive shear

Plowing

(a)

Crack spalling

(b)

Delamination

(c)

Delamination

Oxide layers

(d)

Plastic flow

(e)

Oxidized third-body flow

(f )

Figure 11 SEMmicrographs of Inconel X-750 wear scars during GSR (a) mixed abrasive and adhesive wear at the onset of fretting process(b) spalling of cracks (c d) delamination (e) plastic flow and (f) third-body flow near contact border Displacement amplitude is 100 micromDouble arrows represent fretting direction

Advances in Materials Science and Engineering 11

the small imposed contact area compared to the scale of thenormal load applied Yet the wear rate was maximum in therunning-in period for both cases decreasing gradually withfretting time in Figure 6(c) typically due to the formation ofthe oxide layer (also ldquoglazerdquo layer) on the worn surface which

can enhance the load-carrying capacity avoiding furtherwear [28] During the partial and gross slip conditions thefriction is the outcome of the direct interlocking of thesurface asperities and the trapped oxide debris behavior inthe contact interface respectively In Figure 7 the COF

Highly oxidized Inconel X-750alloy wear layer transfer

a b c

(a)

d

Oxidization

(b)

Figure 12 SEM morphologies of GCr15 steel ball worn scars oscillating at (a) 40 microm and (b) 100 microm Fretting time is 90minutes Doublearrows represent fretting direction

C

O

Fe

Ni SiPt CrMn

Fe

Ni

O KCr KFe KNi K

Element0653wt

019687490056

1888at

017572460044

00

06

12

17

23

29

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(a)

CO

Fe

NiSiPt Cr Mn

Fe

Ni

O KCr KFe KNi K

Element0146wt

026391270104

0470at

026184190091

200 300 400 500 600 700 800 900 10100Energy (keV)

00

05

10

16

21

26

KCnt

(b)

O KCr KFe KNi K

Element2959wt

107305115105

5793at

064702732863

C

O

FeNi SiPt

Cr

Mn Fe

Ni

00

06

12

18

24

30

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(c)

O KCr KFe KNi K

Element1499wt

020378570071

3572at

014953640046

C

O

FeNi

SiPt CrMn

Fe

Ni

200 300 400 500 600 700 800 900 10100Energy (keV)

00

04

09

13

18

22

KCnt

(d)

Figure 13 EDX spectroscopy analysis for worn surfaces at marked spots in Figure 12

12 Advances in Materials Science and Engineering

during PSR was always lower with no apparent fluctuationduring the steady-stage level due to the minimum tangentialforce between the contact interfaces where the central zoneswere mechanically interlocked In this case the highernormal load triggers the traction coefficient where thecritical total sliding shear force is always higher than thetangential force [5 11] However in GSR the highest peak offriction occurred prior to the fluctuating steady-stage levelmainly due to the strong plastic deformation of work-hardened layer of the contacting surfaces [23 29] On theother hand the fluctuations in COF are attributed to themodifications in the contact interface which are linked to thethird-body rheology ie wear debris formation and itsentrapment and ejection from the contact zone [27]

e fretting loops generated by Ft-D curves in Figure 9are good indicators to show the slip condition at any mo-ment e area enclosed by the curves is the measure ofdissipated energy produced by friction [10 30] e frictionwork performed provides a more representative explanationof the surface damage Usually it has been noticed that thewear volume V is proportional to the energy dissipated Edin the contact and described as V αtimes 1113936Ed where α is thefriction energy wear coefficient [6] e degree of slope Sccan be considered as wear characteristics of the slidingconditions and materials Besides the unified slip indexapproach also offers the knowledge of fretting conditionsand considered as an appropriate means for estimatingfretting wear problems In accordance with the terms of slipindex when the slip ratio s⟶ 0 the contacts are in stickand as the slip ratio approaches to 1 partial slip and thengross slip prevail [2] e partial slip contacts in smalldisplacements induce cyclic stresses which favor cracknucleation and propagation but the loading condition isnondissipative with limited surface damage at the peripheryas shown in Figure 10 However the friction dissipation inGSR correlated with the plastic flow delamination andoxidation wear mechanisms causes a large amount ofsurface damage by extending the contact area and reducingthe contact pressure profile (Figure 11)

e main damage mechanisms ie cracking (frettinginduced by fatigue) and material loss (fretting induced bywear) are often appear as a competing process which wasextensively explored during the last decade [1 3 5 6 31ndash34]For instance the material loss during GSR can eliminatesmall cracks or fill up the opening of a deep crack andaccommodate the main portion of the imposed displace-ment as a consequence it strongly reduces the slip am-plitude and then the debris formation In fact the debrisejection has great impact on the third-body establishment ifit is trapped between the contacts the degradation processcan be suppressed and the most of the velocity differencebetween the friction pairs would be completely accommo-dated in a dissipative manner by the powder bed [33 34] Asfor cracking the effects of frictional force and the contactload are huge on the crack initiation and growth duringfretting fatigue where the frictional force triggers the crackinitiation while the contact load disrupts the crack growthduring the propagation period [37] Meanwhile it is re-ported that the cracks on the worn scar surface nucleated

and propagated along the direction of 30ndash50deg to the surfaceinterior which was in the range of calculated maximumshear stress angle [18]

SEM morphology in Figure 12(a) shows the interestingwear phenomenon where the thick layer of Inconel X-750alloy was stuck to the worn surface of the oscillating ball dueto the adhesive microslip In return with the further frettingthe material transferred to the surface of GCr14 ball has thehighest possibility to transfer back to the previous wornsurface of Inconel X-750 alloy [8] Besides the transferredwear layer was highly oxidized compared to the stick and slipregions of the steel ball as shown in Figure 13 e debrisdetached from the contact pairs is essentially composed ofnonmagnetic single component oxides eg Fe2O3 NiO andCr2O3 or more complex oxides eg NiCr2O4 and NiFe2O4[38] However the oxidization process was rapid on theworn surface of the steel ball during GSR which is because ofmore mechanical energy being converted to the thermalheat and it is believed that the frictional heat during GSRwas higher than in PSR [19]

5 Conclusion

e main purpose of this study was to explore the degra-dation evolutions of Inconel X-750 co-acted with GCr15steel ball through the dry fretting tests and observationsanalyses by using 3D surface profiler SEM and EDXAccording to the results the conclusions can be drawn asfollows

(i) e degradation mechanisms of Inconel X-750 weretotally dependent on the fretting regimes and variedwith the fretting time

(ii) e wear volume and wear depth were very low inPSR and wear mechanisms were associated with thedeformations adhesion and fatigue crack emicrocracks were present around the stick domainin 3times104 cycle and the radial cracks fully coveredthe contact center above 105 cycle along with thebigger crack in the contact border e large layer ofductile X-750 alloy was transferred to the wearsurface of the steel ball due to the exhaustion byhighly concentrated cyclic loading during the laterstages of fretting

(iii) In GSR the degradation mechanisms were as fol-lows (1) adhesive wear (galling and scuffing) (2)abrasive wear by third-body particle which is amechanical removal process (3) delaminationwhich is influenced by the material fatigue in theshallow subsurface layer and (4) oxidation of debrisparticles and surface layer due to the higher fric-tional heat which can enhance the load-carryingcapacity as well as reduce the wear rate in the laterstages of fretting process

(iv) e dependence of fretting time was negligibleduring PSR in respect of wear properties such aswear volume scar area and depth However it has agreat impact to evolve the degradation mechanisms

Advances in Materials Science and Engineering 13

from asperity deformation to the crack initiationand propagation which is a critical damage duringPSR On the other hand the wear volume and scararea were increased significantly by time duringGSR but the degradation evolutions were combinedand repeated with the mentioned wear mechanismsin a whole fretting process

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

e first author would like to acknowledge the scholarshipsupport from China Scholarship Council (CSC) is workwas supported by the Aeronautical Science Fund of China(Grant no 20164058002) National Natural Science Foun-dation of China (Grant No51735006) and Tsinghua Uni-versity Initiative Scientific Research Program

References

[1] R B Waterhouse ldquoFretting wearrdquo Wear vol 100 no 1ndash3pp 107ndash118 1984

[2] M Varenberg I Etsion and G Halperin ldquoSlip index a newunified approach to frettingrdquo Tribology Letters vol 17 no 3pp 569ndash573 2004

[3] O Vingsbo and S Soderberg ldquoOn fretting mapsrdquo Wearvol 126 no 2 pp 131ndash147 1988

[4] R D Mindlin and H Deresiewiez ldquoElastic spheres in contactunder varying oblique forcesrdquo Journal of Applied Mechanicsvol 20 pp 327ndash344 1953

[5] Z R Zhou and L Vincent ldquoMixed fretting regimerdquo Wearvol 181ndash183 pp 531ndash536 1995

[6] S Fouvry P Kapsa and L Vincent ldquoQuantification offretting damagerdquo Wear vol 200 no 1-2 pp 186ndash205 1996

[7] J Yu L Qian B Yu and Z Zhou ldquoNanofretting behavior ofmonocrystalline silicon (100) against SiO2 microsphere invacuumrdquo Tribology Letters vol 34 no 1 pp 31ndash40 2009

[8] H Mohrbacher J P Celis and J R Roos ldquoLaboratory testingof displacement and load induced frettingrdquo Tribology In-ternational vol 28 no 5 pp 269ndash278 1995

[9] Z R Zhou S Fayeulle and L Vincent ldquoCracking behaviourof various aluminium alloys during fretting wearrdquo Wearvol 155 no 2 pp 317ndash330 1992

[10] S Fouvry P Kapsa H Zahouani and L Vincent ldquoWearanalysis in fretting of hard coatings through a dissipatedenergy conceptrdquo Wear vol 203-204 pp 393ndash403 1997

[11] J Li and Y H Lu ldquoEffects of displacement amplitude onfretting wear behaviors and mechanism of Inconel 600 alloyrdquoWear vol 304 no 1-2 pp 223ndash230 2013

[12] G B Stachowiak and G W Stachowiak ldquoFretting wear andfriction behaviour of engineering ceramicsrdquo Wear vol 190no 2 pp 212ndash218 1995

[13] B Bhushan and B K Gupta Handbook of Tribology Mate-rials Coatings and Surface Treatments McGraw-Hill NewYork NY USA 1991

[14] H Y Zhang Y H Lu M Ma and J Li ldquoEffect of precipitatedcarbides on the fretting wear behavior of Inconel 600 alloyrdquoWear vol 315 no 1-2 pp 58ndash67 2014

[15] X Mi W X Wang X M Xiong et al ldquoInvestigation offretting wear behavior of Inconel 690 alloy in tubeplatecontact configurationrdquoWear vol 328-329 pp 582ndash590 2015

[16] L Jie L Yonghao Z Haoyang and L Xin ldquoEffect of grain sizeand hardness on fretting wear behavior of inconel 600 alloysrdquoTribology International vol 81 pp 215ndash222 2015

[17] L Xin B B Yang Z H Wang J Li Y H Lu and T ShojildquoMicrostructural evolution of subsurface on inconel 690TTalloy subjected to fretting wear at elevated temperaturerdquoMaterials amp Design vol 104 pp 152ndash161 2016

[18] J Li B B Yang Y H Lu L Xin Z H Wang and T Shojildquoe degradation mechanism of inconel 690TT induced byfretting wear in airrdquo Tribology International vol 116pp 147ndash154 2017

[19] G Xianglong L Ping T Lichen et al ldquoEffects of slidingamplitude and normal load on the fretting wear behavior ofalloy 690 tube exposed to high temperature waterrdquo TribologyInternational vol 116 pp 155ndash163 2017

[20] Special Metals INCONEL alloy X-750 Data Sheet 2004Publication No SMC-067 httpwwwspecialmetalscom

[21] C Marsh S Depinoy and D Kaoumi ldquoEffect of heattreatment on the temperature dependence of the fracturebehavior of X-750 alloyrdquo Materials Science and EngineeringA vol 677 pp 474ndash484 2016

[22] D Wenbo S Yanhua D Chunhua and Y Lie ldquoStructuralstiffness of X-750 alloy bump foil strips for compliant foilbearings with different heat treatmentsrdquo Journal of Tribologyvol 138 no 3 article 031702 2016

[23] G X Chen and Z R Zhou ldquoStudy on transition betweenfretting and reciprocating sliding wearrdquo Wear vol 250no 1ndash12 pp 665ndash672 2001

[24] J F Archard ldquoContact and rubbing of flat surfacesrdquo Journal ofApplied Physics vol 24 no 8 pp 981ndash988 1953

[25] S C Lim M F Ashby and J H Brunton ldquoWear-ratetransitions and their relationship to wear mechanismsrdquoActa Metallurgica vol 35 no 6 pp 1343ndash1348 1987

[26] S C Lim ldquoRecent developments in wear-mechanism mapsrdquoTribology International vol 31 no 1ndash3 pp 87ndash97 1998

[27] X LongW Zihao L Jie Y Lu and T Shoji ldquoMicrostructuralcharacterization of subsurface caused by fretting wear ofinconel 690TT alloyrdquo Material Characteristics vol 115pp 32ndash38 2016

[28] R Rybiak S Fouvry and B Bonnet ldquoFretting wear of stainlesssteels under variable temperature conditions introduction ofa ldquocompositerdquo wear lawrdquoWear vol 268 no 3-4 pp 413ndash4232010

[29] J F Zheng J Luo J L Mo J F Peng X S Jin andMH ZhuldquoFretting wear behaviors of a railway axle steelrdquo TribologyInternational vol 43 no 5-6 pp 906ndash911 2010

[30] K V Virendra N Hamza S S R Ganesh H MurthyA N Majila and D C Fernando ldquoEffect of contact pressureand stress ratio on the fretting fatigue behaviour of Ti-6Al-4Vrdquo Material Science and Engineering A vol 707 pp 647ndash656 2017

[31] J J Madge S B Leen and P H Shipway ldquoe critical role offretting wear in the analysis of fretting fatiguerdquoWear vol 263no 1ndash6 pp 542ndash551 2007

14 Advances in Materials Science and Engineering

which corresponds to PSR was obtained for 40 microm inFigure 9(a) However due to the continuation of cyclic loadsthe central mechanical interlocking was reduced and theclosed part of the loop was slightly widened after 90minis situation is related to the transition from primary elasticto plastic shear form and also due to the limited relative slipand small surface modification at higher normal loadParallelogram Ft-D curves at 100 microm attributed to GSRwhere displacement amplitude and thus the area of dissi-pated energy in the contact interface were greater In thiscase full sliding prevailed in the whole contact interfaceresulting in a higher rate of particle detachment and relativemotions were predominantly accommodated by plasticdeformation of counter surfaces during the entire fretting

processe fretting loop was kept almost unchanged for therest of the tests Besides fretting regimes according to theslip index criterion were also confirmed which can be cal-culated as shown in Figure 1(b) and δ found to be 056 forPSR while δ 106 for GSR both cases satisfying thetransition restrictions for slip index

34 Worn Scar Morphology e consequences of thesementioned frictional effects on the Inconel X-750 alloy andGCr15 steel ball specimens were investigated for partial andgross slip conditions by observing SEM morphologiesFigure 10 shows the damage evolutions on the flat material atthe stick and slip domains when the displacement amplitude

D = 40microm D = 100microm

(a)

D = 40microm D = 100microm

(b)

D = 40microm D = 100microm

(c)

Figure 3 SEM images of worn scars on Inconel X-750 alloy after (a) 10 (b) 30 and (c) 90minutes of fretting tests Double arrow indicatesfretting direction

Advances in Materials Science and Engineering 5

at 40 microm It was found that PSR was dominant in the contactarea with the mechanical interlocking of the asperities in thecontact center and adhered fretting scars due to themicroslips in the contact annulus However the degree ofthese degradation mechanisms was changing over thenumber of fretting cycles For instance Figure 10(a) showsthe fretting scars after 10min with limited material damagethe stick domain was smooth and surrounded by tiny pitsdue to the ratcheting eect In the later stages of frettingcycles (9times104) manymicrocracks surrounded the shrinkingstick area while the long crack perpendicular to the frettingdirection appeared in the contact border which looks like inthe stage of delamination process (Figure 10(b)) Further-more the sign of thick layer of material removal by harderGCr15 ball was observed in the slip region copye contactcenter was slowly worn out during the further fretting test by

overstressing and the wear mode was completely changedafter a considerable number of cycles (27times105) as shown inFigure 10(c) where the stick domain was totally rough andcovered with radial microcracks which were induced byfretting fatigue On the other hand the longer crack wasdetected along the far end of the contact which was partiallylled with wear debriscopye slip region also has been changedsince the previous condition where some layer of the an-nulus was transferred by opposite surface and this time theremaining layers of the contact annulus was removed byfurther cyclic stress which was assumed to be the exhaustionof ductility due to the plasticity accumulation by ratcheting

SEM morphologies in Figure 11 shows that the wholecontact interface was in full slide at 100 microm and degradationmechanisms were associated with adhesion abrasion de-lamination oxidation and plastic deformation as well as

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

μm

μm

0

5

10

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

(a)

μm

μm

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

ndash25

ndash30

ndash20

ndash15

ndash10

ndash5

0

5

10

(b)

μm

μm

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

5

10

(c)

Figure 4 Superimposed cross-section proles of wear scars perpendicular to the fretting direction through fretting time (a) After10minutes (b) After 30minutes (c) After 90minutes

6 Advances in Materials Science and Engineering

third-body flow between contact surfaces Red-brown oxi-dized powders were ejected from contact surfaces during thefretting process which can serve as abrasive particles prior totheir expulsion For example Figure 11(a) shows the wearmode onset of the fretting process in the contact centerwhere plowing grooves parallel to the sliding direction was

formed due to the larger relative motion by abrasive par-ticles followed by plastic shearing so that thick layers ofX-750 alloy were peeled off by adhesion Adhesive wear isoften occurred at the onset of fretting when friction pairscome into contact followed by plastic shearing that plucksoff the ends of the softer asperities is phenomenon is also

(a)

(b)

(c)

Figure 5 Surface topographies of worn scars for (a) 40 microm (left) and 100 microm (right) after 90minutes of fretting test (b) correspondingpreprocessed input area and (c) selected worn area to calculate the wear volume

Advances in Materials Science and Engineering 7

150

125

100W

ear v

olum

e los

s (lowast

106 micro

m3 )

75

50

25

0040

Displacement amplitude (microm)100

Aer 10 minutesAer 30 minutesAer 90 minutes

(a)

24

21

18

15

12

9

6

3

0

Wor

n sc

ar ar

ea (lowast

104 micro

m2 )

Displacement amplitude (microm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(b)

900

750

600

450

300

150

0

Wea

r rat

e (μm

3 mm

)

Displacement amplitude (μm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(c)

Figure 6 Calculated wear volumes (a) worn scar areas (b) and wear rates (c) after dierent time of fretting

00

02

04

06

08

10

12

0 600 1200 1800 2400 3000Time (s)

Coeffi

cien

t of f

rictio

n

3600 4200 4800 5400

40 microm100 microm

Figure 7 Coeordfcient of friction for contact pairs as a function of time

8 Advances in Materials Science and Engineering

attributed to galling and scuordfng [13] Figure 11(b) shows themagnied image in Figure 11(a) that the crack propagationswere prevented by particle detachment and started to spall

eventually becoming loose wear debris Fretted surfaces wererough owing to the plastic deformation and ploughing ef-fects and in some cases surface roughening would provide

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(a)

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(b)

Figure 9 Evolution of fretting loops for 40 microm and 100 microm after (a) 5 and (b) 90minutes of fretting

125100075050025000

ndash025ndash050ndash075ndash100ndash125

60001 60002 60003Time (s)

Coef

ficie

nt o

f fric

tion

60004 60005

40microm

(a)

Time (s)

125100075050025000

ndash025ndash050ndash075ndash100ndash125

Coef

ficie

nt o

f fric

tion

100microm

60001 60002 60003 60004 60005

(b)

Figure 8 Sinusoidal coeordfcient of frictions during 600 s fretting time for (a) 40 microm and (b) 100 microm

Advances in Materials Science and Engineering 9

escape channels for wear debris As the fretting test con-tinued the contact interfaces were slowly accommodated bythe plastic flow and further loading promoted the growth ofsubsurface cracks that parallel to the surface When thesecracks finally extended out to the free surface thin platelet-like wear particles delaminated as shown in Figures 11(c)and 11(d) In the same time when the delamination wasoccurring mostly in the contact center plastic flow of thecontacting surfaces in the periphery and third-body flowclose to the contact border were observed in Figures 11(e)and 11(f) respectively Moreover as temperature increasesbecause of frictional heating during GSR oxidation of thewear particles becomes more ubiquitous and as a

consequence thicker more continuous oxide layer will begenerated e greater contact temperature at this conditionalso causes plastic flow of the oxide film leading to moresevere oxidational wear [19]

Figure 12 shows the SEM images of wear scars andcorresponding 3D surface topographies of the steel ballsoscillated at 40 microm and 100 microm after 90minutes of frettingBoth wear scars were in a circular shape e worn surfacearea which was oscillated at 40 microm also contains the stickdomain in the contact center and slip domain at the pe-riphery as shown in Figure 12(a) However it is clear fromthe picture that a bulk of oxidized X-750 alloy surface layerin black was adhered to the half annulus of the contact which

Slip region

Stick region

Micropitboundary

Slip region

Adhesive microslip

(a)

Stick region

Microcracks

Slip region

Adhesive layerremoval

Crack delamination

(b)

Stick region

Cracks

Slip region

New crack growth alongthe contact border

(c)

Figure 10 SEMmicrographs of Inconel X-750 wear scars during PSR (a) after 10minutes (b) after 30minutes and (c) after 90minutes offretting Displacement amplitude is 40 microm Double arrows represent fretting direction

10 Advances in Materials Science and Engineering

was believed to be plucked off by harder GCr15 ball surfaceduring fretting induced by fatigue According to the wearscar in Figure 12(b) GSR was dominant at 100 microm with thesign of abrasion and small amount of transferred materialson the worn surface Figure 13 shows the EDX spectruminformation for the marked spots in Figure 12 on the wearscar areas Oxide content was very low (146 wt) in thestick region due to the constriction of the relative motionwhile microslip region was reacting with the oxygen in asmall amount On the other hand the highly concentratedoxygen content (29 wt) was detected on the transferredflat material in Figure 13(c) However the oxidation process

on the worn steel surface was faster during GSR rather thanPSR (Figure 13(d))

4 Discussion

e fretting wear process in an ambient temperature is oftendetermined by the contact geometry the oxidation processand the subsequent third-body behavior in the contact in-terface which significantly affect the friction and wearproperties in dry air [11 16 27] Wear properties such asvolume scar area and depth were considerably lowerduring PSR than GSR as shown in Figures 3ndash6 because of

(b)

Adhesive shear

Plowing

(a)

Crack spalling

(b)

Delamination

(c)

Delamination

Oxide layers

(d)

Plastic flow

(e)

Oxidized third-body flow

(f )

Figure 11 SEMmicrographs of Inconel X-750 wear scars during GSR (a) mixed abrasive and adhesive wear at the onset of fretting process(b) spalling of cracks (c d) delamination (e) plastic flow and (f) third-body flow near contact border Displacement amplitude is 100 micromDouble arrows represent fretting direction

Advances in Materials Science and Engineering 11

the small imposed contact area compared to the scale of thenormal load applied Yet the wear rate was maximum in therunning-in period for both cases decreasing gradually withfretting time in Figure 6(c) typically due to the formation ofthe oxide layer (also ldquoglazerdquo layer) on the worn surface which

can enhance the load-carrying capacity avoiding furtherwear [28] During the partial and gross slip conditions thefriction is the outcome of the direct interlocking of thesurface asperities and the trapped oxide debris behavior inthe contact interface respectively In Figure 7 the COF

Highly oxidized Inconel X-750alloy wear layer transfer

a b c

(a)

d

Oxidization

(b)

Figure 12 SEM morphologies of GCr15 steel ball worn scars oscillating at (a) 40 microm and (b) 100 microm Fretting time is 90minutes Doublearrows represent fretting direction

C

O

Fe

Ni SiPt CrMn

Fe

Ni

O KCr KFe KNi K

Element0653wt

019687490056

1888at

017572460044

00

06

12

17

23

29

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(a)

CO

Fe

NiSiPt Cr Mn

Fe

Ni

O KCr KFe KNi K

Element0146wt

026391270104

0470at

026184190091

200 300 400 500 600 700 800 900 10100Energy (keV)

00

05

10

16

21

26

KCnt

(b)

O KCr KFe KNi K

Element2959wt

107305115105

5793at

064702732863

C

O

FeNi SiPt

Cr

Mn Fe

Ni

00

06

12

18

24

30

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(c)

O KCr KFe KNi K

Element1499wt

020378570071

3572at

014953640046

C

O

FeNi

SiPt CrMn

Fe

Ni

200 300 400 500 600 700 800 900 10100Energy (keV)

00

04

09

13

18

22

KCnt

(d)

Figure 13 EDX spectroscopy analysis for worn surfaces at marked spots in Figure 12

12 Advances in Materials Science and Engineering

during PSR was always lower with no apparent fluctuationduring the steady-stage level due to the minimum tangentialforce between the contact interfaces where the central zoneswere mechanically interlocked In this case the highernormal load triggers the traction coefficient where thecritical total sliding shear force is always higher than thetangential force [5 11] However in GSR the highest peak offriction occurred prior to the fluctuating steady-stage levelmainly due to the strong plastic deformation of work-hardened layer of the contacting surfaces [23 29] On theother hand the fluctuations in COF are attributed to themodifications in the contact interface which are linked to thethird-body rheology ie wear debris formation and itsentrapment and ejection from the contact zone [27]

e fretting loops generated by Ft-D curves in Figure 9are good indicators to show the slip condition at any mo-ment e area enclosed by the curves is the measure ofdissipated energy produced by friction [10 30] e frictionwork performed provides a more representative explanationof the surface damage Usually it has been noticed that thewear volume V is proportional to the energy dissipated Edin the contact and described as V αtimes 1113936Ed where α is thefriction energy wear coefficient [6] e degree of slope Sccan be considered as wear characteristics of the slidingconditions and materials Besides the unified slip indexapproach also offers the knowledge of fretting conditionsand considered as an appropriate means for estimatingfretting wear problems In accordance with the terms of slipindex when the slip ratio s⟶ 0 the contacts are in stickand as the slip ratio approaches to 1 partial slip and thengross slip prevail [2] e partial slip contacts in smalldisplacements induce cyclic stresses which favor cracknucleation and propagation but the loading condition isnondissipative with limited surface damage at the peripheryas shown in Figure 10 However the friction dissipation inGSR correlated with the plastic flow delamination andoxidation wear mechanisms causes a large amount ofsurface damage by extending the contact area and reducingthe contact pressure profile (Figure 11)

e main damage mechanisms ie cracking (frettinginduced by fatigue) and material loss (fretting induced bywear) are often appear as a competing process which wasextensively explored during the last decade [1 3 5 6 31ndash34]For instance the material loss during GSR can eliminatesmall cracks or fill up the opening of a deep crack andaccommodate the main portion of the imposed displace-ment as a consequence it strongly reduces the slip am-plitude and then the debris formation In fact the debrisejection has great impact on the third-body establishment ifit is trapped between the contacts the degradation processcan be suppressed and the most of the velocity differencebetween the friction pairs would be completely accommo-dated in a dissipative manner by the powder bed [33 34] Asfor cracking the effects of frictional force and the contactload are huge on the crack initiation and growth duringfretting fatigue where the frictional force triggers the crackinitiation while the contact load disrupts the crack growthduring the propagation period [37] Meanwhile it is re-ported that the cracks on the worn scar surface nucleated

and propagated along the direction of 30ndash50deg to the surfaceinterior which was in the range of calculated maximumshear stress angle [18]

SEM morphology in Figure 12(a) shows the interestingwear phenomenon where the thick layer of Inconel X-750alloy was stuck to the worn surface of the oscillating ball dueto the adhesive microslip In return with the further frettingthe material transferred to the surface of GCr14 ball has thehighest possibility to transfer back to the previous wornsurface of Inconel X-750 alloy [8] Besides the transferredwear layer was highly oxidized compared to the stick and slipregions of the steel ball as shown in Figure 13 e debrisdetached from the contact pairs is essentially composed ofnonmagnetic single component oxides eg Fe2O3 NiO andCr2O3 or more complex oxides eg NiCr2O4 and NiFe2O4[38] However the oxidization process was rapid on theworn surface of the steel ball during GSR which is because ofmore mechanical energy being converted to the thermalheat and it is believed that the frictional heat during GSRwas higher than in PSR [19]

5 Conclusion

e main purpose of this study was to explore the degra-dation evolutions of Inconel X-750 co-acted with GCr15steel ball through the dry fretting tests and observationsanalyses by using 3D surface profiler SEM and EDXAccording to the results the conclusions can be drawn asfollows

(i) e degradation mechanisms of Inconel X-750 weretotally dependent on the fretting regimes and variedwith the fretting time

(ii) e wear volume and wear depth were very low inPSR and wear mechanisms were associated with thedeformations adhesion and fatigue crack emicrocracks were present around the stick domainin 3times104 cycle and the radial cracks fully coveredthe contact center above 105 cycle along with thebigger crack in the contact border e large layer ofductile X-750 alloy was transferred to the wearsurface of the steel ball due to the exhaustion byhighly concentrated cyclic loading during the laterstages of fretting

(iii) In GSR the degradation mechanisms were as fol-lows (1) adhesive wear (galling and scuffing) (2)abrasive wear by third-body particle which is amechanical removal process (3) delaminationwhich is influenced by the material fatigue in theshallow subsurface layer and (4) oxidation of debrisparticles and surface layer due to the higher fric-tional heat which can enhance the load-carryingcapacity as well as reduce the wear rate in the laterstages of fretting process

(iv) e dependence of fretting time was negligibleduring PSR in respect of wear properties such aswear volume scar area and depth However it has agreat impact to evolve the degradation mechanisms

Advances in Materials Science and Engineering 13

from asperity deformation to the crack initiationand propagation which is a critical damage duringPSR On the other hand the wear volume and scararea were increased significantly by time duringGSR but the degradation evolutions were combinedand repeated with the mentioned wear mechanismsin a whole fretting process

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

e first author would like to acknowledge the scholarshipsupport from China Scholarship Council (CSC) is workwas supported by the Aeronautical Science Fund of China(Grant no 20164058002) National Natural Science Foun-dation of China (Grant No51735006) and Tsinghua Uni-versity Initiative Scientific Research Program

References

[1] R B Waterhouse ldquoFretting wearrdquo Wear vol 100 no 1ndash3pp 107ndash118 1984

[2] M Varenberg I Etsion and G Halperin ldquoSlip index a newunified approach to frettingrdquo Tribology Letters vol 17 no 3pp 569ndash573 2004

[3] O Vingsbo and S Soderberg ldquoOn fretting mapsrdquo Wearvol 126 no 2 pp 131ndash147 1988

[4] R D Mindlin and H Deresiewiez ldquoElastic spheres in contactunder varying oblique forcesrdquo Journal of Applied Mechanicsvol 20 pp 327ndash344 1953

[5] Z R Zhou and L Vincent ldquoMixed fretting regimerdquo Wearvol 181ndash183 pp 531ndash536 1995

[6] S Fouvry P Kapsa and L Vincent ldquoQuantification offretting damagerdquo Wear vol 200 no 1-2 pp 186ndash205 1996

[7] J Yu L Qian B Yu and Z Zhou ldquoNanofretting behavior ofmonocrystalline silicon (100) against SiO2 microsphere invacuumrdquo Tribology Letters vol 34 no 1 pp 31ndash40 2009

[8] H Mohrbacher J P Celis and J R Roos ldquoLaboratory testingof displacement and load induced frettingrdquo Tribology In-ternational vol 28 no 5 pp 269ndash278 1995

[9] Z R Zhou S Fayeulle and L Vincent ldquoCracking behaviourof various aluminium alloys during fretting wearrdquo Wearvol 155 no 2 pp 317ndash330 1992

[10] S Fouvry P Kapsa H Zahouani and L Vincent ldquoWearanalysis in fretting of hard coatings through a dissipatedenergy conceptrdquo Wear vol 203-204 pp 393ndash403 1997

[11] J Li and Y H Lu ldquoEffects of displacement amplitude onfretting wear behaviors and mechanism of Inconel 600 alloyrdquoWear vol 304 no 1-2 pp 223ndash230 2013

[12] G B Stachowiak and G W Stachowiak ldquoFretting wear andfriction behaviour of engineering ceramicsrdquo Wear vol 190no 2 pp 212ndash218 1995

[13] B Bhushan and B K Gupta Handbook of Tribology Mate-rials Coatings and Surface Treatments McGraw-Hill NewYork NY USA 1991

[14] H Y Zhang Y H Lu M Ma and J Li ldquoEffect of precipitatedcarbides on the fretting wear behavior of Inconel 600 alloyrdquoWear vol 315 no 1-2 pp 58ndash67 2014

[15] X Mi W X Wang X M Xiong et al ldquoInvestigation offretting wear behavior of Inconel 690 alloy in tubeplatecontact configurationrdquoWear vol 328-329 pp 582ndash590 2015

[16] L Jie L Yonghao Z Haoyang and L Xin ldquoEffect of grain sizeand hardness on fretting wear behavior of inconel 600 alloysrdquoTribology International vol 81 pp 215ndash222 2015

[17] L Xin B B Yang Z H Wang J Li Y H Lu and T ShojildquoMicrostructural evolution of subsurface on inconel 690TTalloy subjected to fretting wear at elevated temperaturerdquoMaterials amp Design vol 104 pp 152ndash161 2016

[18] J Li B B Yang Y H Lu L Xin Z H Wang and T Shojildquoe degradation mechanism of inconel 690TT induced byfretting wear in airrdquo Tribology International vol 116pp 147ndash154 2017

[19] G Xianglong L Ping T Lichen et al ldquoEffects of slidingamplitude and normal load on the fretting wear behavior ofalloy 690 tube exposed to high temperature waterrdquo TribologyInternational vol 116 pp 155ndash163 2017

[20] Special Metals INCONEL alloy X-750 Data Sheet 2004Publication No SMC-067 httpwwwspecialmetalscom

[21] C Marsh S Depinoy and D Kaoumi ldquoEffect of heattreatment on the temperature dependence of the fracturebehavior of X-750 alloyrdquo Materials Science and EngineeringA vol 677 pp 474ndash484 2016

[22] D Wenbo S Yanhua D Chunhua and Y Lie ldquoStructuralstiffness of X-750 alloy bump foil strips for compliant foilbearings with different heat treatmentsrdquo Journal of Tribologyvol 138 no 3 article 031702 2016

[23] G X Chen and Z R Zhou ldquoStudy on transition betweenfretting and reciprocating sliding wearrdquo Wear vol 250no 1ndash12 pp 665ndash672 2001

[24] J F Archard ldquoContact and rubbing of flat surfacesrdquo Journal ofApplied Physics vol 24 no 8 pp 981ndash988 1953

[25] S C Lim M F Ashby and J H Brunton ldquoWear-ratetransitions and their relationship to wear mechanismsrdquoActa Metallurgica vol 35 no 6 pp 1343ndash1348 1987

[26] S C Lim ldquoRecent developments in wear-mechanism mapsrdquoTribology International vol 31 no 1ndash3 pp 87ndash97 1998

[27] X LongW Zihao L Jie Y Lu and T Shoji ldquoMicrostructuralcharacterization of subsurface caused by fretting wear ofinconel 690TT alloyrdquo Material Characteristics vol 115pp 32ndash38 2016

[28] R Rybiak S Fouvry and B Bonnet ldquoFretting wear of stainlesssteels under variable temperature conditions introduction ofa ldquocompositerdquo wear lawrdquoWear vol 268 no 3-4 pp 413ndash4232010

[29] J F Zheng J Luo J L Mo J F Peng X S Jin andMH ZhuldquoFretting wear behaviors of a railway axle steelrdquo TribologyInternational vol 43 no 5-6 pp 906ndash911 2010

[30] K V Virendra N Hamza S S R Ganesh H MurthyA N Majila and D C Fernando ldquoEffect of contact pressureand stress ratio on the fretting fatigue behaviour of Ti-6Al-4Vrdquo Material Science and Engineering A vol 707 pp 647ndash656 2017

[31] J J Madge S B Leen and P H Shipway ldquoe critical role offretting wear in the analysis of fretting fatiguerdquoWear vol 263no 1ndash6 pp 542ndash551 2007

14 Advances in Materials Science and Engineering

at 40 microm It was found that PSR was dominant in the contactarea with the mechanical interlocking of the asperities in thecontact center and adhered fretting scars due to themicroslips in the contact annulus However the degree ofthese degradation mechanisms was changing over thenumber of fretting cycles For instance Figure 10(a) showsthe fretting scars after 10min with limited material damagethe stick domain was smooth and surrounded by tiny pitsdue to the ratcheting eect In the later stages of frettingcycles (9times104) manymicrocracks surrounded the shrinkingstick area while the long crack perpendicular to the frettingdirection appeared in the contact border which looks like inthe stage of delamination process (Figure 10(b)) Further-more the sign of thick layer of material removal by harderGCr15 ball was observed in the slip region copye contactcenter was slowly worn out during the further fretting test by

overstressing and the wear mode was completely changedafter a considerable number of cycles (27times105) as shown inFigure 10(c) where the stick domain was totally rough andcovered with radial microcracks which were induced byfretting fatigue On the other hand the longer crack wasdetected along the far end of the contact which was partiallylled with wear debriscopye slip region also has been changedsince the previous condition where some layer of the an-nulus was transferred by opposite surface and this time theremaining layers of the contact annulus was removed byfurther cyclic stress which was assumed to be the exhaustionof ductility due to the plasticity accumulation by ratcheting

SEM morphologies in Figure 11 shows that the wholecontact interface was in full slide at 100 microm and degradationmechanisms were associated with adhesion abrasion de-lamination oxidation and plastic deformation as well as

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

μm

μm

0

5

10

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

(a)

μm

μm

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

ndash25

ndash30

ndash20

ndash15

ndash10

ndash5

0

5

10

(b)

μm

μm

0 200 400 600 800 1000 1200 1400 1600 1800

40μm100μm

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

5

10

(c)

Figure 4 Superimposed cross-section proles of wear scars perpendicular to the fretting direction through fretting time (a) After10minutes (b) After 30minutes (c) After 90minutes

6 Advances in Materials Science and Engineering

third-body flow between contact surfaces Red-brown oxi-dized powders were ejected from contact surfaces during thefretting process which can serve as abrasive particles prior totheir expulsion For example Figure 11(a) shows the wearmode onset of the fretting process in the contact centerwhere plowing grooves parallel to the sliding direction was

formed due to the larger relative motion by abrasive par-ticles followed by plastic shearing so that thick layers ofX-750 alloy were peeled off by adhesion Adhesive wear isoften occurred at the onset of fretting when friction pairscome into contact followed by plastic shearing that plucksoff the ends of the softer asperities is phenomenon is also

(a)

(b)

(c)

Figure 5 Surface topographies of worn scars for (a) 40 microm (left) and 100 microm (right) after 90minutes of fretting test (b) correspondingpreprocessed input area and (c) selected worn area to calculate the wear volume

Advances in Materials Science and Engineering 7

150

125

100W

ear v

olum

e los

s (lowast

106 micro

m3 )

75

50

25

0040

Displacement amplitude (microm)100

Aer 10 minutesAer 30 minutesAer 90 minutes

(a)

24

21

18

15

12

9

6

3

0

Wor

n sc

ar ar

ea (lowast

104 micro

m2 )

Displacement amplitude (microm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(b)

900

750

600

450

300

150

0

Wea

r rat

e (μm

3 mm

)

Displacement amplitude (μm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(c)

Figure 6 Calculated wear volumes (a) worn scar areas (b) and wear rates (c) after dierent time of fretting

00

02

04

06

08

10

12

0 600 1200 1800 2400 3000Time (s)

Coeffi

cien

t of f

rictio

n

3600 4200 4800 5400

40 microm100 microm

Figure 7 Coeordfcient of friction for contact pairs as a function of time

8 Advances in Materials Science and Engineering

attributed to galling and scuordfng [13] Figure 11(b) shows themagnied image in Figure 11(a) that the crack propagationswere prevented by particle detachment and started to spall

eventually becoming loose wear debris Fretted surfaces wererough owing to the plastic deformation and ploughing ef-fects and in some cases surface roughening would provide

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(a)

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(b)

Figure 9 Evolution of fretting loops for 40 microm and 100 microm after (a) 5 and (b) 90minutes of fretting

125100075050025000

ndash025ndash050ndash075ndash100ndash125

60001 60002 60003Time (s)

Coef

ficie

nt o

f fric

tion

60004 60005

40microm

(a)

Time (s)

125100075050025000

ndash025ndash050ndash075ndash100ndash125

Coef

ficie

nt o

f fric

tion

100microm

60001 60002 60003 60004 60005

(b)

Figure 8 Sinusoidal coeordfcient of frictions during 600 s fretting time for (a) 40 microm and (b) 100 microm

Advances in Materials Science and Engineering 9

escape channels for wear debris As the fretting test con-tinued the contact interfaces were slowly accommodated bythe plastic flow and further loading promoted the growth ofsubsurface cracks that parallel to the surface When thesecracks finally extended out to the free surface thin platelet-like wear particles delaminated as shown in Figures 11(c)and 11(d) In the same time when the delamination wasoccurring mostly in the contact center plastic flow of thecontacting surfaces in the periphery and third-body flowclose to the contact border were observed in Figures 11(e)and 11(f) respectively Moreover as temperature increasesbecause of frictional heating during GSR oxidation of thewear particles becomes more ubiquitous and as a

consequence thicker more continuous oxide layer will begenerated e greater contact temperature at this conditionalso causes plastic flow of the oxide film leading to moresevere oxidational wear [19]

Figure 12 shows the SEM images of wear scars andcorresponding 3D surface topographies of the steel ballsoscillated at 40 microm and 100 microm after 90minutes of frettingBoth wear scars were in a circular shape e worn surfacearea which was oscillated at 40 microm also contains the stickdomain in the contact center and slip domain at the pe-riphery as shown in Figure 12(a) However it is clear fromthe picture that a bulk of oxidized X-750 alloy surface layerin black was adhered to the half annulus of the contact which

Slip region

Stick region

Micropitboundary

Slip region

Adhesive microslip

(a)

Stick region

Microcracks

Slip region

Adhesive layerremoval

Crack delamination

(b)

Stick region

Cracks

Slip region

New crack growth alongthe contact border

(c)

Figure 10 SEMmicrographs of Inconel X-750 wear scars during PSR (a) after 10minutes (b) after 30minutes and (c) after 90minutes offretting Displacement amplitude is 40 microm Double arrows represent fretting direction

10 Advances in Materials Science and Engineering

was believed to be plucked off by harder GCr15 ball surfaceduring fretting induced by fatigue According to the wearscar in Figure 12(b) GSR was dominant at 100 microm with thesign of abrasion and small amount of transferred materialson the worn surface Figure 13 shows the EDX spectruminformation for the marked spots in Figure 12 on the wearscar areas Oxide content was very low (146 wt) in thestick region due to the constriction of the relative motionwhile microslip region was reacting with the oxygen in asmall amount On the other hand the highly concentratedoxygen content (29 wt) was detected on the transferredflat material in Figure 13(c) However the oxidation process

on the worn steel surface was faster during GSR rather thanPSR (Figure 13(d))

4 Discussion

e fretting wear process in an ambient temperature is oftendetermined by the contact geometry the oxidation processand the subsequent third-body behavior in the contact in-terface which significantly affect the friction and wearproperties in dry air [11 16 27] Wear properties such asvolume scar area and depth were considerably lowerduring PSR than GSR as shown in Figures 3ndash6 because of

(b)

Adhesive shear

Plowing

(a)

Crack spalling

(b)

Delamination

(c)

Delamination

Oxide layers

(d)

Plastic flow

(e)

Oxidized third-body flow

(f )

Figure 11 SEMmicrographs of Inconel X-750 wear scars during GSR (a) mixed abrasive and adhesive wear at the onset of fretting process(b) spalling of cracks (c d) delamination (e) plastic flow and (f) third-body flow near contact border Displacement amplitude is 100 micromDouble arrows represent fretting direction

Advances in Materials Science and Engineering 11

the small imposed contact area compared to the scale of thenormal load applied Yet the wear rate was maximum in therunning-in period for both cases decreasing gradually withfretting time in Figure 6(c) typically due to the formation ofthe oxide layer (also ldquoglazerdquo layer) on the worn surface which

can enhance the load-carrying capacity avoiding furtherwear [28] During the partial and gross slip conditions thefriction is the outcome of the direct interlocking of thesurface asperities and the trapped oxide debris behavior inthe contact interface respectively In Figure 7 the COF

Highly oxidized Inconel X-750alloy wear layer transfer

a b c

(a)

d

Oxidization

(b)

Figure 12 SEM morphologies of GCr15 steel ball worn scars oscillating at (a) 40 microm and (b) 100 microm Fretting time is 90minutes Doublearrows represent fretting direction

C

O

Fe

Ni SiPt CrMn

Fe

Ni

O KCr KFe KNi K

Element0653wt

019687490056

1888at

017572460044

00

06

12

17

23

29

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(a)

CO

Fe

NiSiPt Cr Mn

Fe

Ni

O KCr KFe KNi K

Element0146wt

026391270104

0470at

026184190091

200 300 400 500 600 700 800 900 10100Energy (keV)

00

05

10

16

21

26

KCnt

(b)

O KCr KFe KNi K

Element2959wt

107305115105

5793at

064702732863

C

O

FeNi SiPt

Cr

Mn Fe

Ni

00

06

12

18

24

30

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(c)

O KCr KFe KNi K

Element1499wt

020378570071

3572at

014953640046

C

O

FeNi

SiPt CrMn

Fe

Ni

200 300 400 500 600 700 800 900 10100Energy (keV)

00

04

09

13

18

22

KCnt

(d)

Figure 13 EDX spectroscopy analysis for worn surfaces at marked spots in Figure 12

12 Advances in Materials Science and Engineering

during PSR was always lower with no apparent fluctuationduring the steady-stage level due to the minimum tangentialforce between the contact interfaces where the central zoneswere mechanically interlocked In this case the highernormal load triggers the traction coefficient where thecritical total sliding shear force is always higher than thetangential force [5 11] However in GSR the highest peak offriction occurred prior to the fluctuating steady-stage levelmainly due to the strong plastic deformation of work-hardened layer of the contacting surfaces [23 29] On theother hand the fluctuations in COF are attributed to themodifications in the contact interface which are linked to thethird-body rheology ie wear debris formation and itsentrapment and ejection from the contact zone [27]

e fretting loops generated by Ft-D curves in Figure 9are good indicators to show the slip condition at any mo-ment e area enclosed by the curves is the measure ofdissipated energy produced by friction [10 30] e frictionwork performed provides a more representative explanationof the surface damage Usually it has been noticed that thewear volume V is proportional to the energy dissipated Edin the contact and described as V αtimes 1113936Ed where α is thefriction energy wear coefficient [6] e degree of slope Sccan be considered as wear characteristics of the slidingconditions and materials Besides the unified slip indexapproach also offers the knowledge of fretting conditionsand considered as an appropriate means for estimatingfretting wear problems In accordance with the terms of slipindex when the slip ratio s⟶ 0 the contacts are in stickand as the slip ratio approaches to 1 partial slip and thengross slip prevail [2] e partial slip contacts in smalldisplacements induce cyclic stresses which favor cracknucleation and propagation but the loading condition isnondissipative with limited surface damage at the peripheryas shown in Figure 10 However the friction dissipation inGSR correlated with the plastic flow delamination andoxidation wear mechanisms causes a large amount ofsurface damage by extending the contact area and reducingthe contact pressure profile (Figure 11)

e main damage mechanisms ie cracking (frettinginduced by fatigue) and material loss (fretting induced bywear) are often appear as a competing process which wasextensively explored during the last decade [1 3 5 6 31ndash34]For instance the material loss during GSR can eliminatesmall cracks or fill up the opening of a deep crack andaccommodate the main portion of the imposed displace-ment as a consequence it strongly reduces the slip am-plitude and then the debris formation In fact the debrisejection has great impact on the third-body establishment ifit is trapped between the contacts the degradation processcan be suppressed and the most of the velocity differencebetween the friction pairs would be completely accommo-dated in a dissipative manner by the powder bed [33 34] Asfor cracking the effects of frictional force and the contactload are huge on the crack initiation and growth duringfretting fatigue where the frictional force triggers the crackinitiation while the contact load disrupts the crack growthduring the propagation period [37] Meanwhile it is re-ported that the cracks on the worn scar surface nucleated

and propagated along the direction of 30ndash50deg to the surfaceinterior which was in the range of calculated maximumshear stress angle [18]

SEM morphology in Figure 12(a) shows the interestingwear phenomenon where the thick layer of Inconel X-750alloy was stuck to the worn surface of the oscillating ball dueto the adhesive microslip In return with the further frettingthe material transferred to the surface of GCr14 ball has thehighest possibility to transfer back to the previous wornsurface of Inconel X-750 alloy [8] Besides the transferredwear layer was highly oxidized compared to the stick and slipregions of the steel ball as shown in Figure 13 e debrisdetached from the contact pairs is essentially composed ofnonmagnetic single component oxides eg Fe2O3 NiO andCr2O3 or more complex oxides eg NiCr2O4 and NiFe2O4[38] However the oxidization process was rapid on theworn surface of the steel ball during GSR which is because ofmore mechanical energy being converted to the thermalheat and it is believed that the frictional heat during GSRwas higher than in PSR [19]

5 Conclusion

e main purpose of this study was to explore the degra-dation evolutions of Inconel X-750 co-acted with GCr15steel ball through the dry fretting tests and observationsanalyses by using 3D surface profiler SEM and EDXAccording to the results the conclusions can be drawn asfollows

(i) e degradation mechanisms of Inconel X-750 weretotally dependent on the fretting regimes and variedwith the fretting time

(ii) e wear volume and wear depth were very low inPSR and wear mechanisms were associated with thedeformations adhesion and fatigue crack emicrocracks were present around the stick domainin 3times104 cycle and the radial cracks fully coveredthe contact center above 105 cycle along with thebigger crack in the contact border e large layer ofductile X-750 alloy was transferred to the wearsurface of the steel ball due to the exhaustion byhighly concentrated cyclic loading during the laterstages of fretting

(iii) In GSR the degradation mechanisms were as fol-lows (1) adhesive wear (galling and scuffing) (2)abrasive wear by third-body particle which is amechanical removal process (3) delaminationwhich is influenced by the material fatigue in theshallow subsurface layer and (4) oxidation of debrisparticles and surface layer due to the higher fric-tional heat which can enhance the load-carryingcapacity as well as reduce the wear rate in the laterstages of fretting process

(iv) e dependence of fretting time was negligibleduring PSR in respect of wear properties such aswear volume scar area and depth However it has agreat impact to evolve the degradation mechanisms

Advances in Materials Science and Engineering 13

from asperity deformation to the crack initiationand propagation which is a critical damage duringPSR On the other hand the wear volume and scararea were increased significantly by time duringGSR but the degradation evolutions were combinedand repeated with the mentioned wear mechanismsin a whole fretting process

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

e first author would like to acknowledge the scholarshipsupport from China Scholarship Council (CSC) is workwas supported by the Aeronautical Science Fund of China(Grant no 20164058002) National Natural Science Foun-dation of China (Grant No51735006) and Tsinghua Uni-versity Initiative Scientific Research Program

References

[1] R B Waterhouse ldquoFretting wearrdquo Wear vol 100 no 1ndash3pp 107ndash118 1984

[2] M Varenberg I Etsion and G Halperin ldquoSlip index a newunified approach to frettingrdquo Tribology Letters vol 17 no 3pp 569ndash573 2004

[3] O Vingsbo and S Soderberg ldquoOn fretting mapsrdquo Wearvol 126 no 2 pp 131ndash147 1988

[4] R D Mindlin and H Deresiewiez ldquoElastic spheres in contactunder varying oblique forcesrdquo Journal of Applied Mechanicsvol 20 pp 327ndash344 1953

[5] Z R Zhou and L Vincent ldquoMixed fretting regimerdquo Wearvol 181ndash183 pp 531ndash536 1995

[6] S Fouvry P Kapsa and L Vincent ldquoQuantification offretting damagerdquo Wear vol 200 no 1-2 pp 186ndash205 1996

[7] J Yu L Qian B Yu and Z Zhou ldquoNanofretting behavior ofmonocrystalline silicon (100) against SiO2 microsphere invacuumrdquo Tribology Letters vol 34 no 1 pp 31ndash40 2009

[8] H Mohrbacher J P Celis and J R Roos ldquoLaboratory testingof displacement and load induced frettingrdquo Tribology In-ternational vol 28 no 5 pp 269ndash278 1995

[9] Z R Zhou S Fayeulle and L Vincent ldquoCracking behaviourof various aluminium alloys during fretting wearrdquo Wearvol 155 no 2 pp 317ndash330 1992

[10] S Fouvry P Kapsa H Zahouani and L Vincent ldquoWearanalysis in fretting of hard coatings through a dissipatedenergy conceptrdquo Wear vol 203-204 pp 393ndash403 1997

[11] J Li and Y H Lu ldquoEffects of displacement amplitude onfretting wear behaviors and mechanism of Inconel 600 alloyrdquoWear vol 304 no 1-2 pp 223ndash230 2013

[12] G B Stachowiak and G W Stachowiak ldquoFretting wear andfriction behaviour of engineering ceramicsrdquo Wear vol 190no 2 pp 212ndash218 1995

[13] B Bhushan and B K Gupta Handbook of Tribology Mate-rials Coatings and Surface Treatments McGraw-Hill NewYork NY USA 1991

[14] H Y Zhang Y H Lu M Ma and J Li ldquoEffect of precipitatedcarbides on the fretting wear behavior of Inconel 600 alloyrdquoWear vol 315 no 1-2 pp 58ndash67 2014

[15] X Mi W X Wang X M Xiong et al ldquoInvestigation offretting wear behavior of Inconel 690 alloy in tubeplatecontact configurationrdquoWear vol 328-329 pp 582ndash590 2015

[16] L Jie L Yonghao Z Haoyang and L Xin ldquoEffect of grain sizeand hardness on fretting wear behavior of inconel 600 alloysrdquoTribology International vol 81 pp 215ndash222 2015

[17] L Xin B B Yang Z H Wang J Li Y H Lu and T ShojildquoMicrostructural evolution of subsurface on inconel 690TTalloy subjected to fretting wear at elevated temperaturerdquoMaterials amp Design vol 104 pp 152ndash161 2016

[18] J Li B B Yang Y H Lu L Xin Z H Wang and T Shojildquoe degradation mechanism of inconel 690TT induced byfretting wear in airrdquo Tribology International vol 116pp 147ndash154 2017

[19] G Xianglong L Ping T Lichen et al ldquoEffects of slidingamplitude and normal load on the fretting wear behavior ofalloy 690 tube exposed to high temperature waterrdquo TribologyInternational vol 116 pp 155ndash163 2017

[20] Special Metals INCONEL alloy X-750 Data Sheet 2004Publication No SMC-067 httpwwwspecialmetalscom

[21] C Marsh S Depinoy and D Kaoumi ldquoEffect of heattreatment on the temperature dependence of the fracturebehavior of X-750 alloyrdquo Materials Science and EngineeringA vol 677 pp 474ndash484 2016

[22] D Wenbo S Yanhua D Chunhua and Y Lie ldquoStructuralstiffness of X-750 alloy bump foil strips for compliant foilbearings with different heat treatmentsrdquo Journal of Tribologyvol 138 no 3 article 031702 2016

[23] G X Chen and Z R Zhou ldquoStudy on transition betweenfretting and reciprocating sliding wearrdquo Wear vol 250no 1ndash12 pp 665ndash672 2001

[24] J F Archard ldquoContact and rubbing of flat surfacesrdquo Journal ofApplied Physics vol 24 no 8 pp 981ndash988 1953

[25] S C Lim M F Ashby and J H Brunton ldquoWear-ratetransitions and their relationship to wear mechanismsrdquoActa Metallurgica vol 35 no 6 pp 1343ndash1348 1987

[26] S C Lim ldquoRecent developments in wear-mechanism mapsrdquoTribology International vol 31 no 1ndash3 pp 87ndash97 1998

[27] X LongW Zihao L Jie Y Lu and T Shoji ldquoMicrostructuralcharacterization of subsurface caused by fretting wear ofinconel 690TT alloyrdquo Material Characteristics vol 115pp 32ndash38 2016

[28] R Rybiak S Fouvry and B Bonnet ldquoFretting wear of stainlesssteels under variable temperature conditions introduction ofa ldquocompositerdquo wear lawrdquoWear vol 268 no 3-4 pp 413ndash4232010

[29] J F Zheng J Luo J L Mo J F Peng X S Jin andMH ZhuldquoFretting wear behaviors of a railway axle steelrdquo TribologyInternational vol 43 no 5-6 pp 906ndash911 2010

[30] K V Virendra N Hamza S S R Ganesh H MurthyA N Majila and D C Fernando ldquoEffect of contact pressureand stress ratio on the fretting fatigue behaviour of Ti-6Al-4Vrdquo Material Science and Engineering A vol 707 pp 647ndash656 2017

[31] J J Madge S B Leen and P H Shipway ldquoe critical role offretting wear in the analysis of fretting fatiguerdquoWear vol 263no 1ndash6 pp 542ndash551 2007

14 Advances in Materials Science and Engineering

third-body flow between contact surfaces Red-brown oxi-dized powders were ejected from contact surfaces during thefretting process which can serve as abrasive particles prior totheir expulsion For example Figure 11(a) shows the wearmode onset of the fretting process in the contact centerwhere plowing grooves parallel to the sliding direction was

formed due to the larger relative motion by abrasive par-ticles followed by plastic shearing so that thick layers ofX-750 alloy were peeled off by adhesion Adhesive wear isoften occurred at the onset of fretting when friction pairscome into contact followed by plastic shearing that plucksoff the ends of the softer asperities is phenomenon is also

(a)

(b)

(c)

Figure 5 Surface topographies of worn scars for (a) 40 microm (left) and 100 microm (right) after 90minutes of fretting test (b) correspondingpreprocessed input area and (c) selected worn area to calculate the wear volume

Advances in Materials Science and Engineering 7

150

125

100W

ear v

olum

e los

s (lowast

106 micro

m3 )

75

50

25

0040

Displacement amplitude (microm)100

Aer 10 minutesAer 30 minutesAer 90 minutes

(a)

24

21

18

15

12

9

6

3

0

Wor

n sc

ar ar

ea (lowast

104 micro

m2 )

Displacement amplitude (microm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(b)

900

750

600

450

300

150

0

Wea

r rat

e (μm

3 mm

)

Displacement amplitude (μm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(c)

Figure 6 Calculated wear volumes (a) worn scar areas (b) and wear rates (c) after dierent time of fretting

00

02

04

06

08

10

12

0 600 1200 1800 2400 3000Time (s)

Coeffi

cien

t of f

rictio

n

3600 4200 4800 5400

40 microm100 microm

Figure 7 Coeordfcient of friction for contact pairs as a function of time

8 Advances in Materials Science and Engineering

attributed to galling and scuordfng [13] Figure 11(b) shows themagnied image in Figure 11(a) that the crack propagationswere prevented by particle detachment and started to spall

eventually becoming loose wear debris Fretted surfaces wererough owing to the plastic deformation and ploughing ef-fects and in some cases surface roughening would provide

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(a)

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(b)

Figure 9 Evolution of fretting loops for 40 microm and 100 microm after (a) 5 and (b) 90minutes of fretting

125100075050025000

ndash025ndash050ndash075ndash100ndash125

60001 60002 60003Time (s)

Coef

ficie

nt o

f fric

tion

60004 60005

40microm

(a)

Time (s)

125100075050025000

ndash025ndash050ndash075ndash100ndash125

Coef

ficie

nt o

f fric

tion

100microm

60001 60002 60003 60004 60005

(b)

Figure 8 Sinusoidal coeordfcient of frictions during 600 s fretting time for (a) 40 microm and (b) 100 microm

Advances in Materials Science and Engineering 9

escape channels for wear debris As the fretting test con-tinued the contact interfaces were slowly accommodated bythe plastic flow and further loading promoted the growth ofsubsurface cracks that parallel to the surface When thesecracks finally extended out to the free surface thin platelet-like wear particles delaminated as shown in Figures 11(c)and 11(d) In the same time when the delamination wasoccurring mostly in the contact center plastic flow of thecontacting surfaces in the periphery and third-body flowclose to the contact border were observed in Figures 11(e)and 11(f) respectively Moreover as temperature increasesbecause of frictional heating during GSR oxidation of thewear particles becomes more ubiquitous and as a

consequence thicker more continuous oxide layer will begenerated e greater contact temperature at this conditionalso causes plastic flow of the oxide film leading to moresevere oxidational wear [19]

Figure 12 shows the SEM images of wear scars andcorresponding 3D surface topographies of the steel ballsoscillated at 40 microm and 100 microm after 90minutes of frettingBoth wear scars were in a circular shape e worn surfacearea which was oscillated at 40 microm also contains the stickdomain in the contact center and slip domain at the pe-riphery as shown in Figure 12(a) However it is clear fromthe picture that a bulk of oxidized X-750 alloy surface layerin black was adhered to the half annulus of the contact which

Slip region

Stick region

Micropitboundary

Slip region

Adhesive microslip

(a)

Stick region

Microcracks

Slip region

Adhesive layerremoval

Crack delamination

(b)

Stick region

Cracks

Slip region

New crack growth alongthe contact border

(c)

Figure 10 SEMmicrographs of Inconel X-750 wear scars during PSR (a) after 10minutes (b) after 30minutes and (c) after 90minutes offretting Displacement amplitude is 40 microm Double arrows represent fretting direction

10 Advances in Materials Science and Engineering

was believed to be plucked off by harder GCr15 ball surfaceduring fretting induced by fatigue According to the wearscar in Figure 12(b) GSR was dominant at 100 microm with thesign of abrasion and small amount of transferred materialson the worn surface Figure 13 shows the EDX spectruminformation for the marked spots in Figure 12 on the wearscar areas Oxide content was very low (146 wt) in thestick region due to the constriction of the relative motionwhile microslip region was reacting with the oxygen in asmall amount On the other hand the highly concentratedoxygen content (29 wt) was detected on the transferredflat material in Figure 13(c) However the oxidation process

on the worn steel surface was faster during GSR rather thanPSR (Figure 13(d))

4 Discussion

e fretting wear process in an ambient temperature is oftendetermined by the contact geometry the oxidation processand the subsequent third-body behavior in the contact in-terface which significantly affect the friction and wearproperties in dry air [11 16 27] Wear properties such asvolume scar area and depth were considerably lowerduring PSR than GSR as shown in Figures 3ndash6 because of

(b)

Adhesive shear

Plowing

(a)

Crack spalling

(b)

Delamination

(c)

Delamination

Oxide layers

(d)

Plastic flow

(e)

Oxidized third-body flow

(f )

Figure 11 SEMmicrographs of Inconel X-750 wear scars during GSR (a) mixed abrasive and adhesive wear at the onset of fretting process(b) spalling of cracks (c d) delamination (e) plastic flow and (f) third-body flow near contact border Displacement amplitude is 100 micromDouble arrows represent fretting direction

Advances in Materials Science and Engineering 11

the small imposed contact area compared to the scale of thenormal load applied Yet the wear rate was maximum in therunning-in period for both cases decreasing gradually withfretting time in Figure 6(c) typically due to the formation ofthe oxide layer (also ldquoglazerdquo layer) on the worn surface which

can enhance the load-carrying capacity avoiding furtherwear [28] During the partial and gross slip conditions thefriction is the outcome of the direct interlocking of thesurface asperities and the trapped oxide debris behavior inthe contact interface respectively In Figure 7 the COF

Highly oxidized Inconel X-750alloy wear layer transfer

a b c

(a)

d

Oxidization

(b)

Figure 12 SEM morphologies of GCr15 steel ball worn scars oscillating at (a) 40 microm and (b) 100 microm Fretting time is 90minutes Doublearrows represent fretting direction

C

O

Fe

Ni SiPt CrMn

Fe

Ni

O KCr KFe KNi K

Element0653wt

019687490056

1888at

017572460044

00

06

12

17

23

29

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(a)

CO

Fe

NiSiPt Cr Mn

Fe

Ni

O KCr KFe KNi K

Element0146wt

026391270104

0470at

026184190091

200 300 400 500 600 700 800 900 10100Energy (keV)

00

05

10

16

21

26

KCnt

(b)

O KCr KFe KNi K

Element2959wt

107305115105

5793at

064702732863

C

O

FeNi SiPt

Cr

Mn Fe

Ni

00

06

12

18

24

30

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(c)

O KCr KFe KNi K

Element1499wt

020378570071

3572at

014953640046

C

O

FeNi

SiPt CrMn

Fe

Ni

200 300 400 500 600 700 800 900 10100Energy (keV)

00

04

09

13

18

22

KCnt

(d)

Figure 13 EDX spectroscopy analysis for worn surfaces at marked spots in Figure 12

12 Advances in Materials Science and Engineering

during PSR was always lower with no apparent fluctuationduring the steady-stage level due to the minimum tangentialforce between the contact interfaces where the central zoneswere mechanically interlocked In this case the highernormal load triggers the traction coefficient where thecritical total sliding shear force is always higher than thetangential force [5 11] However in GSR the highest peak offriction occurred prior to the fluctuating steady-stage levelmainly due to the strong plastic deformation of work-hardened layer of the contacting surfaces [23 29] On theother hand the fluctuations in COF are attributed to themodifications in the contact interface which are linked to thethird-body rheology ie wear debris formation and itsentrapment and ejection from the contact zone [27]

e fretting loops generated by Ft-D curves in Figure 9are good indicators to show the slip condition at any mo-ment e area enclosed by the curves is the measure ofdissipated energy produced by friction [10 30] e frictionwork performed provides a more representative explanationof the surface damage Usually it has been noticed that thewear volume V is proportional to the energy dissipated Edin the contact and described as V αtimes 1113936Ed where α is thefriction energy wear coefficient [6] e degree of slope Sccan be considered as wear characteristics of the slidingconditions and materials Besides the unified slip indexapproach also offers the knowledge of fretting conditionsand considered as an appropriate means for estimatingfretting wear problems In accordance with the terms of slipindex when the slip ratio s⟶ 0 the contacts are in stickand as the slip ratio approaches to 1 partial slip and thengross slip prevail [2] e partial slip contacts in smalldisplacements induce cyclic stresses which favor cracknucleation and propagation but the loading condition isnondissipative with limited surface damage at the peripheryas shown in Figure 10 However the friction dissipation inGSR correlated with the plastic flow delamination andoxidation wear mechanisms causes a large amount ofsurface damage by extending the contact area and reducingthe contact pressure profile (Figure 11)

e main damage mechanisms ie cracking (frettinginduced by fatigue) and material loss (fretting induced bywear) are often appear as a competing process which wasextensively explored during the last decade [1 3 5 6 31ndash34]For instance the material loss during GSR can eliminatesmall cracks or fill up the opening of a deep crack andaccommodate the main portion of the imposed displace-ment as a consequence it strongly reduces the slip am-plitude and then the debris formation In fact the debrisejection has great impact on the third-body establishment ifit is trapped between the contacts the degradation processcan be suppressed and the most of the velocity differencebetween the friction pairs would be completely accommo-dated in a dissipative manner by the powder bed [33 34] Asfor cracking the effects of frictional force and the contactload are huge on the crack initiation and growth duringfretting fatigue where the frictional force triggers the crackinitiation while the contact load disrupts the crack growthduring the propagation period [37] Meanwhile it is re-ported that the cracks on the worn scar surface nucleated

and propagated along the direction of 30ndash50deg to the surfaceinterior which was in the range of calculated maximumshear stress angle [18]

SEM morphology in Figure 12(a) shows the interestingwear phenomenon where the thick layer of Inconel X-750alloy was stuck to the worn surface of the oscillating ball dueto the adhesive microslip In return with the further frettingthe material transferred to the surface of GCr14 ball has thehighest possibility to transfer back to the previous wornsurface of Inconel X-750 alloy [8] Besides the transferredwear layer was highly oxidized compared to the stick and slipregions of the steel ball as shown in Figure 13 e debrisdetached from the contact pairs is essentially composed ofnonmagnetic single component oxides eg Fe2O3 NiO andCr2O3 or more complex oxides eg NiCr2O4 and NiFe2O4[38] However the oxidization process was rapid on theworn surface of the steel ball during GSR which is because ofmore mechanical energy being converted to the thermalheat and it is believed that the frictional heat during GSRwas higher than in PSR [19]

5 Conclusion

e main purpose of this study was to explore the degra-dation evolutions of Inconel X-750 co-acted with GCr15steel ball through the dry fretting tests and observationsanalyses by using 3D surface profiler SEM and EDXAccording to the results the conclusions can be drawn asfollows

(i) e degradation mechanisms of Inconel X-750 weretotally dependent on the fretting regimes and variedwith the fretting time

(ii) e wear volume and wear depth were very low inPSR and wear mechanisms were associated with thedeformations adhesion and fatigue crack emicrocracks were present around the stick domainin 3times104 cycle and the radial cracks fully coveredthe contact center above 105 cycle along with thebigger crack in the contact border e large layer ofductile X-750 alloy was transferred to the wearsurface of the steel ball due to the exhaustion byhighly concentrated cyclic loading during the laterstages of fretting

(iii) In GSR the degradation mechanisms were as fol-lows (1) adhesive wear (galling and scuffing) (2)abrasive wear by third-body particle which is amechanical removal process (3) delaminationwhich is influenced by the material fatigue in theshallow subsurface layer and (4) oxidation of debrisparticles and surface layer due to the higher fric-tional heat which can enhance the load-carryingcapacity as well as reduce the wear rate in the laterstages of fretting process

(iv) e dependence of fretting time was negligibleduring PSR in respect of wear properties such aswear volume scar area and depth However it has agreat impact to evolve the degradation mechanisms

Advances in Materials Science and Engineering 13

from asperity deformation to the crack initiationand propagation which is a critical damage duringPSR On the other hand the wear volume and scararea were increased significantly by time duringGSR but the degradation evolutions were combinedand repeated with the mentioned wear mechanismsin a whole fretting process

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

e first author would like to acknowledge the scholarshipsupport from China Scholarship Council (CSC) is workwas supported by the Aeronautical Science Fund of China(Grant no 20164058002) National Natural Science Foun-dation of China (Grant No51735006) and Tsinghua Uni-versity Initiative Scientific Research Program

References

[1] R B Waterhouse ldquoFretting wearrdquo Wear vol 100 no 1ndash3pp 107ndash118 1984

[2] M Varenberg I Etsion and G Halperin ldquoSlip index a newunified approach to frettingrdquo Tribology Letters vol 17 no 3pp 569ndash573 2004

[3] O Vingsbo and S Soderberg ldquoOn fretting mapsrdquo Wearvol 126 no 2 pp 131ndash147 1988

[4] R D Mindlin and H Deresiewiez ldquoElastic spheres in contactunder varying oblique forcesrdquo Journal of Applied Mechanicsvol 20 pp 327ndash344 1953

[5] Z R Zhou and L Vincent ldquoMixed fretting regimerdquo Wearvol 181ndash183 pp 531ndash536 1995

[6] S Fouvry P Kapsa and L Vincent ldquoQuantification offretting damagerdquo Wear vol 200 no 1-2 pp 186ndash205 1996

[7] J Yu L Qian B Yu and Z Zhou ldquoNanofretting behavior ofmonocrystalline silicon (100) against SiO2 microsphere invacuumrdquo Tribology Letters vol 34 no 1 pp 31ndash40 2009

[8] H Mohrbacher J P Celis and J R Roos ldquoLaboratory testingof displacement and load induced frettingrdquo Tribology In-ternational vol 28 no 5 pp 269ndash278 1995

[9] Z R Zhou S Fayeulle and L Vincent ldquoCracking behaviourof various aluminium alloys during fretting wearrdquo Wearvol 155 no 2 pp 317ndash330 1992

[10] S Fouvry P Kapsa H Zahouani and L Vincent ldquoWearanalysis in fretting of hard coatings through a dissipatedenergy conceptrdquo Wear vol 203-204 pp 393ndash403 1997

[11] J Li and Y H Lu ldquoEffects of displacement amplitude onfretting wear behaviors and mechanism of Inconel 600 alloyrdquoWear vol 304 no 1-2 pp 223ndash230 2013

[12] G B Stachowiak and G W Stachowiak ldquoFretting wear andfriction behaviour of engineering ceramicsrdquo Wear vol 190no 2 pp 212ndash218 1995

[13] B Bhushan and B K Gupta Handbook of Tribology Mate-rials Coatings and Surface Treatments McGraw-Hill NewYork NY USA 1991

[14] H Y Zhang Y H Lu M Ma and J Li ldquoEffect of precipitatedcarbides on the fretting wear behavior of Inconel 600 alloyrdquoWear vol 315 no 1-2 pp 58ndash67 2014

[15] X Mi W X Wang X M Xiong et al ldquoInvestigation offretting wear behavior of Inconel 690 alloy in tubeplatecontact configurationrdquoWear vol 328-329 pp 582ndash590 2015

[16] L Jie L Yonghao Z Haoyang and L Xin ldquoEffect of grain sizeand hardness on fretting wear behavior of inconel 600 alloysrdquoTribology International vol 81 pp 215ndash222 2015

[17] L Xin B B Yang Z H Wang J Li Y H Lu and T ShojildquoMicrostructural evolution of subsurface on inconel 690TTalloy subjected to fretting wear at elevated temperaturerdquoMaterials amp Design vol 104 pp 152ndash161 2016

[18] J Li B B Yang Y H Lu L Xin Z H Wang and T Shojildquoe degradation mechanism of inconel 690TT induced byfretting wear in airrdquo Tribology International vol 116pp 147ndash154 2017

[19] G Xianglong L Ping T Lichen et al ldquoEffects of slidingamplitude and normal load on the fretting wear behavior ofalloy 690 tube exposed to high temperature waterrdquo TribologyInternational vol 116 pp 155ndash163 2017

[20] Special Metals INCONEL alloy X-750 Data Sheet 2004Publication No SMC-067 httpwwwspecialmetalscom

[21] C Marsh S Depinoy and D Kaoumi ldquoEffect of heattreatment on the temperature dependence of the fracturebehavior of X-750 alloyrdquo Materials Science and EngineeringA vol 677 pp 474ndash484 2016

[22] D Wenbo S Yanhua D Chunhua and Y Lie ldquoStructuralstiffness of X-750 alloy bump foil strips for compliant foilbearings with different heat treatmentsrdquo Journal of Tribologyvol 138 no 3 article 031702 2016

[23] G X Chen and Z R Zhou ldquoStudy on transition betweenfretting and reciprocating sliding wearrdquo Wear vol 250no 1ndash12 pp 665ndash672 2001

[24] J F Archard ldquoContact and rubbing of flat surfacesrdquo Journal ofApplied Physics vol 24 no 8 pp 981ndash988 1953

[25] S C Lim M F Ashby and J H Brunton ldquoWear-ratetransitions and their relationship to wear mechanismsrdquoActa Metallurgica vol 35 no 6 pp 1343ndash1348 1987

[26] S C Lim ldquoRecent developments in wear-mechanism mapsrdquoTribology International vol 31 no 1ndash3 pp 87ndash97 1998

[27] X LongW Zihao L Jie Y Lu and T Shoji ldquoMicrostructuralcharacterization of subsurface caused by fretting wear ofinconel 690TT alloyrdquo Material Characteristics vol 115pp 32ndash38 2016

[28] R Rybiak S Fouvry and B Bonnet ldquoFretting wear of stainlesssteels under variable temperature conditions introduction ofa ldquocompositerdquo wear lawrdquoWear vol 268 no 3-4 pp 413ndash4232010

[29] J F Zheng J Luo J L Mo J F Peng X S Jin andMH ZhuldquoFretting wear behaviors of a railway axle steelrdquo TribologyInternational vol 43 no 5-6 pp 906ndash911 2010

[30] K V Virendra N Hamza S S R Ganesh H MurthyA N Majila and D C Fernando ldquoEffect of contact pressureand stress ratio on the fretting fatigue behaviour of Ti-6Al-4Vrdquo Material Science and Engineering A vol 707 pp 647ndash656 2017

[31] J J Madge S B Leen and P H Shipway ldquoe critical role offretting wear in the analysis of fretting fatiguerdquoWear vol 263no 1ndash6 pp 542ndash551 2007

14 Advances in Materials Science and Engineering

150

125

100W

ear v

olum

e los

s (lowast

106 micro

m3 )

75

50

25

0040

Displacement amplitude (microm)100

Aer 10 minutesAer 30 minutesAer 90 minutes

(a)

24

21

18

15

12

9

6

3

0

Wor

n sc

ar ar

ea (lowast

104 micro

m2 )

Displacement amplitude (microm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(b)

900

750

600

450

300

150

0

Wea

r rat

e (μm

3 mm

)

Displacement amplitude (μm)40 100

Aer 10 minutesAer 30 minutesAer 90 minutes

(c)

Figure 6 Calculated wear volumes (a) worn scar areas (b) and wear rates (c) after dierent time of fretting

00

02

04

06

08

10

12

0 600 1200 1800 2400 3000Time (s)

Coeffi

cien

t of f

rictio

n

3600 4200 4800 5400

40 microm100 microm

Figure 7 Coeordfcient of friction for contact pairs as a function of time

8 Advances in Materials Science and Engineering

attributed to galling and scuordfng [13] Figure 11(b) shows themagnied image in Figure 11(a) that the crack propagationswere prevented by particle detachment and started to spall

eventually becoming loose wear debris Fretted surfaces wererough owing to the plastic deformation and ploughing ef-fects and in some cases surface roughening would provide

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(a)

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(b)

Figure 9 Evolution of fretting loops for 40 microm and 100 microm after (a) 5 and (b) 90minutes of fretting

125100075050025000

ndash025ndash050ndash075ndash100ndash125

60001 60002 60003Time (s)

Coef

ficie

nt o

f fric

tion

60004 60005

40microm

(a)

Time (s)

125100075050025000

ndash025ndash050ndash075ndash100ndash125

Coef

ficie

nt o

f fric

tion

100microm

60001 60002 60003 60004 60005

(b)

Figure 8 Sinusoidal coeordfcient of frictions during 600 s fretting time for (a) 40 microm and (b) 100 microm

Advances in Materials Science and Engineering 9

escape channels for wear debris As the fretting test con-tinued the contact interfaces were slowly accommodated bythe plastic flow and further loading promoted the growth ofsubsurface cracks that parallel to the surface When thesecracks finally extended out to the free surface thin platelet-like wear particles delaminated as shown in Figures 11(c)and 11(d) In the same time when the delamination wasoccurring mostly in the contact center plastic flow of thecontacting surfaces in the periphery and third-body flowclose to the contact border were observed in Figures 11(e)and 11(f) respectively Moreover as temperature increasesbecause of frictional heating during GSR oxidation of thewear particles becomes more ubiquitous and as a

consequence thicker more continuous oxide layer will begenerated e greater contact temperature at this conditionalso causes plastic flow of the oxide film leading to moresevere oxidational wear [19]

Figure 12 shows the SEM images of wear scars andcorresponding 3D surface topographies of the steel ballsoscillated at 40 microm and 100 microm after 90minutes of frettingBoth wear scars were in a circular shape e worn surfacearea which was oscillated at 40 microm also contains the stickdomain in the contact center and slip domain at the pe-riphery as shown in Figure 12(a) However it is clear fromthe picture that a bulk of oxidized X-750 alloy surface layerin black was adhered to the half annulus of the contact which

Slip region

Stick region

Micropitboundary

Slip region

Adhesive microslip

(a)

Stick region

Microcracks

Slip region

Adhesive layerremoval

Crack delamination

(b)

Stick region

Cracks

Slip region

New crack growth alongthe contact border

(c)

Figure 10 SEMmicrographs of Inconel X-750 wear scars during PSR (a) after 10minutes (b) after 30minutes and (c) after 90minutes offretting Displacement amplitude is 40 microm Double arrows represent fretting direction

10 Advances in Materials Science and Engineering

was believed to be plucked off by harder GCr15 ball surfaceduring fretting induced by fatigue According to the wearscar in Figure 12(b) GSR was dominant at 100 microm with thesign of abrasion and small amount of transferred materialson the worn surface Figure 13 shows the EDX spectruminformation for the marked spots in Figure 12 on the wearscar areas Oxide content was very low (146 wt) in thestick region due to the constriction of the relative motionwhile microslip region was reacting with the oxygen in asmall amount On the other hand the highly concentratedoxygen content (29 wt) was detected on the transferredflat material in Figure 13(c) However the oxidation process

on the worn steel surface was faster during GSR rather thanPSR (Figure 13(d))

4 Discussion

e fretting wear process in an ambient temperature is oftendetermined by the contact geometry the oxidation processand the subsequent third-body behavior in the contact in-terface which significantly affect the friction and wearproperties in dry air [11 16 27] Wear properties such asvolume scar area and depth were considerably lowerduring PSR than GSR as shown in Figures 3ndash6 because of

(b)

Adhesive shear

Plowing

(a)

Crack spalling

(b)

Delamination

(c)

Delamination

Oxide layers

(d)

Plastic flow

(e)

Oxidized third-body flow

(f )

Figure 11 SEMmicrographs of Inconel X-750 wear scars during GSR (a) mixed abrasive and adhesive wear at the onset of fretting process(b) spalling of cracks (c d) delamination (e) plastic flow and (f) third-body flow near contact border Displacement amplitude is 100 micromDouble arrows represent fretting direction

Advances in Materials Science and Engineering 11

the small imposed contact area compared to the scale of thenormal load applied Yet the wear rate was maximum in therunning-in period for both cases decreasing gradually withfretting time in Figure 6(c) typically due to the formation ofthe oxide layer (also ldquoglazerdquo layer) on the worn surface which

can enhance the load-carrying capacity avoiding furtherwear [28] During the partial and gross slip conditions thefriction is the outcome of the direct interlocking of thesurface asperities and the trapped oxide debris behavior inthe contact interface respectively In Figure 7 the COF

Highly oxidized Inconel X-750alloy wear layer transfer

a b c

(a)

d

Oxidization

(b)

Figure 12 SEM morphologies of GCr15 steel ball worn scars oscillating at (a) 40 microm and (b) 100 microm Fretting time is 90minutes Doublearrows represent fretting direction

C

O

Fe

Ni SiPt CrMn

Fe

Ni

O KCr KFe KNi K

Element0653wt

019687490056

1888at

017572460044

00

06

12

17

23

29

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(a)

CO

Fe

NiSiPt Cr Mn

Fe

Ni

O KCr KFe KNi K

Element0146wt

026391270104

0470at

026184190091

200 300 400 500 600 700 800 900 10100Energy (keV)

00

05

10

16

21

26

KCnt

(b)

O KCr KFe KNi K

Element2959wt

107305115105

5793at

064702732863

C

O

FeNi SiPt

Cr

Mn Fe

Ni

00

06

12

18

24

30

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(c)

O KCr KFe KNi K

Element1499wt

020378570071

3572at

014953640046

C

O

FeNi

SiPt CrMn

Fe

Ni

200 300 400 500 600 700 800 900 10100Energy (keV)

00

04

09

13

18

22

KCnt

(d)

Figure 13 EDX spectroscopy analysis for worn surfaces at marked spots in Figure 12

12 Advances in Materials Science and Engineering

during PSR was always lower with no apparent fluctuationduring the steady-stage level due to the minimum tangentialforce between the contact interfaces where the central zoneswere mechanically interlocked In this case the highernormal load triggers the traction coefficient where thecritical total sliding shear force is always higher than thetangential force [5 11] However in GSR the highest peak offriction occurred prior to the fluctuating steady-stage levelmainly due to the strong plastic deformation of work-hardened layer of the contacting surfaces [23 29] On theother hand the fluctuations in COF are attributed to themodifications in the contact interface which are linked to thethird-body rheology ie wear debris formation and itsentrapment and ejection from the contact zone [27]

e fretting loops generated by Ft-D curves in Figure 9are good indicators to show the slip condition at any mo-ment e area enclosed by the curves is the measure ofdissipated energy produced by friction [10 30] e frictionwork performed provides a more representative explanationof the surface damage Usually it has been noticed that thewear volume V is proportional to the energy dissipated Edin the contact and described as V αtimes 1113936Ed where α is thefriction energy wear coefficient [6] e degree of slope Sccan be considered as wear characteristics of the slidingconditions and materials Besides the unified slip indexapproach also offers the knowledge of fretting conditionsand considered as an appropriate means for estimatingfretting wear problems In accordance with the terms of slipindex when the slip ratio s⟶ 0 the contacts are in stickand as the slip ratio approaches to 1 partial slip and thengross slip prevail [2] e partial slip contacts in smalldisplacements induce cyclic stresses which favor cracknucleation and propagation but the loading condition isnondissipative with limited surface damage at the peripheryas shown in Figure 10 However the friction dissipation inGSR correlated with the plastic flow delamination andoxidation wear mechanisms causes a large amount ofsurface damage by extending the contact area and reducingthe contact pressure profile (Figure 11)

e main damage mechanisms ie cracking (frettinginduced by fatigue) and material loss (fretting induced bywear) are often appear as a competing process which wasextensively explored during the last decade [1 3 5 6 31ndash34]For instance the material loss during GSR can eliminatesmall cracks or fill up the opening of a deep crack andaccommodate the main portion of the imposed displace-ment as a consequence it strongly reduces the slip am-plitude and then the debris formation In fact the debrisejection has great impact on the third-body establishment ifit is trapped between the contacts the degradation processcan be suppressed and the most of the velocity differencebetween the friction pairs would be completely accommo-dated in a dissipative manner by the powder bed [33 34] Asfor cracking the effects of frictional force and the contactload are huge on the crack initiation and growth duringfretting fatigue where the frictional force triggers the crackinitiation while the contact load disrupts the crack growthduring the propagation period [37] Meanwhile it is re-ported that the cracks on the worn scar surface nucleated

and propagated along the direction of 30ndash50deg to the surfaceinterior which was in the range of calculated maximumshear stress angle [18]

SEM morphology in Figure 12(a) shows the interestingwear phenomenon where the thick layer of Inconel X-750alloy was stuck to the worn surface of the oscillating ball dueto the adhesive microslip In return with the further frettingthe material transferred to the surface of GCr14 ball has thehighest possibility to transfer back to the previous wornsurface of Inconel X-750 alloy [8] Besides the transferredwear layer was highly oxidized compared to the stick and slipregions of the steel ball as shown in Figure 13 e debrisdetached from the contact pairs is essentially composed ofnonmagnetic single component oxides eg Fe2O3 NiO andCr2O3 or more complex oxides eg NiCr2O4 and NiFe2O4[38] However the oxidization process was rapid on theworn surface of the steel ball during GSR which is because ofmore mechanical energy being converted to the thermalheat and it is believed that the frictional heat during GSRwas higher than in PSR [19]

5 Conclusion

e main purpose of this study was to explore the degra-dation evolutions of Inconel X-750 co-acted with GCr15steel ball through the dry fretting tests and observationsanalyses by using 3D surface profiler SEM and EDXAccording to the results the conclusions can be drawn asfollows

(i) e degradation mechanisms of Inconel X-750 weretotally dependent on the fretting regimes and variedwith the fretting time

(ii) e wear volume and wear depth were very low inPSR and wear mechanisms were associated with thedeformations adhesion and fatigue crack emicrocracks were present around the stick domainin 3times104 cycle and the radial cracks fully coveredthe contact center above 105 cycle along with thebigger crack in the contact border e large layer ofductile X-750 alloy was transferred to the wearsurface of the steel ball due to the exhaustion byhighly concentrated cyclic loading during the laterstages of fretting

(iii) In GSR the degradation mechanisms were as fol-lows (1) adhesive wear (galling and scuffing) (2)abrasive wear by third-body particle which is amechanical removal process (3) delaminationwhich is influenced by the material fatigue in theshallow subsurface layer and (4) oxidation of debrisparticles and surface layer due to the higher fric-tional heat which can enhance the load-carryingcapacity as well as reduce the wear rate in the laterstages of fretting process

(iv) e dependence of fretting time was negligibleduring PSR in respect of wear properties such aswear volume scar area and depth However it has agreat impact to evolve the degradation mechanisms

Advances in Materials Science and Engineering 13

from asperity deformation to the crack initiationand propagation which is a critical damage duringPSR On the other hand the wear volume and scararea were increased significantly by time duringGSR but the degradation evolutions were combinedand repeated with the mentioned wear mechanismsin a whole fretting process

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

e first author would like to acknowledge the scholarshipsupport from China Scholarship Council (CSC) is workwas supported by the Aeronautical Science Fund of China(Grant no 20164058002) National Natural Science Foun-dation of China (Grant No51735006) and Tsinghua Uni-versity Initiative Scientific Research Program

References

[1] R B Waterhouse ldquoFretting wearrdquo Wear vol 100 no 1ndash3pp 107ndash118 1984

[2] M Varenberg I Etsion and G Halperin ldquoSlip index a newunified approach to frettingrdquo Tribology Letters vol 17 no 3pp 569ndash573 2004

[3] O Vingsbo and S Soderberg ldquoOn fretting mapsrdquo Wearvol 126 no 2 pp 131ndash147 1988

[4] R D Mindlin and H Deresiewiez ldquoElastic spheres in contactunder varying oblique forcesrdquo Journal of Applied Mechanicsvol 20 pp 327ndash344 1953

[5] Z R Zhou and L Vincent ldquoMixed fretting regimerdquo Wearvol 181ndash183 pp 531ndash536 1995

[6] S Fouvry P Kapsa and L Vincent ldquoQuantification offretting damagerdquo Wear vol 200 no 1-2 pp 186ndash205 1996

[7] J Yu L Qian B Yu and Z Zhou ldquoNanofretting behavior ofmonocrystalline silicon (100) against SiO2 microsphere invacuumrdquo Tribology Letters vol 34 no 1 pp 31ndash40 2009

[8] H Mohrbacher J P Celis and J R Roos ldquoLaboratory testingof displacement and load induced frettingrdquo Tribology In-ternational vol 28 no 5 pp 269ndash278 1995

[9] Z R Zhou S Fayeulle and L Vincent ldquoCracking behaviourof various aluminium alloys during fretting wearrdquo Wearvol 155 no 2 pp 317ndash330 1992

[10] S Fouvry P Kapsa H Zahouani and L Vincent ldquoWearanalysis in fretting of hard coatings through a dissipatedenergy conceptrdquo Wear vol 203-204 pp 393ndash403 1997

[11] J Li and Y H Lu ldquoEffects of displacement amplitude onfretting wear behaviors and mechanism of Inconel 600 alloyrdquoWear vol 304 no 1-2 pp 223ndash230 2013

[12] G B Stachowiak and G W Stachowiak ldquoFretting wear andfriction behaviour of engineering ceramicsrdquo Wear vol 190no 2 pp 212ndash218 1995

[13] B Bhushan and B K Gupta Handbook of Tribology Mate-rials Coatings and Surface Treatments McGraw-Hill NewYork NY USA 1991

[14] H Y Zhang Y H Lu M Ma and J Li ldquoEffect of precipitatedcarbides on the fretting wear behavior of Inconel 600 alloyrdquoWear vol 315 no 1-2 pp 58ndash67 2014

[15] X Mi W X Wang X M Xiong et al ldquoInvestigation offretting wear behavior of Inconel 690 alloy in tubeplatecontact configurationrdquoWear vol 328-329 pp 582ndash590 2015

[16] L Jie L Yonghao Z Haoyang and L Xin ldquoEffect of grain sizeand hardness on fretting wear behavior of inconel 600 alloysrdquoTribology International vol 81 pp 215ndash222 2015

[17] L Xin B B Yang Z H Wang J Li Y H Lu and T ShojildquoMicrostructural evolution of subsurface on inconel 690TTalloy subjected to fretting wear at elevated temperaturerdquoMaterials amp Design vol 104 pp 152ndash161 2016

[18] J Li B B Yang Y H Lu L Xin Z H Wang and T Shojildquoe degradation mechanism of inconel 690TT induced byfretting wear in airrdquo Tribology International vol 116pp 147ndash154 2017

[19] G Xianglong L Ping T Lichen et al ldquoEffects of slidingamplitude and normal load on the fretting wear behavior ofalloy 690 tube exposed to high temperature waterrdquo TribologyInternational vol 116 pp 155ndash163 2017

[20] Special Metals INCONEL alloy X-750 Data Sheet 2004Publication No SMC-067 httpwwwspecialmetalscom

[21] C Marsh S Depinoy and D Kaoumi ldquoEffect of heattreatment on the temperature dependence of the fracturebehavior of X-750 alloyrdquo Materials Science and EngineeringA vol 677 pp 474ndash484 2016

[22] D Wenbo S Yanhua D Chunhua and Y Lie ldquoStructuralstiffness of X-750 alloy bump foil strips for compliant foilbearings with different heat treatmentsrdquo Journal of Tribologyvol 138 no 3 article 031702 2016

[23] G X Chen and Z R Zhou ldquoStudy on transition betweenfretting and reciprocating sliding wearrdquo Wear vol 250no 1ndash12 pp 665ndash672 2001

[24] J F Archard ldquoContact and rubbing of flat surfacesrdquo Journal ofApplied Physics vol 24 no 8 pp 981ndash988 1953

[25] S C Lim M F Ashby and J H Brunton ldquoWear-ratetransitions and their relationship to wear mechanismsrdquoActa Metallurgica vol 35 no 6 pp 1343ndash1348 1987

[26] S C Lim ldquoRecent developments in wear-mechanism mapsrdquoTribology International vol 31 no 1ndash3 pp 87ndash97 1998

[27] X LongW Zihao L Jie Y Lu and T Shoji ldquoMicrostructuralcharacterization of subsurface caused by fretting wear ofinconel 690TT alloyrdquo Material Characteristics vol 115pp 32ndash38 2016

[28] R Rybiak S Fouvry and B Bonnet ldquoFretting wear of stainlesssteels under variable temperature conditions introduction ofa ldquocompositerdquo wear lawrdquoWear vol 268 no 3-4 pp 413ndash4232010

[29] J F Zheng J Luo J L Mo J F Peng X S Jin andMH ZhuldquoFretting wear behaviors of a railway axle steelrdquo TribologyInternational vol 43 no 5-6 pp 906ndash911 2010

[30] K V Virendra N Hamza S S R Ganesh H MurthyA N Majila and D C Fernando ldquoEffect of contact pressureand stress ratio on the fretting fatigue behaviour of Ti-6Al-4Vrdquo Material Science and Engineering A vol 707 pp 647ndash656 2017

[31] J J Madge S B Leen and P H Shipway ldquoe critical role offretting wear in the analysis of fretting fatiguerdquoWear vol 263no 1ndash6 pp 542ndash551 2007

14 Advances in Materials Science and Engineering

attributed to galling and scuordfng [13] Figure 11(b) shows themagnied image in Figure 11(a) that the crack propagationswere prevented by particle detachment and started to spall

eventually becoming loose wear debris Fretted surfaces wererough owing to the plastic deformation and ploughing ef-fects and in some cases surface roughening would provide

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(a)

100

75

50

25

0

ndash25

ndash50

ndash75

ndash100ndash60 ndash40 ndash20 0

40μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

20 40 60

120

90

60

30

0

ndash30

ndash60

ndash90

ndash120ndash120 ndash90 ndash60 ndash30 0

100μm

Displacement amplitude (μm)

Tang

entia

l for

ce (N

)

30 60 90 120

(b)

Figure 9 Evolution of fretting loops for 40 microm and 100 microm after (a) 5 and (b) 90minutes of fretting

125100075050025000

ndash025ndash050ndash075ndash100ndash125

60001 60002 60003Time (s)

Coef

ficie

nt o

f fric

tion

60004 60005

40microm

(a)

Time (s)

125100075050025000

ndash025ndash050ndash075ndash100ndash125

Coef

ficie

nt o

f fric

tion

100microm

60001 60002 60003 60004 60005

(b)

Figure 8 Sinusoidal coeordfcient of frictions during 600 s fretting time for (a) 40 microm and (b) 100 microm

Advances in Materials Science and Engineering 9

escape channels for wear debris As the fretting test con-tinued the contact interfaces were slowly accommodated bythe plastic flow and further loading promoted the growth ofsubsurface cracks that parallel to the surface When thesecracks finally extended out to the free surface thin platelet-like wear particles delaminated as shown in Figures 11(c)and 11(d) In the same time when the delamination wasoccurring mostly in the contact center plastic flow of thecontacting surfaces in the periphery and third-body flowclose to the contact border were observed in Figures 11(e)and 11(f) respectively Moreover as temperature increasesbecause of frictional heating during GSR oxidation of thewear particles becomes more ubiquitous and as a

consequence thicker more continuous oxide layer will begenerated e greater contact temperature at this conditionalso causes plastic flow of the oxide film leading to moresevere oxidational wear [19]

Figure 12 shows the SEM images of wear scars andcorresponding 3D surface topographies of the steel ballsoscillated at 40 microm and 100 microm after 90minutes of frettingBoth wear scars were in a circular shape e worn surfacearea which was oscillated at 40 microm also contains the stickdomain in the contact center and slip domain at the pe-riphery as shown in Figure 12(a) However it is clear fromthe picture that a bulk of oxidized X-750 alloy surface layerin black was adhered to the half annulus of the contact which

Slip region

Stick region

Micropitboundary

Slip region

Adhesive microslip

(a)

Stick region

Microcracks

Slip region

Adhesive layerremoval

Crack delamination

(b)

Stick region

Cracks

Slip region

New crack growth alongthe contact border

(c)

Figure 10 SEMmicrographs of Inconel X-750 wear scars during PSR (a) after 10minutes (b) after 30minutes and (c) after 90minutes offretting Displacement amplitude is 40 microm Double arrows represent fretting direction

10 Advances in Materials Science and Engineering

was believed to be plucked off by harder GCr15 ball surfaceduring fretting induced by fatigue According to the wearscar in Figure 12(b) GSR was dominant at 100 microm with thesign of abrasion and small amount of transferred materialson the worn surface Figure 13 shows the EDX spectruminformation for the marked spots in Figure 12 on the wearscar areas Oxide content was very low (146 wt) in thestick region due to the constriction of the relative motionwhile microslip region was reacting with the oxygen in asmall amount On the other hand the highly concentratedoxygen content (29 wt) was detected on the transferredflat material in Figure 13(c) However the oxidation process

on the worn steel surface was faster during GSR rather thanPSR (Figure 13(d))

4 Discussion

e fretting wear process in an ambient temperature is oftendetermined by the contact geometry the oxidation processand the subsequent third-body behavior in the contact in-terface which significantly affect the friction and wearproperties in dry air [11 16 27] Wear properties such asvolume scar area and depth were considerably lowerduring PSR than GSR as shown in Figures 3ndash6 because of

(b)

Adhesive shear

Plowing

(a)

Crack spalling

(b)

Delamination

(c)

Delamination

Oxide layers

(d)

Plastic flow

(e)

Oxidized third-body flow

(f )

Figure 11 SEMmicrographs of Inconel X-750 wear scars during GSR (a) mixed abrasive and adhesive wear at the onset of fretting process(b) spalling of cracks (c d) delamination (e) plastic flow and (f) third-body flow near contact border Displacement amplitude is 100 micromDouble arrows represent fretting direction

Advances in Materials Science and Engineering 11

the small imposed contact area compared to the scale of thenormal load applied Yet the wear rate was maximum in therunning-in period for both cases decreasing gradually withfretting time in Figure 6(c) typically due to the formation ofthe oxide layer (also ldquoglazerdquo layer) on the worn surface which

can enhance the load-carrying capacity avoiding furtherwear [28] During the partial and gross slip conditions thefriction is the outcome of the direct interlocking of thesurface asperities and the trapped oxide debris behavior inthe contact interface respectively In Figure 7 the COF

Highly oxidized Inconel X-750alloy wear layer transfer

a b c

(a)

d

Oxidization

(b)

Figure 12 SEM morphologies of GCr15 steel ball worn scars oscillating at (a) 40 microm and (b) 100 microm Fretting time is 90minutes Doublearrows represent fretting direction

C

O

Fe

Ni SiPt CrMn

Fe

Ni

O KCr KFe KNi K

Element0653wt

019687490056

1888at

017572460044

00

06

12

17

23

29

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(a)

CO

Fe

NiSiPt Cr Mn

Fe

Ni

O KCr KFe KNi K

Element0146wt

026391270104

0470at

026184190091

200 300 400 500 600 700 800 900 10100Energy (keV)

00

05

10

16

21

26

KCnt

(b)

O KCr KFe KNi K

Element2959wt

107305115105

5793at

064702732863

C

O

FeNi SiPt

Cr

Mn Fe

Ni

00

06

12

18

24

30

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(c)

O KCr KFe KNi K

Element1499wt

020378570071

3572at

014953640046

C

O

FeNi

SiPt CrMn

Fe

Ni

200 300 400 500 600 700 800 900 10100Energy (keV)

00

04

09

13

18

22

KCnt

(d)

Figure 13 EDX spectroscopy analysis for worn surfaces at marked spots in Figure 12

12 Advances in Materials Science and Engineering

during PSR was always lower with no apparent fluctuationduring the steady-stage level due to the minimum tangentialforce between the contact interfaces where the central zoneswere mechanically interlocked In this case the highernormal load triggers the traction coefficient where thecritical total sliding shear force is always higher than thetangential force [5 11] However in GSR the highest peak offriction occurred prior to the fluctuating steady-stage levelmainly due to the strong plastic deformation of work-hardened layer of the contacting surfaces [23 29] On theother hand the fluctuations in COF are attributed to themodifications in the contact interface which are linked to thethird-body rheology ie wear debris formation and itsentrapment and ejection from the contact zone [27]

e fretting loops generated by Ft-D curves in Figure 9are good indicators to show the slip condition at any mo-ment e area enclosed by the curves is the measure ofdissipated energy produced by friction [10 30] e frictionwork performed provides a more representative explanationof the surface damage Usually it has been noticed that thewear volume V is proportional to the energy dissipated Edin the contact and described as V αtimes 1113936Ed where α is thefriction energy wear coefficient [6] e degree of slope Sccan be considered as wear characteristics of the slidingconditions and materials Besides the unified slip indexapproach also offers the knowledge of fretting conditionsand considered as an appropriate means for estimatingfretting wear problems In accordance with the terms of slipindex when the slip ratio s⟶ 0 the contacts are in stickand as the slip ratio approaches to 1 partial slip and thengross slip prevail [2] e partial slip contacts in smalldisplacements induce cyclic stresses which favor cracknucleation and propagation but the loading condition isnondissipative with limited surface damage at the peripheryas shown in Figure 10 However the friction dissipation inGSR correlated with the plastic flow delamination andoxidation wear mechanisms causes a large amount ofsurface damage by extending the contact area and reducingthe contact pressure profile (Figure 11)

e main damage mechanisms ie cracking (frettinginduced by fatigue) and material loss (fretting induced bywear) are often appear as a competing process which wasextensively explored during the last decade [1 3 5 6 31ndash34]For instance the material loss during GSR can eliminatesmall cracks or fill up the opening of a deep crack andaccommodate the main portion of the imposed displace-ment as a consequence it strongly reduces the slip am-plitude and then the debris formation In fact the debrisejection has great impact on the third-body establishment ifit is trapped between the contacts the degradation processcan be suppressed and the most of the velocity differencebetween the friction pairs would be completely accommo-dated in a dissipative manner by the powder bed [33 34] Asfor cracking the effects of frictional force and the contactload are huge on the crack initiation and growth duringfretting fatigue where the frictional force triggers the crackinitiation while the contact load disrupts the crack growthduring the propagation period [37] Meanwhile it is re-ported that the cracks on the worn scar surface nucleated

and propagated along the direction of 30ndash50deg to the surfaceinterior which was in the range of calculated maximumshear stress angle [18]

SEM morphology in Figure 12(a) shows the interestingwear phenomenon where the thick layer of Inconel X-750alloy was stuck to the worn surface of the oscillating ball dueto the adhesive microslip In return with the further frettingthe material transferred to the surface of GCr14 ball has thehighest possibility to transfer back to the previous wornsurface of Inconel X-750 alloy [8] Besides the transferredwear layer was highly oxidized compared to the stick and slipregions of the steel ball as shown in Figure 13 e debrisdetached from the contact pairs is essentially composed ofnonmagnetic single component oxides eg Fe2O3 NiO andCr2O3 or more complex oxides eg NiCr2O4 and NiFe2O4[38] However the oxidization process was rapid on theworn surface of the steel ball during GSR which is because ofmore mechanical energy being converted to the thermalheat and it is believed that the frictional heat during GSRwas higher than in PSR [19]

5 Conclusion

e main purpose of this study was to explore the degra-dation evolutions of Inconel X-750 co-acted with GCr15steel ball through the dry fretting tests and observationsanalyses by using 3D surface profiler SEM and EDXAccording to the results the conclusions can be drawn asfollows

(i) e degradation mechanisms of Inconel X-750 weretotally dependent on the fretting regimes and variedwith the fretting time

(ii) e wear volume and wear depth were very low inPSR and wear mechanisms were associated with thedeformations adhesion and fatigue crack emicrocracks were present around the stick domainin 3times104 cycle and the radial cracks fully coveredthe contact center above 105 cycle along with thebigger crack in the contact border e large layer ofductile X-750 alloy was transferred to the wearsurface of the steel ball due to the exhaustion byhighly concentrated cyclic loading during the laterstages of fretting

(iii) In GSR the degradation mechanisms were as fol-lows (1) adhesive wear (galling and scuffing) (2)abrasive wear by third-body particle which is amechanical removal process (3) delaminationwhich is influenced by the material fatigue in theshallow subsurface layer and (4) oxidation of debrisparticles and surface layer due to the higher fric-tional heat which can enhance the load-carryingcapacity as well as reduce the wear rate in the laterstages of fretting process

(iv) e dependence of fretting time was negligibleduring PSR in respect of wear properties such aswear volume scar area and depth However it has agreat impact to evolve the degradation mechanisms

Advances in Materials Science and Engineering 13

from asperity deformation to the crack initiationand propagation which is a critical damage duringPSR On the other hand the wear volume and scararea were increased significantly by time duringGSR but the degradation evolutions were combinedand repeated with the mentioned wear mechanismsin a whole fretting process

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

e first author would like to acknowledge the scholarshipsupport from China Scholarship Council (CSC) is workwas supported by the Aeronautical Science Fund of China(Grant no 20164058002) National Natural Science Foun-dation of China (Grant No51735006) and Tsinghua Uni-versity Initiative Scientific Research Program

References

[1] R B Waterhouse ldquoFretting wearrdquo Wear vol 100 no 1ndash3pp 107ndash118 1984

[2] M Varenberg I Etsion and G Halperin ldquoSlip index a newunified approach to frettingrdquo Tribology Letters vol 17 no 3pp 569ndash573 2004

[3] O Vingsbo and S Soderberg ldquoOn fretting mapsrdquo Wearvol 126 no 2 pp 131ndash147 1988

[4] R D Mindlin and H Deresiewiez ldquoElastic spheres in contactunder varying oblique forcesrdquo Journal of Applied Mechanicsvol 20 pp 327ndash344 1953

[5] Z R Zhou and L Vincent ldquoMixed fretting regimerdquo Wearvol 181ndash183 pp 531ndash536 1995

[6] S Fouvry P Kapsa and L Vincent ldquoQuantification offretting damagerdquo Wear vol 200 no 1-2 pp 186ndash205 1996

[7] J Yu L Qian B Yu and Z Zhou ldquoNanofretting behavior ofmonocrystalline silicon (100) against SiO2 microsphere invacuumrdquo Tribology Letters vol 34 no 1 pp 31ndash40 2009

[8] H Mohrbacher J P Celis and J R Roos ldquoLaboratory testingof displacement and load induced frettingrdquo Tribology In-ternational vol 28 no 5 pp 269ndash278 1995

[9] Z R Zhou S Fayeulle and L Vincent ldquoCracking behaviourof various aluminium alloys during fretting wearrdquo Wearvol 155 no 2 pp 317ndash330 1992

[10] S Fouvry P Kapsa H Zahouani and L Vincent ldquoWearanalysis in fretting of hard coatings through a dissipatedenergy conceptrdquo Wear vol 203-204 pp 393ndash403 1997

[11] J Li and Y H Lu ldquoEffects of displacement amplitude onfretting wear behaviors and mechanism of Inconel 600 alloyrdquoWear vol 304 no 1-2 pp 223ndash230 2013

[12] G B Stachowiak and G W Stachowiak ldquoFretting wear andfriction behaviour of engineering ceramicsrdquo Wear vol 190no 2 pp 212ndash218 1995

[13] B Bhushan and B K Gupta Handbook of Tribology Mate-rials Coatings and Surface Treatments McGraw-Hill NewYork NY USA 1991

[14] H Y Zhang Y H Lu M Ma and J Li ldquoEffect of precipitatedcarbides on the fretting wear behavior of Inconel 600 alloyrdquoWear vol 315 no 1-2 pp 58ndash67 2014

[15] X Mi W X Wang X M Xiong et al ldquoInvestigation offretting wear behavior of Inconel 690 alloy in tubeplatecontact configurationrdquoWear vol 328-329 pp 582ndash590 2015

[16] L Jie L Yonghao Z Haoyang and L Xin ldquoEffect of grain sizeand hardness on fretting wear behavior of inconel 600 alloysrdquoTribology International vol 81 pp 215ndash222 2015

[17] L Xin B B Yang Z H Wang J Li Y H Lu and T ShojildquoMicrostructural evolution of subsurface on inconel 690TTalloy subjected to fretting wear at elevated temperaturerdquoMaterials amp Design vol 104 pp 152ndash161 2016

[18] J Li B B Yang Y H Lu L Xin Z H Wang and T Shojildquoe degradation mechanism of inconel 690TT induced byfretting wear in airrdquo Tribology International vol 116pp 147ndash154 2017

[19] G Xianglong L Ping T Lichen et al ldquoEffects of slidingamplitude and normal load on the fretting wear behavior ofalloy 690 tube exposed to high temperature waterrdquo TribologyInternational vol 116 pp 155ndash163 2017

[20] Special Metals INCONEL alloy X-750 Data Sheet 2004Publication No SMC-067 httpwwwspecialmetalscom

[21] C Marsh S Depinoy and D Kaoumi ldquoEffect of heattreatment on the temperature dependence of the fracturebehavior of X-750 alloyrdquo Materials Science and EngineeringA vol 677 pp 474ndash484 2016

[22] D Wenbo S Yanhua D Chunhua and Y Lie ldquoStructuralstiffness of X-750 alloy bump foil strips for compliant foilbearings with different heat treatmentsrdquo Journal of Tribologyvol 138 no 3 article 031702 2016

[23] G X Chen and Z R Zhou ldquoStudy on transition betweenfretting and reciprocating sliding wearrdquo Wear vol 250no 1ndash12 pp 665ndash672 2001

[24] J F Archard ldquoContact and rubbing of flat surfacesrdquo Journal ofApplied Physics vol 24 no 8 pp 981ndash988 1953

[25] S C Lim M F Ashby and J H Brunton ldquoWear-ratetransitions and their relationship to wear mechanismsrdquoActa Metallurgica vol 35 no 6 pp 1343ndash1348 1987

[26] S C Lim ldquoRecent developments in wear-mechanism mapsrdquoTribology International vol 31 no 1ndash3 pp 87ndash97 1998

[27] X LongW Zihao L Jie Y Lu and T Shoji ldquoMicrostructuralcharacterization of subsurface caused by fretting wear ofinconel 690TT alloyrdquo Material Characteristics vol 115pp 32ndash38 2016

[28] R Rybiak S Fouvry and B Bonnet ldquoFretting wear of stainlesssteels under variable temperature conditions introduction ofa ldquocompositerdquo wear lawrdquoWear vol 268 no 3-4 pp 413ndash4232010

[29] J F Zheng J Luo J L Mo J F Peng X S Jin andMH ZhuldquoFretting wear behaviors of a railway axle steelrdquo TribologyInternational vol 43 no 5-6 pp 906ndash911 2010

[30] K V Virendra N Hamza S S R Ganesh H MurthyA N Majila and D C Fernando ldquoEffect of contact pressureand stress ratio on the fretting fatigue behaviour of Ti-6Al-4Vrdquo Material Science and Engineering A vol 707 pp 647ndash656 2017

[31] J J Madge S B Leen and P H Shipway ldquoe critical role offretting wear in the analysis of fretting fatiguerdquoWear vol 263no 1ndash6 pp 542ndash551 2007

14 Advances in Materials Science and Engineering

escape channels for wear debris As the fretting test con-tinued the contact interfaces were slowly accommodated bythe plastic flow and further loading promoted the growth ofsubsurface cracks that parallel to the surface When thesecracks finally extended out to the free surface thin platelet-like wear particles delaminated as shown in Figures 11(c)and 11(d) In the same time when the delamination wasoccurring mostly in the contact center plastic flow of thecontacting surfaces in the periphery and third-body flowclose to the contact border were observed in Figures 11(e)and 11(f) respectively Moreover as temperature increasesbecause of frictional heating during GSR oxidation of thewear particles becomes more ubiquitous and as a

consequence thicker more continuous oxide layer will begenerated e greater contact temperature at this conditionalso causes plastic flow of the oxide film leading to moresevere oxidational wear [19]

Figure 12 shows the SEM images of wear scars andcorresponding 3D surface topographies of the steel ballsoscillated at 40 microm and 100 microm after 90minutes of frettingBoth wear scars were in a circular shape e worn surfacearea which was oscillated at 40 microm also contains the stickdomain in the contact center and slip domain at the pe-riphery as shown in Figure 12(a) However it is clear fromthe picture that a bulk of oxidized X-750 alloy surface layerin black was adhered to the half annulus of the contact which

Slip region

Stick region

Micropitboundary

Slip region

Adhesive microslip

(a)

Stick region

Microcracks

Slip region

Adhesive layerremoval

Crack delamination

(b)

Stick region

Cracks

Slip region

New crack growth alongthe contact border

(c)

Figure 10 SEMmicrographs of Inconel X-750 wear scars during PSR (a) after 10minutes (b) after 30minutes and (c) after 90minutes offretting Displacement amplitude is 40 microm Double arrows represent fretting direction

10 Advances in Materials Science and Engineering

was believed to be plucked off by harder GCr15 ball surfaceduring fretting induced by fatigue According to the wearscar in Figure 12(b) GSR was dominant at 100 microm with thesign of abrasion and small amount of transferred materialson the worn surface Figure 13 shows the EDX spectruminformation for the marked spots in Figure 12 on the wearscar areas Oxide content was very low (146 wt) in thestick region due to the constriction of the relative motionwhile microslip region was reacting with the oxygen in asmall amount On the other hand the highly concentratedoxygen content (29 wt) was detected on the transferredflat material in Figure 13(c) However the oxidation process

on the worn steel surface was faster during GSR rather thanPSR (Figure 13(d))

4 Discussion

e fretting wear process in an ambient temperature is oftendetermined by the contact geometry the oxidation processand the subsequent third-body behavior in the contact in-terface which significantly affect the friction and wearproperties in dry air [11 16 27] Wear properties such asvolume scar area and depth were considerably lowerduring PSR than GSR as shown in Figures 3ndash6 because of

(b)

Adhesive shear

Plowing

(a)

Crack spalling

(b)

Delamination

(c)

Delamination

Oxide layers

(d)

Plastic flow

(e)

Oxidized third-body flow

(f )

Figure 11 SEMmicrographs of Inconel X-750 wear scars during GSR (a) mixed abrasive and adhesive wear at the onset of fretting process(b) spalling of cracks (c d) delamination (e) plastic flow and (f) third-body flow near contact border Displacement amplitude is 100 micromDouble arrows represent fretting direction

Advances in Materials Science and Engineering 11

the small imposed contact area compared to the scale of thenormal load applied Yet the wear rate was maximum in therunning-in period for both cases decreasing gradually withfretting time in Figure 6(c) typically due to the formation ofthe oxide layer (also ldquoglazerdquo layer) on the worn surface which

can enhance the load-carrying capacity avoiding furtherwear [28] During the partial and gross slip conditions thefriction is the outcome of the direct interlocking of thesurface asperities and the trapped oxide debris behavior inthe contact interface respectively In Figure 7 the COF

Highly oxidized Inconel X-750alloy wear layer transfer

a b c

(a)

d

Oxidization

(b)

Figure 12 SEM morphologies of GCr15 steel ball worn scars oscillating at (a) 40 microm and (b) 100 microm Fretting time is 90minutes Doublearrows represent fretting direction

C

O

Fe

Ni SiPt CrMn

Fe

Ni

O KCr KFe KNi K

Element0653wt

019687490056

1888at

017572460044

00

06

12

17

23

29

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(a)

CO

Fe

NiSiPt Cr Mn

Fe

Ni

O KCr KFe KNi K

Element0146wt

026391270104

0470at

026184190091

200 300 400 500 600 700 800 900 10100Energy (keV)

00

05

10

16

21

26

KCnt

(b)

O KCr KFe KNi K

Element2959wt

107305115105

5793at

064702732863

C

O

FeNi SiPt

Cr

Mn Fe

Ni

00

06

12

18

24

30

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(c)

O KCr KFe KNi K

Element1499wt

020378570071

3572at

014953640046

C

O

FeNi

SiPt CrMn

Fe

Ni

200 300 400 500 600 700 800 900 10100Energy (keV)

00

04

09

13

18

22

KCnt

(d)

Figure 13 EDX spectroscopy analysis for worn surfaces at marked spots in Figure 12

12 Advances in Materials Science and Engineering

during PSR was always lower with no apparent fluctuationduring the steady-stage level due to the minimum tangentialforce between the contact interfaces where the central zoneswere mechanically interlocked In this case the highernormal load triggers the traction coefficient where thecritical total sliding shear force is always higher than thetangential force [5 11] However in GSR the highest peak offriction occurred prior to the fluctuating steady-stage levelmainly due to the strong plastic deformation of work-hardened layer of the contacting surfaces [23 29] On theother hand the fluctuations in COF are attributed to themodifications in the contact interface which are linked to thethird-body rheology ie wear debris formation and itsentrapment and ejection from the contact zone [27]

e fretting loops generated by Ft-D curves in Figure 9are good indicators to show the slip condition at any mo-ment e area enclosed by the curves is the measure ofdissipated energy produced by friction [10 30] e frictionwork performed provides a more representative explanationof the surface damage Usually it has been noticed that thewear volume V is proportional to the energy dissipated Edin the contact and described as V αtimes 1113936Ed where α is thefriction energy wear coefficient [6] e degree of slope Sccan be considered as wear characteristics of the slidingconditions and materials Besides the unified slip indexapproach also offers the knowledge of fretting conditionsand considered as an appropriate means for estimatingfretting wear problems In accordance with the terms of slipindex when the slip ratio s⟶ 0 the contacts are in stickand as the slip ratio approaches to 1 partial slip and thengross slip prevail [2] e partial slip contacts in smalldisplacements induce cyclic stresses which favor cracknucleation and propagation but the loading condition isnondissipative with limited surface damage at the peripheryas shown in Figure 10 However the friction dissipation inGSR correlated with the plastic flow delamination andoxidation wear mechanisms causes a large amount ofsurface damage by extending the contact area and reducingthe contact pressure profile (Figure 11)

e main damage mechanisms ie cracking (frettinginduced by fatigue) and material loss (fretting induced bywear) are often appear as a competing process which wasextensively explored during the last decade [1 3 5 6 31ndash34]For instance the material loss during GSR can eliminatesmall cracks or fill up the opening of a deep crack andaccommodate the main portion of the imposed displace-ment as a consequence it strongly reduces the slip am-plitude and then the debris formation In fact the debrisejection has great impact on the third-body establishment ifit is trapped between the contacts the degradation processcan be suppressed and the most of the velocity differencebetween the friction pairs would be completely accommo-dated in a dissipative manner by the powder bed [33 34] Asfor cracking the effects of frictional force and the contactload are huge on the crack initiation and growth duringfretting fatigue where the frictional force triggers the crackinitiation while the contact load disrupts the crack growthduring the propagation period [37] Meanwhile it is re-ported that the cracks on the worn scar surface nucleated

and propagated along the direction of 30ndash50deg to the surfaceinterior which was in the range of calculated maximumshear stress angle [18]

SEM morphology in Figure 12(a) shows the interestingwear phenomenon where the thick layer of Inconel X-750alloy was stuck to the worn surface of the oscillating ball dueto the adhesive microslip In return with the further frettingthe material transferred to the surface of GCr14 ball has thehighest possibility to transfer back to the previous wornsurface of Inconel X-750 alloy [8] Besides the transferredwear layer was highly oxidized compared to the stick and slipregions of the steel ball as shown in Figure 13 e debrisdetached from the contact pairs is essentially composed ofnonmagnetic single component oxides eg Fe2O3 NiO andCr2O3 or more complex oxides eg NiCr2O4 and NiFe2O4[38] However the oxidization process was rapid on theworn surface of the steel ball during GSR which is because ofmore mechanical energy being converted to the thermalheat and it is believed that the frictional heat during GSRwas higher than in PSR [19]

5 Conclusion

e main purpose of this study was to explore the degra-dation evolutions of Inconel X-750 co-acted with GCr15steel ball through the dry fretting tests and observationsanalyses by using 3D surface profiler SEM and EDXAccording to the results the conclusions can be drawn asfollows

(i) e degradation mechanisms of Inconel X-750 weretotally dependent on the fretting regimes and variedwith the fretting time

(ii) e wear volume and wear depth were very low inPSR and wear mechanisms were associated with thedeformations adhesion and fatigue crack emicrocracks were present around the stick domainin 3times104 cycle and the radial cracks fully coveredthe contact center above 105 cycle along with thebigger crack in the contact border e large layer ofductile X-750 alloy was transferred to the wearsurface of the steel ball due to the exhaustion byhighly concentrated cyclic loading during the laterstages of fretting

(iii) In GSR the degradation mechanisms were as fol-lows (1) adhesive wear (galling and scuffing) (2)abrasive wear by third-body particle which is amechanical removal process (3) delaminationwhich is influenced by the material fatigue in theshallow subsurface layer and (4) oxidation of debrisparticles and surface layer due to the higher fric-tional heat which can enhance the load-carryingcapacity as well as reduce the wear rate in the laterstages of fretting process

(iv) e dependence of fretting time was negligibleduring PSR in respect of wear properties such aswear volume scar area and depth However it has agreat impact to evolve the degradation mechanisms

Advances in Materials Science and Engineering 13

from asperity deformation to the crack initiationand propagation which is a critical damage duringPSR On the other hand the wear volume and scararea were increased significantly by time duringGSR but the degradation evolutions were combinedand repeated with the mentioned wear mechanismsin a whole fretting process

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

e first author would like to acknowledge the scholarshipsupport from China Scholarship Council (CSC) is workwas supported by the Aeronautical Science Fund of China(Grant no 20164058002) National Natural Science Foun-dation of China (Grant No51735006) and Tsinghua Uni-versity Initiative Scientific Research Program

References

[1] R B Waterhouse ldquoFretting wearrdquo Wear vol 100 no 1ndash3pp 107ndash118 1984

[2] M Varenberg I Etsion and G Halperin ldquoSlip index a newunified approach to frettingrdquo Tribology Letters vol 17 no 3pp 569ndash573 2004

[3] O Vingsbo and S Soderberg ldquoOn fretting mapsrdquo Wearvol 126 no 2 pp 131ndash147 1988

[4] R D Mindlin and H Deresiewiez ldquoElastic spheres in contactunder varying oblique forcesrdquo Journal of Applied Mechanicsvol 20 pp 327ndash344 1953

[5] Z R Zhou and L Vincent ldquoMixed fretting regimerdquo Wearvol 181ndash183 pp 531ndash536 1995

[6] S Fouvry P Kapsa and L Vincent ldquoQuantification offretting damagerdquo Wear vol 200 no 1-2 pp 186ndash205 1996

[7] J Yu L Qian B Yu and Z Zhou ldquoNanofretting behavior ofmonocrystalline silicon (100) against SiO2 microsphere invacuumrdquo Tribology Letters vol 34 no 1 pp 31ndash40 2009

[8] H Mohrbacher J P Celis and J R Roos ldquoLaboratory testingof displacement and load induced frettingrdquo Tribology In-ternational vol 28 no 5 pp 269ndash278 1995

[9] Z R Zhou S Fayeulle and L Vincent ldquoCracking behaviourof various aluminium alloys during fretting wearrdquo Wearvol 155 no 2 pp 317ndash330 1992

[10] S Fouvry P Kapsa H Zahouani and L Vincent ldquoWearanalysis in fretting of hard coatings through a dissipatedenergy conceptrdquo Wear vol 203-204 pp 393ndash403 1997

[11] J Li and Y H Lu ldquoEffects of displacement amplitude onfretting wear behaviors and mechanism of Inconel 600 alloyrdquoWear vol 304 no 1-2 pp 223ndash230 2013

[12] G B Stachowiak and G W Stachowiak ldquoFretting wear andfriction behaviour of engineering ceramicsrdquo Wear vol 190no 2 pp 212ndash218 1995

[13] B Bhushan and B K Gupta Handbook of Tribology Mate-rials Coatings and Surface Treatments McGraw-Hill NewYork NY USA 1991

[14] H Y Zhang Y H Lu M Ma and J Li ldquoEffect of precipitatedcarbides on the fretting wear behavior of Inconel 600 alloyrdquoWear vol 315 no 1-2 pp 58ndash67 2014

[15] X Mi W X Wang X M Xiong et al ldquoInvestigation offretting wear behavior of Inconel 690 alloy in tubeplatecontact configurationrdquoWear vol 328-329 pp 582ndash590 2015

[16] L Jie L Yonghao Z Haoyang and L Xin ldquoEffect of grain sizeand hardness on fretting wear behavior of inconel 600 alloysrdquoTribology International vol 81 pp 215ndash222 2015

[17] L Xin B B Yang Z H Wang J Li Y H Lu and T ShojildquoMicrostructural evolution of subsurface on inconel 690TTalloy subjected to fretting wear at elevated temperaturerdquoMaterials amp Design vol 104 pp 152ndash161 2016

[18] J Li B B Yang Y H Lu L Xin Z H Wang and T Shojildquoe degradation mechanism of inconel 690TT induced byfretting wear in airrdquo Tribology International vol 116pp 147ndash154 2017

[19] G Xianglong L Ping T Lichen et al ldquoEffects of slidingamplitude and normal load on the fretting wear behavior ofalloy 690 tube exposed to high temperature waterrdquo TribologyInternational vol 116 pp 155ndash163 2017

[20] Special Metals INCONEL alloy X-750 Data Sheet 2004Publication No SMC-067 httpwwwspecialmetalscom

[21] C Marsh S Depinoy and D Kaoumi ldquoEffect of heattreatment on the temperature dependence of the fracturebehavior of X-750 alloyrdquo Materials Science and EngineeringA vol 677 pp 474ndash484 2016

[22] D Wenbo S Yanhua D Chunhua and Y Lie ldquoStructuralstiffness of X-750 alloy bump foil strips for compliant foilbearings with different heat treatmentsrdquo Journal of Tribologyvol 138 no 3 article 031702 2016

[23] G X Chen and Z R Zhou ldquoStudy on transition betweenfretting and reciprocating sliding wearrdquo Wear vol 250no 1ndash12 pp 665ndash672 2001

[24] J F Archard ldquoContact and rubbing of flat surfacesrdquo Journal ofApplied Physics vol 24 no 8 pp 981ndash988 1953

[25] S C Lim M F Ashby and J H Brunton ldquoWear-ratetransitions and their relationship to wear mechanismsrdquoActa Metallurgica vol 35 no 6 pp 1343ndash1348 1987

[26] S C Lim ldquoRecent developments in wear-mechanism mapsrdquoTribology International vol 31 no 1ndash3 pp 87ndash97 1998

[27] X LongW Zihao L Jie Y Lu and T Shoji ldquoMicrostructuralcharacterization of subsurface caused by fretting wear ofinconel 690TT alloyrdquo Material Characteristics vol 115pp 32ndash38 2016

[28] R Rybiak S Fouvry and B Bonnet ldquoFretting wear of stainlesssteels under variable temperature conditions introduction ofa ldquocompositerdquo wear lawrdquoWear vol 268 no 3-4 pp 413ndash4232010

[29] J F Zheng J Luo J L Mo J F Peng X S Jin andMH ZhuldquoFretting wear behaviors of a railway axle steelrdquo TribologyInternational vol 43 no 5-6 pp 906ndash911 2010

[30] K V Virendra N Hamza S S R Ganesh H MurthyA N Majila and D C Fernando ldquoEffect of contact pressureand stress ratio on the fretting fatigue behaviour of Ti-6Al-4Vrdquo Material Science and Engineering A vol 707 pp 647ndash656 2017

[31] J J Madge S B Leen and P H Shipway ldquoe critical role offretting wear in the analysis of fretting fatiguerdquoWear vol 263no 1ndash6 pp 542ndash551 2007

14 Advances in Materials Science and Engineering

was believed to be plucked off by harder GCr15 ball surfaceduring fretting induced by fatigue According to the wearscar in Figure 12(b) GSR was dominant at 100 microm with thesign of abrasion and small amount of transferred materialson the worn surface Figure 13 shows the EDX spectruminformation for the marked spots in Figure 12 on the wearscar areas Oxide content was very low (146 wt) in thestick region due to the constriction of the relative motionwhile microslip region was reacting with the oxygen in asmall amount On the other hand the highly concentratedoxygen content (29 wt) was detected on the transferredflat material in Figure 13(c) However the oxidation process

on the worn steel surface was faster during GSR rather thanPSR (Figure 13(d))

4 Discussion

e fretting wear process in an ambient temperature is oftendetermined by the contact geometry the oxidation processand the subsequent third-body behavior in the contact in-terface which significantly affect the friction and wearproperties in dry air [11 16 27] Wear properties such asvolume scar area and depth were considerably lowerduring PSR than GSR as shown in Figures 3ndash6 because of

(b)

Adhesive shear

Plowing

(a)

Crack spalling

(b)

Delamination

(c)

Delamination

Oxide layers

(d)

Plastic flow

(e)

Oxidized third-body flow

(f )

Figure 11 SEMmicrographs of Inconel X-750 wear scars during GSR (a) mixed abrasive and adhesive wear at the onset of fretting process(b) spalling of cracks (c d) delamination (e) plastic flow and (f) third-body flow near contact border Displacement amplitude is 100 micromDouble arrows represent fretting direction

Advances in Materials Science and Engineering 11

the small imposed contact area compared to the scale of thenormal load applied Yet the wear rate was maximum in therunning-in period for both cases decreasing gradually withfretting time in Figure 6(c) typically due to the formation ofthe oxide layer (also ldquoglazerdquo layer) on the worn surface which

can enhance the load-carrying capacity avoiding furtherwear [28] During the partial and gross slip conditions thefriction is the outcome of the direct interlocking of thesurface asperities and the trapped oxide debris behavior inthe contact interface respectively In Figure 7 the COF

Highly oxidized Inconel X-750alloy wear layer transfer

a b c

(a)

d

Oxidization

(b)

Figure 12 SEM morphologies of GCr15 steel ball worn scars oscillating at (a) 40 microm and (b) 100 microm Fretting time is 90minutes Doublearrows represent fretting direction

C

O

Fe

Ni SiPt CrMn

Fe

Ni

O KCr KFe KNi K

Element0653wt

019687490056

1888at

017572460044

00

06

12

17

23

29

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(a)

CO

Fe

NiSiPt Cr Mn

Fe

Ni

O KCr KFe KNi K

Element0146wt

026391270104

0470at

026184190091

200 300 400 500 600 700 800 900 10100Energy (keV)

00

05

10

16

21

26

KCnt

(b)

O KCr KFe KNi K

Element2959wt

107305115105

5793at

064702732863

C

O

FeNi SiPt

Cr

Mn Fe

Ni

00

06

12

18

24

30

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(c)

O KCr KFe KNi K

Element1499wt

020378570071

3572at

014953640046

C

O

FeNi

SiPt CrMn

Fe

Ni

200 300 400 500 600 700 800 900 10100Energy (keV)

00

04

09

13

18

22

KCnt

(d)

Figure 13 EDX spectroscopy analysis for worn surfaces at marked spots in Figure 12

12 Advances in Materials Science and Engineering

during PSR was always lower with no apparent fluctuationduring the steady-stage level due to the minimum tangentialforce between the contact interfaces where the central zoneswere mechanically interlocked In this case the highernormal load triggers the traction coefficient where thecritical total sliding shear force is always higher than thetangential force [5 11] However in GSR the highest peak offriction occurred prior to the fluctuating steady-stage levelmainly due to the strong plastic deformation of work-hardened layer of the contacting surfaces [23 29] On theother hand the fluctuations in COF are attributed to themodifications in the contact interface which are linked to thethird-body rheology ie wear debris formation and itsentrapment and ejection from the contact zone [27]

e fretting loops generated by Ft-D curves in Figure 9are good indicators to show the slip condition at any mo-ment e area enclosed by the curves is the measure ofdissipated energy produced by friction [10 30] e frictionwork performed provides a more representative explanationof the surface damage Usually it has been noticed that thewear volume V is proportional to the energy dissipated Edin the contact and described as V αtimes 1113936Ed where α is thefriction energy wear coefficient [6] e degree of slope Sccan be considered as wear characteristics of the slidingconditions and materials Besides the unified slip indexapproach also offers the knowledge of fretting conditionsand considered as an appropriate means for estimatingfretting wear problems In accordance with the terms of slipindex when the slip ratio s⟶ 0 the contacts are in stickand as the slip ratio approaches to 1 partial slip and thengross slip prevail [2] e partial slip contacts in smalldisplacements induce cyclic stresses which favor cracknucleation and propagation but the loading condition isnondissipative with limited surface damage at the peripheryas shown in Figure 10 However the friction dissipation inGSR correlated with the plastic flow delamination andoxidation wear mechanisms causes a large amount ofsurface damage by extending the contact area and reducingthe contact pressure profile (Figure 11)

e main damage mechanisms ie cracking (frettinginduced by fatigue) and material loss (fretting induced bywear) are often appear as a competing process which wasextensively explored during the last decade [1 3 5 6 31ndash34]For instance the material loss during GSR can eliminatesmall cracks or fill up the opening of a deep crack andaccommodate the main portion of the imposed displace-ment as a consequence it strongly reduces the slip am-plitude and then the debris formation In fact the debrisejection has great impact on the third-body establishment ifit is trapped between the contacts the degradation processcan be suppressed and the most of the velocity differencebetween the friction pairs would be completely accommo-dated in a dissipative manner by the powder bed [33 34] Asfor cracking the effects of frictional force and the contactload are huge on the crack initiation and growth duringfretting fatigue where the frictional force triggers the crackinitiation while the contact load disrupts the crack growthduring the propagation period [37] Meanwhile it is re-ported that the cracks on the worn scar surface nucleated

and propagated along the direction of 30ndash50deg to the surfaceinterior which was in the range of calculated maximumshear stress angle [18]

SEM morphology in Figure 12(a) shows the interestingwear phenomenon where the thick layer of Inconel X-750alloy was stuck to the worn surface of the oscillating ball dueto the adhesive microslip In return with the further frettingthe material transferred to the surface of GCr14 ball has thehighest possibility to transfer back to the previous wornsurface of Inconel X-750 alloy [8] Besides the transferredwear layer was highly oxidized compared to the stick and slipregions of the steel ball as shown in Figure 13 e debrisdetached from the contact pairs is essentially composed ofnonmagnetic single component oxides eg Fe2O3 NiO andCr2O3 or more complex oxides eg NiCr2O4 and NiFe2O4[38] However the oxidization process was rapid on theworn surface of the steel ball during GSR which is because ofmore mechanical energy being converted to the thermalheat and it is believed that the frictional heat during GSRwas higher than in PSR [19]

5 Conclusion

e main purpose of this study was to explore the degra-dation evolutions of Inconel X-750 co-acted with GCr15steel ball through the dry fretting tests and observationsanalyses by using 3D surface profiler SEM and EDXAccording to the results the conclusions can be drawn asfollows

(i) e degradation mechanisms of Inconel X-750 weretotally dependent on the fretting regimes and variedwith the fretting time

(ii) e wear volume and wear depth were very low inPSR and wear mechanisms were associated with thedeformations adhesion and fatigue crack emicrocracks were present around the stick domainin 3times104 cycle and the radial cracks fully coveredthe contact center above 105 cycle along with thebigger crack in the contact border e large layer ofductile X-750 alloy was transferred to the wearsurface of the steel ball due to the exhaustion byhighly concentrated cyclic loading during the laterstages of fretting

(iii) In GSR the degradation mechanisms were as fol-lows (1) adhesive wear (galling and scuffing) (2)abrasive wear by third-body particle which is amechanical removal process (3) delaminationwhich is influenced by the material fatigue in theshallow subsurface layer and (4) oxidation of debrisparticles and surface layer due to the higher fric-tional heat which can enhance the load-carryingcapacity as well as reduce the wear rate in the laterstages of fretting process

(iv) e dependence of fretting time was negligibleduring PSR in respect of wear properties such aswear volume scar area and depth However it has agreat impact to evolve the degradation mechanisms

Advances in Materials Science and Engineering 13

from asperity deformation to the crack initiationand propagation which is a critical damage duringPSR On the other hand the wear volume and scararea were increased significantly by time duringGSR but the degradation evolutions were combinedand repeated with the mentioned wear mechanismsin a whole fretting process

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

e first author would like to acknowledge the scholarshipsupport from China Scholarship Council (CSC) is workwas supported by the Aeronautical Science Fund of China(Grant no 20164058002) National Natural Science Foun-dation of China (Grant No51735006) and Tsinghua Uni-versity Initiative Scientific Research Program

References

[1] R B Waterhouse ldquoFretting wearrdquo Wear vol 100 no 1ndash3pp 107ndash118 1984

[2] M Varenberg I Etsion and G Halperin ldquoSlip index a newunified approach to frettingrdquo Tribology Letters vol 17 no 3pp 569ndash573 2004

[3] O Vingsbo and S Soderberg ldquoOn fretting mapsrdquo Wearvol 126 no 2 pp 131ndash147 1988

[4] R D Mindlin and H Deresiewiez ldquoElastic spheres in contactunder varying oblique forcesrdquo Journal of Applied Mechanicsvol 20 pp 327ndash344 1953

[5] Z R Zhou and L Vincent ldquoMixed fretting regimerdquo Wearvol 181ndash183 pp 531ndash536 1995

[6] S Fouvry P Kapsa and L Vincent ldquoQuantification offretting damagerdquo Wear vol 200 no 1-2 pp 186ndash205 1996

[7] J Yu L Qian B Yu and Z Zhou ldquoNanofretting behavior ofmonocrystalline silicon (100) against SiO2 microsphere invacuumrdquo Tribology Letters vol 34 no 1 pp 31ndash40 2009

[8] H Mohrbacher J P Celis and J R Roos ldquoLaboratory testingof displacement and load induced frettingrdquo Tribology In-ternational vol 28 no 5 pp 269ndash278 1995

[9] Z R Zhou S Fayeulle and L Vincent ldquoCracking behaviourof various aluminium alloys during fretting wearrdquo Wearvol 155 no 2 pp 317ndash330 1992

[10] S Fouvry P Kapsa H Zahouani and L Vincent ldquoWearanalysis in fretting of hard coatings through a dissipatedenergy conceptrdquo Wear vol 203-204 pp 393ndash403 1997

[11] J Li and Y H Lu ldquoEffects of displacement amplitude onfretting wear behaviors and mechanism of Inconel 600 alloyrdquoWear vol 304 no 1-2 pp 223ndash230 2013

[12] G B Stachowiak and G W Stachowiak ldquoFretting wear andfriction behaviour of engineering ceramicsrdquo Wear vol 190no 2 pp 212ndash218 1995

[13] B Bhushan and B K Gupta Handbook of Tribology Mate-rials Coatings and Surface Treatments McGraw-Hill NewYork NY USA 1991

[14] H Y Zhang Y H Lu M Ma and J Li ldquoEffect of precipitatedcarbides on the fretting wear behavior of Inconel 600 alloyrdquoWear vol 315 no 1-2 pp 58ndash67 2014

[15] X Mi W X Wang X M Xiong et al ldquoInvestigation offretting wear behavior of Inconel 690 alloy in tubeplatecontact configurationrdquoWear vol 328-329 pp 582ndash590 2015

[16] L Jie L Yonghao Z Haoyang and L Xin ldquoEffect of grain sizeand hardness on fretting wear behavior of inconel 600 alloysrdquoTribology International vol 81 pp 215ndash222 2015

[17] L Xin B B Yang Z H Wang J Li Y H Lu and T ShojildquoMicrostructural evolution of subsurface on inconel 690TTalloy subjected to fretting wear at elevated temperaturerdquoMaterials amp Design vol 104 pp 152ndash161 2016

[18] J Li B B Yang Y H Lu L Xin Z H Wang and T Shojildquoe degradation mechanism of inconel 690TT induced byfretting wear in airrdquo Tribology International vol 116pp 147ndash154 2017

[19] G Xianglong L Ping T Lichen et al ldquoEffects of slidingamplitude and normal load on the fretting wear behavior ofalloy 690 tube exposed to high temperature waterrdquo TribologyInternational vol 116 pp 155ndash163 2017

[20] Special Metals INCONEL alloy X-750 Data Sheet 2004Publication No SMC-067 httpwwwspecialmetalscom

[21] C Marsh S Depinoy and D Kaoumi ldquoEffect of heattreatment on the temperature dependence of the fracturebehavior of X-750 alloyrdquo Materials Science and EngineeringA vol 677 pp 474ndash484 2016

[22] D Wenbo S Yanhua D Chunhua and Y Lie ldquoStructuralstiffness of X-750 alloy bump foil strips for compliant foilbearings with different heat treatmentsrdquo Journal of Tribologyvol 138 no 3 article 031702 2016

[23] G X Chen and Z R Zhou ldquoStudy on transition betweenfretting and reciprocating sliding wearrdquo Wear vol 250no 1ndash12 pp 665ndash672 2001

[24] J F Archard ldquoContact and rubbing of flat surfacesrdquo Journal ofApplied Physics vol 24 no 8 pp 981ndash988 1953

[25] S C Lim M F Ashby and J H Brunton ldquoWear-ratetransitions and their relationship to wear mechanismsrdquoActa Metallurgica vol 35 no 6 pp 1343ndash1348 1987

[26] S C Lim ldquoRecent developments in wear-mechanism mapsrdquoTribology International vol 31 no 1ndash3 pp 87ndash97 1998

[27] X LongW Zihao L Jie Y Lu and T Shoji ldquoMicrostructuralcharacterization of subsurface caused by fretting wear ofinconel 690TT alloyrdquo Material Characteristics vol 115pp 32ndash38 2016

[28] R Rybiak S Fouvry and B Bonnet ldquoFretting wear of stainlesssteels under variable temperature conditions introduction ofa ldquocompositerdquo wear lawrdquoWear vol 268 no 3-4 pp 413ndash4232010

[29] J F Zheng J Luo J L Mo J F Peng X S Jin andMH ZhuldquoFretting wear behaviors of a railway axle steelrdquo TribologyInternational vol 43 no 5-6 pp 906ndash911 2010

[30] K V Virendra N Hamza S S R Ganesh H MurthyA N Majila and D C Fernando ldquoEffect of contact pressureand stress ratio on the fretting fatigue behaviour of Ti-6Al-4Vrdquo Material Science and Engineering A vol 707 pp 647ndash656 2017

[31] J J Madge S B Leen and P H Shipway ldquoe critical role offretting wear in the analysis of fretting fatiguerdquoWear vol 263no 1ndash6 pp 542ndash551 2007

14 Advances in Materials Science and Engineering

the small imposed contact area compared to the scale of thenormal load applied Yet the wear rate was maximum in therunning-in period for both cases decreasing gradually withfretting time in Figure 6(c) typically due to the formation ofthe oxide layer (also ldquoglazerdquo layer) on the worn surface which

can enhance the load-carrying capacity avoiding furtherwear [28] During the partial and gross slip conditions thefriction is the outcome of the direct interlocking of thesurface asperities and the trapped oxide debris behavior inthe contact interface respectively In Figure 7 the COF

Highly oxidized Inconel X-750alloy wear layer transfer

a b c

(a)

d

Oxidization

(b)

Figure 12 SEM morphologies of GCr15 steel ball worn scars oscillating at (a) 40 microm and (b) 100 microm Fretting time is 90minutes Doublearrows represent fretting direction

C

O

Fe

Ni SiPt CrMn

Fe

Ni

O KCr KFe KNi K

Element0653wt

019687490056

1888at

017572460044

00

06

12

17

23

29

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(a)

CO

Fe

NiSiPt Cr Mn

Fe

Ni

O KCr KFe KNi K

Element0146wt

026391270104

0470at

026184190091

200 300 400 500 600 700 800 900 10100Energy (keV)

00

05

10

16

21

26

KCnt

(b)

O KCr KFe KNi K

Element2959wt

107305115105

5793at

064702732863

C

O

FeNi SiPt

Cr

Mn Fe

Ni

00

06

12

18

24

30

KCnt

200 300 400 500 600 700 800 900 10100Energy (keV)

(c)

O KCr KFe KNi K

Element1499wt

020378570071

3572at

014953640046

C

O

FeNi

SiPt CrMn

Fe

Ni

200 300 400 500 600 700 800 900 10100Energy (keV)

00

04

09

13

18

22

KCnt

(d)

Figure 13 EDX spectroscopy analysis for worn surfaces at marked spots in Figure 12

12 Advances in Materials Science and Engineering

during PSR was always lower with no apparent fluctuationduring the steady-stage level due to the minimum tangentialforce between the contact interfaces where the central zoneswere mechanically interlocked In this case the highernormal load triggers the traction coefficient where thecritical total sliding shear force is always higher than thetangential force [5 11] However in GSR the highest peak offriction occurred prior to the fluctuating steady-stage levelmainly due to the strong plastic deformation of work-hardened layer of the contacting surfaces [23 29] On theother hand the fluctuations in COF are attributed to themodifications in the contact interface which are linked to thethird-body rheology ie wear debris formation and itsentrapment and ejection from the contact zone [27]

e fretting loops generated by Ft-D curves in Figure 9are good indicators to show the slip condition at any mo-ment e area enclosed by the curves is the measure ofdissipated energy produced by friction [10 30] e frictionwork performed provides a more representative explanationof the surface damage Usually it has been noticed that thewear volume V is proportional to the energy dissipated Edin the contact and described as V αtimes 1113936Ed where α is thefriction energy wear coefficient [6] e degree of slope Sccan be considered as wear characteristics of the slidingconditions and materials Besides the unified slip indexapproach also offers the knowledge of fretting conditionsand considered as an appropriate means for estimatingfretting wear problems In accordance with the terms of slipindex when the slip ratio s⟶ 0 the contacts are in stickand as the slip ratio approaches to 1 partial slip and thengross slip prevail [2] e partial slip contacts in smalldisplacements induce cyclic stresses which favor cracknucleation and propagation but the loading condition isnondissipative with limited surface damage at the peripheryas shown in Figure 10 However the friction dissipation inGSR correlated with the plastic flow delamination andoxidation wear mechanisms causes a large amount ofsurface damage by extending the contact area and reducingthe contact pressure profile (Figure 11)

e main damage mechanisms ie cracking (frettinginduced by fatigue) and material loss (fretting induced bywear) are often appear as a competing process which wasextensively explored during the last decade [1 3 5 6 31ndash34]For instance the material loss during GSR can eliminatesmall cracks or fill up the opening of a deep crack andaccommodate the main portion of the imposed displace-ment as a consequence it strongly reduces the slip am-plitude and then the debris formation In fact the debrisejection has great impact on the third-body establishment ifit is trapped between the contacts the degradation processcan be suppressed and the most of the velocity differencebetween the friction pairs would be completely accommo-dated in a dissipative manner by the powder bed [33 34] Asfor cracking the effects of frictional force and the contactload are huge on the crack initiation and growth duringfretting fatigue where the frictional force triggers the crackinitiation while the contact load disrupts the crack growthduring the propagation period [37] Meanwhile it is re-ported that the cracks on the worn scar surface nucleated

and propagated along the direction of 30ndash50deg to the surfaceinterior which was in the range of calculated maximumshear stress angle [18]

SEM morphology in Figure 12(a) shows the interestingwear phenomenon where the thick layer of Inconel X-750alloy was stuck to the worn surface of the oscillating ball dueto the adhesive microslip In return with the further frettingthe material transferred to the surface of GCr14 ball has thehighest possibility to transfer back to the previous wornsurface of Inconel X-750 alloy [8] Besides the transferredwear layer was highly oxidized compared to the stick and slipregions of the steel ball as shown in Figure 13 e debrisdetached from the contact pairs is essentially composed ofnonmagnetic single component oxides eg Fe2O3 NiO andCr2O3 or more complex oxides eg NiCr2O4 and NiFe2O4[38] However the oxidization process was rapid on theworn surface of the steel ball during GSR which is because ofmore mechanical energy being converted to the thermalheat and it is believed that the frictional heat during GSRwas higher than in PSR [19]

5 Conclusion

e main purpose of this study was to explore the degra-dation evolutions of Inconel X-750 co-acted with GCr15steel ball through the dry fretting tests and observationsanalyses by using 3D surface profiler SEM and EDXAccording to the results the conclusions can be drawn asfollows

(i) e degradation mechanisms of Inconel X-750 weretotally dependent on the fretting regimes and variedwith the fretting time

(ii) e wear volume and wear depth were very low inPSR and wear mechanisms were associated with thedeformations adhesion and fatigue crack emicrocracks were present around the stick domainin 3times104 cycle and the radial cracks fully coveredthe contact center above 105 cycle along with thebigger crack in the contact border e large layer ofductile X-750 alloy was transferred to the wearsurface of the steel ball due to the exhaustion byhighly concentrated cyclic loading during the laterstages of fretting

(iii) In GSR the degradation mechanisms were as fol-lows (1) adhesive wear (galling and scuffing) (2)abrasive wear by third-body particle which is amechanical removal process (3) delaminationwhich is influenced by the material fatigue in theshallow subsurface layer and (4) oxidation of debrisparticles and surface layer due to the higher fric-tional heat which can enhance the load-carryingcapacity as well as reduce the wear rate in the laterstages of fretting process

(iv) e dependence of fretting time was negligibleduring PSR in respect of wear properties such aswear volume scar area and depth However it has agreat impact to evolve the degradation mechanisms

Advances in Materials Science and Engineering 13

from asperity deformation to the crack initiationand propagation which is a critical damage duringPSR On the other hand the wear volume and scararea were increased significantly by time duringGSR but the degradation evolutions were combinedand repeated with the mentioned wear mechanismsin a whole fretting process

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

e first author would like to acknowledge the scholarshipsupport from China Scholarship Council (CSC) is workwas supported by the Aeronautical Science Fund of China(Grant no 20164058002) National Natural Science Foun-dation of China (Grant No51735006) and Tsinghua Uni-versity Initiative Scientific Research Program

References

[1] R B Waterhouse ldquoFretting wearrdquo Wear vol 100 no 1ndash3pp 107ndash118 1984

[2] M Varenberg I Etsion and G Halperin ldquoSlip index a newunified approach to frettingrdquo Tribology Letters vol 17 no 3pp 569ndash573 2004

[3] O Vingsbo and S Soderberg ldquoOn fretting mapsrdquo Wearvol 126 no 2 pp 131ndash147 1988

[4] R D Mindlin and H Deresiewiez ldquoElastic spheres in contactunder varying oblique forcesrdquo Journal of Applied Mechanicsvol 20 pp 327ndash344 1953

[5] Z R Zhou and L Vincent ldquoMixed fretting regimerdquo Wearvol 181ndash183 pp 531ndash536 1995

[6] S Fouvry P Kapsa and L Vincent ldquoQuantification offretting damagerdquo Wear vol 200 no 1-2 pp 186ndash205 1996

[7] J Yu L Qian B Yu and Z Zhou ldquoNanofretting behavior ofmonocrystalline silicon (100) against SiO2 microsphere invacuumrdquo Tribology Letters vol 34 no 1 pp 31ndash40 2009

[8] H Mohrbacher J P Celis and J R Roos ldquoLaboratory testingof displacement and load induced frettingrdquo Tribology In-ternational vol 28 no 5 pp 269ndash278 1995

[9] Z R Zhou S Fayeulle and L Vincent ldquoCracking behaviourof various aluminium alloys during fretting wearrdquo Wearvol 155 no 2 pp 317ndash330 1992

[10] S Fouvry P Kapsa H Zahouani and L Vincent ldquoWearanalysis in fretting of hard coatings through a dissipatedenergy conceptrdquo Wear vol 203-204 pp 393ndash403 1997

[11] J Li and Y H Lu ldquoEffects of displacement amplitude onfretting wear behaviors and mechanism of Inconel 600 alloyrdquoWear vol 304 no 1-2 pp 223ndash230 2013

[12] G B Stachowiak and G W Stachowiak ldquoFretting wear andfriction behaviour of engineering ceramicsrdquo Wear vol 190no 2 pp 212ndash218 1995

[13] B Bhushan and B K Gupta Handbook of Tribology Mate-rials Coatings and Surface Treatments McGraw-Hill NewYork NY USA 1991

[14] H Y Zhang Y H Lu M Ma and J Li ldquoEffect of precipitatedcarbides on the fretting wear behavior of Inconel 600 alloyrdquoWear vol 315 no 1-2 pp 58ndash67 2014

[15] X Mi W X Wang X M Xiong et al ldquoInvestigation offretting wear behavior of Inconel 690 alloy in tubeplatecontact configurationrdquoWear vol 328-329 pp 582ndash590 2015

[16] L Jie L Yonghao Z Haoyang and L Xin ldquoEffect of grain sizeand hardness on fretting wear behavior of inconel 600 alloysrdquoTribology International vol 81 pp 215ndash222 2015

[17] L Xin B B Yang Z H Wang J Li Y H Lu and T ShojildquoMicrostructural evolution of subsurface on inconel 690TTalloy subjected to fretting wear at elevated temperaturerdquoMaterials amp Design vol 104 pp 152ndash161 2016

[18] J Li B B Yang Y H Lu L Xin Z H Wang and T Shojildquoe degradation mechanism of inconel 690TT induced byfretting wear in airrdquo Tribology International vol 116pp 147ndash154 2017

[19] G Xianglong L Ping T Lichen et al ldquoEffects of slidingamplitude and normal load on the fretting wear behavior ofalloy 690 tube exposed to high temperature waterrdquo TribologyInternational vol 116 pp 155ndash163 2017

[20] Special Metals INCONEL alloy X-750 Data Sheet 2004Publication No SMC-067 httpwwwspecialmetalscom

[21] C Marsh S Depinoy and D Kaoumi ldquoEffect of heattreatment on the temperature dependence of the fracturebehavior of X-750 alloyrdquo Materials Science and EngineeringA vol 677 pp 474ndash484 2016

[22] D Wenbo S Yanhua D Chunhua and Y Lie ldquoStructuralstiffness of X-750 alloy bump foil strips for compliant foilbearings with different heat treatmentsrdquo Journal of Tribologyvol 138 no 3 article 031702 2016

[23] G X Chen and Z R Zhou ldquoStudy on transition betweenfretting and reciprocating sliding wearrdquo Wear vol 250no 1ndash12 pp 665ndash672 2001

[24] J F Archard ldquoContact and rubbing of flat surfacesrdquo Journal ofApplied Physics vol 24 no 8 pp 981ndash988 1953

[25] S C Lim M F Ashby and J H Brunton ldquoWear-ratetransitions and their relationship to wear mechanismsrdquoActa Metallurgica vol 35 no 6 pp 1343ndash1348 1987

[26] S C Lim ldquoRecent developments in wear-mechanism mapsrdquoTribology International vol 31 no 1ndash3 pp 87ndash97 1998

[27] X LongW Zihao L Jie Y Lu and T Shoji ldquoMicrostructuralcharacterization of subsurface caused by fretting wear ofinconel 690TT alloyrdquo Material Characteristics vol 115pp 32ndash38 2016

[28] R Rybiak S Fouvry and B Bonnet ldquoFretting wear of stainlesssteels under variable temperature conditions introduction ofa ldquocompositerdquo wear lawrdquoWear vol 268 no 3-4 pp 413ndash4232010

[29] J F Zheng J Luo J L Mo J F Peng X S Jin andMH ZhuldquoFretting wear behaviors of a railway axle steelrdquo TribologyInternational vol 43 no 5-6 pp 906ndash911 2010

[30] K V Virendra N Hamza S S R Ganesh H MurthyA N Majila and D C Fernando ldquoEffect of contact pressureand stress ratio on the fretting fatigue behaviour of Ti-6Al-4Vrdquo Material Science and Engineering A vol 707 pp 647ndash656 2017

[31] J J Madge S B Leen and P H Shipway ldquoe critical role offretting wear in the analysis of fretting fatiguerdquoWear vol 263no 1ndash6 pp 542ndash551 2007

14 Advances in Materials Science and Engineering

during PSR was always lower with no apparent fluctuationduring the steady-stage level due to the minimum tangentialforce between the contact interfaces where the central zoneswere mechanically interlocked In this case the highernormal load triggers the traction coefficient where thecritical total sliding shear force is always higher than thetangential force [5 11] However in GSR the highest peak offriction occurred prior to the fluctuating steady-stage levelmainly due to the strong plastic deformation of work-hardened layer of the contacting surfaces [23 29] On theother hand the fluctuations in COF are attributed to themodifications in the contact interface which are linked to thethird-body rheology ie wear debris formation and itsentrapment and ejection from the contact zone [27]

e fretting loops generated by Ft-D curves in Figure 9are good indicators to show the slip condition at any mo-ment e area enclosed by the curves is the measure ofdissipated energy produced by friction [10 30] e frictionwork performed provides a more representative explanationof the surface damage Usually it has been noticed that thewear volume V is proportional to the energy dissipated Edin the contact and described as V αtimes 1113936Ed where α is thefriction energy wear coefficient [6] e degree of slope Sccan be considered as wear characteristics of the slidingconditions and materials Besides the unified slip indexapproach also offers the knowledge of fretting conditionsand considered as an appropriate means for estimatingfretting wear problems In accordance with the terms of slipindex when the slip ratio s⟶ 0 the contacts are in stickand as the slip ratio approaches to 1 partial slip and thengross slip prevail [2] e partial slip contacts in smalldisplacements induce cyclic stresses which favor cracknucleation and propagation but the loading condition isnondissipative with limited surface damage at the peripheryas shown in Figure 10 However the friction dissipation inGSR correlated with the plastic flow delamination andoxidation wear mechanisms causes a large amount ofsurface damage by extending the contact area and reducingthe contact pressure profile (Figure 11)

e main damage mechanisms ie cracking (frettinginduced by fatigue) and material loss (fretting induced bywear) are often appear as a competing process which wasextensively explored during the last decade [1 3 5 6 31ndash34]For instance the material loss during GSR can eliminatesmall cracks or fill up the opening of a deep crack andaccommodate the main portion of the imposed displace-ment as a consequence it strongly reduces the slip am-plitude and then the debris formation In fact the debrisejection has great impact on the third-body establishment ifit is trapped between the contacts the degradation processcan be suppressed and the most of the velocity differencebetween the friction pairs would be completely accommo-dated in a dissipative manner by the powder bed [33 34] Asfor cracking the effects of frictional force and the contactload are huge on the crack initiation and growth duringfretting fatigue where the frictional force triggers the crackinitiation while the contact load disrupts the crack growthduring the propagation period [37] Meanwhile it is re-ported that the cracks on the worn scar surface nucleated

and propagated along the direction of 30ndash50deg to the surfaceinterior which was in the range of calculated maximumshear stress angle [18]

SEM morphology in Figure 12(a) shows the interestingwear phenomenon where the thick layer of Inconel X-750alloy was stuck to the worn surface of the oscillating ball dueto the adhesive microslip In return with the further frettingthe material transferred to the surface of GCr14 ball has thehighest possibility to transfer back to the previous wornsurface of Inconel X-750 alloy [8] Besides the transferredwear layer was highly oxidized compared to the stick and slipregions of the steel ball as shown in Figure 13 e debrisdetached from the contact pairs is essentially composed ofnonmagnetic single component oxides eg Fe2O3 NiO andCr2O3 or more complex oxides eg NiCr2O4 and NiFe2O4[38] However the oxidization process was rapid on theworn surface of the steel ball during GSR which is because ofmore mechanical energy being converted to the thermalheat and it is believed that the frictional heat during GSRwas higher than in PSR [19]

5 Conclusion

e main purpose of this study was to explore the degra-dation evolutions of Inconel X-750 co-acted with GCr15steel ball through the dry fretting tests and observationsanalyses by using 3D surface profiler SEM and EDXAccording to the results the conclusions can be drawn asfollows

(i) e degradation mechanisms of Inconel X-750 weretotally dependent on the fretting regimes and variedwith the fretting time

(ii) e wear volume and wear depth were very low inPSR and wear mechanisms were associated with thedeformations adhesion and fatigue crack emicrocracks were present around the stick domainin 3times104 cycle and the radial cracks fully coveredthe contact center above 105 cycle along with thebigger crack in the contact border e large layer ofductile X-750 alloy was transferred to the wearsurface of the steel ball due to the exhaustion byhighly concentrated cyclic loading during the laterstages of fretting

(iii) In GSR the degradation mechanisms were as fol-lows (1) adhesive wear (galling and scuffing) (2)abrasive wear by third-body particle which is amechanical removal process (3) delaminationwhich is influenced by the material fatigue in theshallow subsurface layer and (4) oxidation of debrisparticles and surface layer due to the higher fric-tional heat which can enhance the load-carryingcapacity as well as reduce the wear rate in the laterstages of fretting process

(iv) e dependence of fretting time was negligibleduring PSR in respect of wear properties such aswear volume scar area and depth However it has agreat impact to evolve the degradation mechanisms

Advances in Materials Science and Engineering 13

from asperity deformation to the crack initiationand propagation which is a critical damage duringPSR On the other hand the wear volume and scararea were increased significantly by time duringGSR but the degradation evolutions were combinedand repeated with the mentioned wear mechanismsin a whole fretting process

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

e first author would like to acknowledge the scholarshipsupport from China Scholarship Council (CSC) is workwas supported by the Aeronautical Science Fund of China(Grant no 20164058002) National Natural Science Foun-dation of China (Grant No51735006) and Tsinghua Uni-versity Initiative Scientific Research Program

References

[1] R B Waterhouse ldquoFretting wearrdquo Wear vol 100 no 1ndash3pp 107ndash118 1984

[2] M Varenberg I Etsion and G Halperin ldquoSlip index a newunified approach to frettingrdquo Tribology Letters vol 17 no 3pp 569ndash573 2004

[3] O Vingsbo and S Soderberg ldquoOn fretting mapsrdquo Wearvol 126 no 2 pp 131ndash147 1988

[4] R D Mindlin and H Deresiewiez ldquoElastic spheres in contactunder varying oblique forcesrdquo Journal of Applied Mechanicsvol 20 pp 327ndash344 1953

[5] Z R Zhou and L Vincent ldquoMixed fretting regimerdquo Wearvol 181ndash183 pp 531ndash536 1995

[6] S Fouvry P Kapsa and L Vincent ldquoQuantification offretting damagerdquo Wear vol 200 no 1-2 pp 186ndash205 1996

[7] J Yu L Qian B Yu and Z Zhou ldquoNanofretting behavior ofmonocrystalline silicon (100) against SiO2 microsphere invacuumrdquo Tribology Letters vol 34 no 1 pp 31ndash40 2009

[8] H Mohrbacher J P Celis and J R Roos ldquoLaboratory testingof displacement and load induced frettingrdquo Tribology In-ternational vol 28 no 5 pp 269ndash278 1995

[9] Z R Zhou S Fayeulle and L Vincent ldquoCracking behaviourof various aluminium alloys during fretting wearrdquo Wearvol 155 no 2 pp 317ndash330 1992

[10] S Fouvry P Kapsa H Zahouani and L Vincent ldquoWearanalysis in fretting of hard coatings through a dissipatedenergy conceptrdquo Wear vol 203-204 pp 393ndash403 1997

[11] J Li and Y H Lu ldquoEffects of displacement amplitude onfretting wear behaviors and mechanism of Inconel 600 alloyrdquoWear vol 304 no 1-2 pp 223ndash230 2013

[12] G B Stachowiak and G W Stachowiak ldquoFretting wear andfriction behaviour of engineering ceramicsrdquo Wear vol 190no 2 pp 212ndash218 1995

[13] B Bhushan and B K Gupta Handbook of Tribology Mate-rials Coatings and Surface Treatments McGraw-Hill NewYork NY USA 1991

[14] H Y Zhang Y H Lu M Ma and J Li ldquoEffect of precipitatedcarbides on the fretting wear behavior of Inconel 600 alloyrdquoWear vol 315 no 1-2 pp 58ndash67 2014

[15] X Mi W X Wang X M Xiong et al ldquoInvestigation offretting wear behavior of Inconel 690 alloy in tubeplatecontact configurationrdquoWear vol 328-329 pp 582ndash590 2015

[16] L Jie L Yonghao Z Haoyang and L Xin ldquoEffect of grain sizeand hardness on fretting wear behavior of inconel 600 alloysrdquoTribology International vol 81 pp 215ndash222 2015

[17] L Xin B B Yang Z H Wang J Li Y H Lu and T ShojildquoMicrostructural evolution of subsurface on inconel 690TTalloy subjected to fretting wear at elevated temperaturerdquoMaterials amp Design vol 104 pp 152ndash161 2016

[18] J Li B B Yang Y H Lu L Xin Z H Wang and T Shojildquoe degradation mechanism of inconel 690TT induced byfretting wear in airrdquo Tribology International vol 116pp 147ndash154 2017

[19] G Xianglong L Ping T Lichen et al ldquoEffects of slidingamplitude and normal load on the fretting wear behavior ofalloy 690 tube exposed to high temperature waterrdquo TribologyInternational vol 116 pp 155ndash163 2017

[20] Special Metals INCONEL alloy X-750 Data Sheet 2004Publication No SMC-067 httpwwwspecialmetalscom

[21] C Marsh S Depinoy and D Kaoumi ldquoEffect of heattreatment on the temperature dependence of the fracturebehavior of X-750 alloyrdquo Materials Science and EngineeringA vol 677 pp 474ndash484 2016

[22] D Wenbo S Yanhua D Chunhua and Y Lie ldquoStructuralstiffness of X-750 alloy bump foil strips for compliant foilbearings with different heat treatmentsrdquo Journal of Tribologyvol 138 no 3 article 031702 2016

[23] G X Chen and Z R Zhou ldquoStudy on transition betweenfretting and reciprocating sliding wearrdquo Wear vol 250no 1ndash12 pp 665ndash672 2001

[24] J F Archard ldquoContact and rubbing of flat surfacesrdquo Journal ofApplied Physics vol 24 no 8 pp 981ndash988 1953

[25] S C Lim M F Ashby and J H Brunton ldquoWear-ratetransitions and their relationship to wear mechanismsrdquoActa Metallurgica vol 35 no 6 pp 1343ndash1348 1987

[26] S C Lim ldquoRecent developments in wear-mechanism mapsrdquoTribology International vol 31 no 1ndash3 pp 87ndash97 1998

[27] X LongW Zihao L Jie Y Lu and T Shoji ldquoMicrostructuralcharacterization of subsurface caused by fretting wear ofinconel 690TT alloyrdquo Material Characteristics vol 115pp 32ndash38 2016

[28] R Rybiak S Fouvry and B Bonnet ldquoFretting wear of stainlesssteels under variable temperature conditions introduction ofa ldquocompositerdquo wear lawrdquoWear vol 268 no 3-4 pp 413ndash4232010

[29] J F Zheng J Luo J L Mo J F Peng X S Jin andMH ZhuldquoFretting wear behaviors of a railway axle steelrdquo TribologyInternational vol 43 no 5-6 pp 906ndash911 2010

[30] K V Virendra N Hamza S S R Ganesh H MurthyA N Majila and D C Fernando ldquoEffect of contact pressureand stress ratio on the fretting fatigue behaviour of Ti-6Al-4Vrdquo Material Science and Engineering A vol 707 pp 647ndash656 2017

[31] J J Madge S B Leen and P H Shipway ldquoe critical role offretting wear in the analysis of fretting fatiguerdquoWear vol 263no 1ndash6 pp 542ndash551 2007

14 Advances in Materials Science and Engineering

from asperity deformation to the crack initiationand propagation which is a critical damage duringPSR On the other hand the wear volume and scararea were increased significantly by time duringGSR but the degradation evolutions were combinedand repeated with the mentioned wear mechanismsin a whole fretting process

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

e first author would like to acknowledge the scholarshipsupport from China Scholarship Council (CSC) is workwas supported by the Aeronautical Science Fund of China(Grant no 20164058002) National Natural Science Foun-dation of China (Grant No51735006) and Tsinghua Uni-versity Initiative Scientific Research Program

References

[1] R B Waterhouse ldquoFretting wearrdquo Wear vol 100 no 1ndash3pp 107ndash118 1984

[2] M Varenberg I Etsion and G Halperin ldquoSlip index a newunified approach to frettingrdquo Tribology Letters vol 17 no 3pp 569ndash573 2004

[3] O Vingsbo and S Soderberg ldquoOn fretting mapsrdquo Wearvol 126 no 2 pp 131ndash147 1988

[4] R D Mindlin and H Deresiewiez ldquoElastic spheres in contactunder varying oblique forcesrdquo Journal of Applied Mechanicsvol 20 pp 327ndash344 1953

[5] Z R Zhou and L Vincent ldquoMixed fretting regimerdquo Wearvol 181ndash183 pp 531ndash536 1995

[6] S Fouvry P Kapsa and L Vincent ldquoQuantification offretting damagerdquo Wear vol 200 no 1-2 pp 186ndash205 1996

[7] J Yu L Qian B Yu and Z Zhou ldquoNanofretting behavior ofmonocrystalline silicon (100) against SiO2 microsphere invacuumrdquo Tribology Letters vol 34 no 1 pp 31ndash40 2009

[8] H Mohrbacher J P Celis and J R Roos ldquoLaboratory testingof displacement and load induced frettingrdquo Tribology In-ternational vol 28 no 5 pp 269ndash278 1995

[9] Z R Zhou S Fayeulle and L Vincent ldquoCracking behaviourof various aluminium alloys during fretting wearrdquo Wearvol 155 no 2 pp 317ndash330 1992

[10] S Fouvry P Kapsa H Zahouani and L Vincent ldquoWearanalysis in fretting of hard coatings through a dissipatedenergy conceptrdquo Wear vol 203-204 pp 393ndash403 1997

[11] J Li and Y H Lu ldquoEffects of displacement amplitude onfretting wear behaviors and mechanism of Inconel 600 alloyrdquoWear vol 304 no 1-2 pp 223ndash230 2013

[12] G B Stachowiak and G W Stachowiak ldquoFretting wear andfriction behaviour of engineering ceramicsrdquo Wear vol 190no 2 pp 212ndash218 1995

[13] B Bhushan and B K Gupta Handbook of Tribology Mate-rials Coatings and Surface Treatments McGraw-Hill NewYork NY USA 1991

[14] H Y Zhang Y H Lu M Ma and J Li ldquoEffect of precipitatedcarbides on the fretting wear behavior of Inconel 600 alloyrdquoWear vol 315 no 1-2 pp 58ndash67 2014

[15] X Mi W X Wang X M Xiong et al ldquoInvestigation offretting wear behavior of Inconel 690 alloy in tubeplatecontact configurationrdquoWear vol 328-329 pp 582ndash590 2015

[16] L Jie L Yonghao Z Haoyang and L Xin ldquoEffect of grain sizeand hardness on fretting wear behavior of inconel 600 alloysrdquoTribology International vol 81 pp 215ndash222 2015

[17] L Xin B B Yang Z H Wang J Li Y H Lu and T ShojildquoMicrostructural evolution of subsurface on inconel 690TTalloy subjected to fretting wear at elevated temperaturerdquoMaterials amp Design vol 104 pp 152ndash161 2016

[18] J Li B B Yang Y H Lu L Xin Z H Wang and T Shojildquoe degradation mechanism of inconel 690TT induced byfretting wear in airrdquo Tribology International vol 116pp 147ndash154 2017

[19] G Xianglong L Ping T Lichen et al ldquoEffects of slidingamplitude and normal load on the fretting wear behavior ofalloy 690 tube exposed to high temperature waterrdquo TribologyInternational vol 116 pp 155ndash163 2017

[20] Special Metals INCONEL alloy X-750 Data Sheet 2004Publication No SMC-067 httpwwwspecialmetalscom

[21] C Marsh S Depinoy and D Kaoumi ldquoEffect of heattreatment on the temperature dependence of the fracturebehavior of X-750 alloyrdquo Materials Science and EngineeringA vol 677 pp 474ndash484 2016

[22] D Wenbo S Yanhua D Chunhua and Y Lie ldquoStructuralstiffness of X-750 alloy bump foil strips for compliant foilbearings with different heat treatmentsrdquo Journal of Tribologyvol 138 no 3 article 031702 2016

[23] G X Chen and Z R Zhou ldquoStudy on transition betweenfretting and reciprocating sliding wearrdquo Wear vol 250no 1ndash12 pp 665ndash672 2001

[24] J F Archard ldquoContact and rubbing of flat surfacesrdquo Journal ofApplied Physics vol 24 no 8 pp 981ndash988 1953

[25] S C Lim M F Ashby and J H Brunton ldquoWear-ratetransitions and their relationship to wear mechanismsrdquoActa Metallurgica vol 35 no 6 pp 1343ndash1348 1987

[26] S C Lim ldquoRecent developments in wear-mechanism mapsrdquoTribology International vol 31 no 1ndash3 pp 87ndash97 1998

[27] X LongW Zihao L Jie Y Lu and T Shoji ldquoMicrostructuralcharacterization of subsurface caused by fretting wear ofinconel 690TT alloyrdquo Material Characteristics vol 115pp 32ndash38 2016

[28] R Rybiak S Fouvry and B Bonnet ldquoFretting wear of stainlesssteels under variable temperature conditions introduction ofa ldquocompositerdquo wear lawrdquoWear vol 268 no 3-4 pp 413ndash4232010

[29] J F Zheng J Luo J L Mo J F Peng X S Jin andMH ZhuldquoFretting wear behaviors of a railway axle steelrdquo TribologyInternational vol 43 no 5-6 pp 906ndash911 2010

[30] K V Virendra N Hamza S S R Ganesh H MurthyA N Majila and D C Fernando ldquoEffect of contact pressureand stress ratio on the fretting fatigue behaviour of Ti-6Al-4Vrdquo Material Science and Engineering A vol 707 pp 647ndash656 2017

[31] J J Madge S B Leen and P H Shipway ldquoe critical role offretting wear in the analysis of fretting fatiguerdquoWear vol 263no 1ndash6 pp 542ndash551 2007

14 Advances in Materials Science and Engineering

[32] P Arnaud S Fouvry and S Garcin ldquoWear rate impact on Ti-6Al-4V fretting crack risk experimental and numericalcomparison between cylinderplane and punchplane contactgeometriesrdquo Tribology International vol 108 pp 32ndash47 2017

[33] M H Zhu and Z R Zhou ldquoOn the mechanisms of variousfretting wear modesrdquo Tribology International vol 44 no 11pp 1378ndash1388 2011

[34] W S Gwidon Wear-Materials Mechanisms and PracticeJohn Wiley and Sons Ltd Hoboken NJ USA 2005

[35] M Godet and Y Berthier ldquoContinuity and dry friction anosborne reynolds approachrdquo Tribology Series vol 11pp 653ndash661 1987

[36] Y Berthier L Vincent and M Godet ldquoVelocity accommo-dation in frettingrdquo Wear vol 125 no 1-2 pp 25ndash38 1988

[37] F C Castro J A Araujo E N Mamiya and N Zouain ldquoAfatigue endurance criterion in two stages with application tofretting contactrdquo Tribology International vol 42 no 9pp 1297ndash1303 2009

[38] G C Wood and B Chattopadhyay ldquoTransient oxidation ofNi-base alloysrdquo Corrosion Science vol 10 no 7 pp 471ndash4801970

Advances in Materials Science and Engineering 15

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom