Abrasive wear resistance of the iron- and WC-based hardfaced coatings evaluated with scratch test method

7/27/2019 Abrasive wear resistance of the iron- and WC-based hardfaced coatings evaluated with scratch test method

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123

Vol.35,No.2(2013)123‐127

TribologyinIndustry

www.tribology.fink.rs

AbrasiveWearResistanceof theIron‐and

WC‐basedHardfacedCoatingsEvaluatedwith

ScratchTest MethodA.Vencla,B.Gligorijevićb,B.Katavićb,B.Nedićc,D.DžunićcaUniversity of Belgrade,Faculty of Mechanical Engineering,Belgrade,Serbia ,

bInstituteGoša,Belgrade,Serbia ,

cFaculty of Engineering,University of Kragujevac,Kragujevac,Serbia.

Keywords:

Abrasivewear

Scratchtest

Hhardfacing

Iron‐based and WC ‐based materials

SEM ‐EDS

ABSTRACT

Abrasivewear is one of themost common types of wear,whichmakes

abrasive wear resistance very important in many industries. Thehardfacing is considered as useful and economical way to improve the

performanceof componentssubmitted tosevereabrasivewear conditions,

withwide

range

of

applicable

filler

materials.

The

abrasive

wear

resistanceof the threedifferent hardfaced coatings (two iron‐based and

one WC ‐based), which were intended to be used for reparation of the

impact plates of the ventilation mill, was investigated and compared.

Abrasivewear testswerecarried ‐out by usingthescratchtester under the

dry conditions.Threenormal loadsof 10,50and 100N and theconstant

slidingspeed of 4mm/swereused.Scratchtest waschosenasarelatively

easy and quick test method.Wear mechanismanalysisshowed significant

infl uenceof thehardfaced coatingsstructure,which,alongwithhardness,hasdetermined coatingsabrasivewear resistance.

©2013PublishedbyFacultyofEngineering

Correspondingauthor:

A.Vencl

Tribology Laboratory,University of

Belgrade,Faculty of Mechanical

Engineering,KraljiceMarije16,11120Belgrade35,Serbia

E ‐mail:[email protected]

1. INTRODUCTION

More than 50 % of all wear‐related failures ofindustrial equipment are caused by abrasivewear [1]. The estimated costs of abrasive wearare between 1 and 4 % of the gross nationalproductofanindustrializednation[2].Forthesereasons,theabrasivewearresistanceisasubjectofgreatimportanceinmanyindustries,suchasagriculture,mining,mineralprocessingetc.

Hardfacing could be defined as “coatingdeposition process in which a wear resistant,

usually harder, material is deposited on thesurfaceofa componentbysomeof the weldingtechniques”.Inmostcases,hardfacingisusedforcontrolling abrasive and erosive wear, like inmining, crushing and grinding, and agricultureindustries(buckets,bucketteeth,millhammers,ball mills, digging tools, conveyer screws, etc.[3,4]). Hardfacing is also used to controlcombinations of wear and corrosion, asencounteredbymudseals,plows,knivesinthe

food processing industry, pumps handlingcorrosiveliquids,orslurries[5].Thehardfacingisconsideredaseconomicalwaytoimprovethe

R

E S E A R C H



A.Vencl at al.,Tribology inIndustry Vol.35,No. 2(2013)123‐127

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performanceofcomponentssubmittedtoseverewear conditions, with wide range of applicablefillermaterials[6,7].Theiron‐basedfillermaterialshavedrawnmuch

attention due to their low cost and goodresistance to abrasion in the hardfacedcondition. However, their use is limited inapplications where high impact loading ispresent,i.e.high‐stressorgougingabrasion[8].Forthisreason,effortsarebeingmadetowardsthe improvement of their impact and otherproperties[9].Theprogressisachievedmostlyby modifying the hardfaced coating’s structure.Taking into account their low price andimprovedproperties,theresistancetoabrasivewear of the iron‐based hardfaced coatings is

normallytestedagainsttheresistanceofproven,butmoreexpensivematerials,suchasWC‐basedhardfacedcoatings.Abrasive wear has been defined as “wear bydisplacement of material from surfaces inrelativemotioncaused bythe presenceof hardparticles either between the surfaces orembeddedinoneofthem,orbythepresenceofhard protuberances on one or both of thesurfaces”[10].Thesecondpartofthisdefinition

corresponds to puretwo‐body abrasion,wheretested material slides against harder androugher counter face material, while the firstpart corresponds to the three‐ and two‐bodyabrasion, respectively. Another interestingexample of two‐body abrasion is the abrasiveerosion, which is the special case of erosivewear. Abrasive erosion has been defined as“erosivewearinwhichthelossofmaterialfromasolidsurfaceisduetorelativemotionofsolidparticleswhichareentrainedinafluid,moving

nearly parallel to a solid surface” [10]. Scratchtest offers a possibility for comparison ofdifferent materials relatively easy and in shortperiodoftime,withgoodreproducibility[11].Insingle‐pass scratch test a stylus (which tip ismade of hard material) slide over the testsampleproducingasinglescratch,whichseemsto be appropriate simulation of the two‐bodyabrasion.Inthisstudy,theabrasivewearresistanceofthethree different hardfaced coatings (two iron‐basedandoneWC‐based)wasinvestigatedandcompared.

2. EXPERIMENTALDETAILS

2.1 Materials

The filler materials (coating materials) weremanufacturedbyCastolinEutecticCo.Ltd,Vienna.Their nominal chemical composition is shown inTable 1. The iron‐based filler materials (basiccoveredelectrodes) were depositedbyusing theshieldedmetalarcwelding(SMAW)process.TheWC‐basedfillermaterialwasdepositedbyoxy‐fuelgas welding (OFW) process. The substratematerialwasthehot‐rolledS355J2G3steel.Table1.Coatingscomposition,processandhardness.

CoatingNominalchemical

compositionHardfacing

processHardness

HV5

4541 Fe‐Cr‐C‐Si SMAW 7395006 Fe‐Cr‐C‐Si SMAW 781

7888T WC‐Ni‐Cr‐Si‐B OFW 677

All coatings were deposited by hardfacing in asingle pass (one layer). The substratepreparation and hardfacing procedures(deposition parameters) are describedelsewhere [9,12]. The measurements of near‐surface hardness are performed on the cross‐section of hardfaced samples by Vickers

indenter(HV5),andpresentedin(Table1).The samples for structure characterization areobtained by cutting the hardfaced materialsperpendicular to coatings surface. The obtainedcross‐sectionsaregroundwithSiCabrasivepapersdown to P1200 and polished with aluminasuspensions downto1μm.The polishedsurfacesare analyzed by using the scanning electronmicroscope(SEM)equippedwithenergydispersivesystem (EDS). The SEM‐EDS analysis wasperformed at University of Belgrade, Faculty of

MiningandGeologybyusingtheJEOLJSM–6610LVSEM connected with the INCA350 energydispersion X‐ray analysis unit. The electronacceleration voltage of 20 kV and the tungstenfilament were used. Before SEM‐EDSanalysis wasperformed, polished surfaces were 20 nm goldcoated in a vacuum chamber by use of a sputtercoaterdevice.TheFig.1ashowsthenear‐surfacestructureofthe4541 iron‐based hardfaced coating. The primaryaustenite phase occupies more than a half ofvolume (50.7vol.%) andthe restis the lamellareutectic mixture ofausteniteandCr‐carbides [9].




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Fig.1.Thestructures(SEM)of:(a)4541,(b)5006and(c)7888Thardfacedcoating;back‐scatteredelectronimages.The5006materialduringsolidificationachievesnear‐eutectic structure (Fig. 1b). A smallsphericalprimaryCr‐carbidesareobserved(9.1vol.%)intheeutecticmatrix.Basedonelectronmicroprobeanalysis(EMPA),bothcoatings4541and 5006 contain (Cr,Fe)7C3 primary andeutecticcarbides. The Figure 1cshowsa largerWCgrains(60vol.%),whichareembeddedintheNi‐Crbasedmatrix.2.2 Scratchabrasiontesting

Abrasive wear tests are carried out on thescratch tester under the dry conditions, inambient air at room temperature (≈ 25 °C). AschematicdiagramofscratchtestingispresentedinFigure 2.Stylus (indenter) was pressed with

selectednormalload(10,50and100N)againstsurface of the test sample and moved withconstantspeed(4mm/s),producingthescratchofcertainwidthandlength(10mm)onthetestsample. Indenter had Rockwell shape and theconewasdiamondwithradiusof0.2mm.

Fig.2.Schematicdiagramofscratchtesting.Onsurfaceofeachmaterialunderinvestigationat least three scratches are made with a gapbetweenscratchesof atleast1 mm.Before andafter testing, both the indenter and the testsamples are degreased and cleaned withbenzene.ThewearscarwidthsonthesurfaceofthetestsamplesaremeasuredfromSEMimagesattheendoftesting.Thewearscarwidthsandthe known indenter geometry are used to

calculate the volume loss. After testing, themorphologyofthetestsampleswornsurfacesisexaminedwithSEM.3. RESULTS ANDDISCUSSION

The results of the wear tests are presented inFigures3,4and5.Takingintoaccountsignificantdifferences in structure homogeneity of thehardfaced coatings (Fig. 1), the repeatability ofthe results, in terms of standard deviations, issatisfactory (within 16 %). Wear rate of thetestedmaterials(volumelossdividedbyscratchlength) increases with normal loading, asexpected.Thehighestwearexhibitscoating7888T. Nevertheless, wear rates for all coatings are

high,evenforabrasivewear.Thereasonforthisisprimarilyduetotheexperimentalconditions.Thetestconditionswerespecific,i.e.thespeedswere very low (4 mm/s) and the contactstressesveryhigh.Attheendoftest,thenormalstresses were between 2 and 5 GPa, whichdependsonthematerial,i.e.scratchwidthandapplied normal load. With these conditions, ahigh‐stress or even gouging abrasion can beexpected. With high‐stress abrasion, the worn

surface may exhibit varying degrees ofscratching with plastic flow of sufficientlyductile phases or fracture of brittle phases. Ingouging abrasion, the stresses are higher thanthose in high‐stress abrasion, and they areaccompaniedbylargeparticlesremovalfromthesurface,leavingdeepgrovesand/orpits[8].The relation between the wear rate and thehardnessoftestedhardfacedcoatingsisshowninFigure6.Thefirstfeatureisthattheabrasivewear rate decreases as the hardness increases,i.e.thehardestmaterial(coating5006)showedthehighestabrasivewearresistance.




126

Coating 4541(v = 4 mm/s)

0.75

1.88

0.10

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

3.2

10 50 100Normal load, N

W e

a r r a t e , m m

3 / m

Fig. 3. Wear rates of coating 4541 for differentnormalloads.

Coating 5006(v = 4 mm/s)

1.67

0.68

0.09

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

3.2


W e a r r a t e , m m

3 / m

Fig. 4. Wear rates of coating 5006 for differentnormalloads.

Coating 7888 T(v = 4 mm/s)

1.24

2.88

0.21

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

3.2


W e a r r a t e , m m

3 / m

Fig. 5. Wear rates of coating 7888 T for differentnormalloads.

0.10 0.09

1.24

0.750.68

1.67

0.21

1.88

2.88

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

670 690 710 730 750 770 790

Hardness HV5

W

e a r r a t e , m m

3 / m

10 N

50 N

100 N

Fig.6.Wearratevs.hardnessoftestedmaterialsfordifferentnormalloads.

For all applied loads, the relation betweenhardness and wear rate is non‐linear. It is morecurvedforhigherloads(Fig.6).Thisisconnectedwith the coatings structure and exhibited wearmechanism. Coatings 4541 and 5006 exhibitmainly ploughing abrasive wear (Fig. 7a), whilecoating7888Tdominanttypeofabrasivewearisfracture(cracking)abrasivewear(Fig.7b).

Fig.7.Thewearscarappearance(SEM)of:(a)4541and(b)7888Thardfacedcoating;50Nnormalload;

back‐scatteredelectronimages.




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4. CONCLUSION

Scratch test offers relatively easy and quickcomparisonofdifferentmaterialsonabrasivewear.Structureoftestedcoatingsshowedinfluenceonthe dominant type of abrasive wear, whichtogether with coatings hardness determinedcoatingsabrasivewearresistance.Coatings with lower hardness showed lowerabrasive wear resistance, but the dependence(hardnessvs.wearrate)wasnon‐linear.In the case of iron‐based coatings, dominanttypeofabrasivewearwasploughingandinthecase of WC‐based coatings, it was fracture

(cracking)abrasivewear. Acknowledgement

This work has been performed as a part ofactivities within the projects TR 34028, TR35021 and TR 35034. These projects aresupportedbytheRepublicofSerbia,MinistryofEducation, Science and TechnologicalDevelopment,whosefinancialhelpisgratefullyacknowledged.REFERENCES

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Abrasive wear resistance of the iron- and WC-based hardfaced coatings evaluated with scratch test method