Ostwald Ripening Process of Coherentdownloads.hindawi.com/journals/amse/2015/485626.pdf · Research Article Ostwald Ripening Process of Coherent Precipitates during Aging in Fe 0.75

Research ArticleOstwald Ripening Process of Coherent 1205731015840 Precipitates duringAging in Fe075Ni010Al015 and Fe074Ni010Al015Cr001 Alloys

N Cayetano-Castro M L Saucedo-Muntildeoz H J Dorantes-RosalesJorge L Gonzalez-Velazquez J D Villegas-Cardenas and V M Lopez-Hirata

Instituto Politecnico Nacional (ESIQIE-CNMN) Apartado Postal 118-556 07051 Mexico DF Mexico

Correspondence should be addressed to V M Lopez-Hirata vlopezhiprodigynetmx

Received 26 September 2014 Revised 16 December 2014 Accepted 6 January 2015

Academic Editor Jorg M K Wiezorek

Copyright copy 2015 N Cayetano-Castro et al This 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 is properlycited

The Ostwald ripening process was studied in Fe075

Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys after aging at 750 850 and 950∘Cfor different times The microstructural evolution shows a rounded cube morphology (Fe Ni)Al 1205731015840 precipitates aligned in theferrite matrix which changes to elongated plates after prolonged aging The variation of the equivalent radii of precipitates withtime follows the modified Lifshitz-Slyozov-Wagner theory for diffusion-controlled coarsening Thermo-Calc analysis shows thatthe chromium content is richer in the matrix than in the precipitates which causes higher hardness and coarsening resistance inthe aged Fe

074Ni010

Al015

Cr001

alloy

1 Introduction

The mechanical properties of precipitation hardened alloysare closely related to the morphology spatial distributionvolumetric fraction and average radius of the precipitatedparticles in the phase matrix These microstructural char-acteristics can be controlled by means of heat treatmentshowever they are also modified during the operation ofindustrial components at high temperatures for prolongedtimes The Ostwald ripening process is a metallurgical phe-nomenonwhich takes place at high temperatures and consistsof the dissolution of small precipitates and subsequent masstransfer to the larger precipitates during the heating ofalloys [1] The Lifshitz-Slyozov-Wagner (LSW) theory fordiffusion-controlled coarsening [2] predicts a coarseninggrowth kinetics with a time dependent on 11990513 consideringthe spherical precipitates without elastic interaction withthe phase matrix and volume fraction close to zero Thereare several modified LSW theories for diffusion-controlledcoarsening [3ndash6] which incorporated higher volume frac-tions and the precipitate morphology different from spheresas well as multicomponent alloys Nevertheless the temporalpower law of 11990513 is sustained in all of the above cases but the

time-independent precipitate size distribution of LSW theorybecomes broader and more symmetric with the increase involume fraction

The mechanical strength at high temperatures in Fe-Ni-Al alloys is mainly based on the presence of coherent(NiAl type) 1205731015840 precipitates with a B2 (CsCl) crystallinestructure dispersed in the ferritematrix [7]This intermetalliccompound precipitate is responsible for the precipitationhardening in different alloy systems such as PH stainlesssteels Nitralloy and Fe-Cr-Ni-Al based alloys [8] Thecoarsening resistance of these precipitates is an importantfactor to keep its mechanical strength at high temperaturesin these alloys One way for improving the coarseningresistance is by the addition of alloying elements to thesealloys in order either to decrease the lattice misfit whichmaintains the coherent interface between precipitate andmatrix or to delay the atomic diffusion process during thecoarsening process [9] The chromium addition is expectedto increase the high-temperature strength [10] in these ferriticalloys which may help to be used at higher temperatureswith a better performance against coarsening Thus it isessential to study the coarsening process of this type ofalloys

Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2015 Article ID 485626 7 pageshttpdxdoiorg1011552015485626

2 Advances in Materials Science and Engineering

Therefore the purpose of the present work is to carryout a comparative study of the coarsening process of theFe075

Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys after agingat temperatures of 750 850 and 950∘C for several times inorder to know the effect of the Cr addition on the growthkinetics of coarsening and mechanical properties of thisalloy

2 Experimental Details

Two alloy compositions Fe075

Ni010

Al015

and Fe074

Ni010

Al015

Cr001

were melted in an electric arc furnace under anargon atmosphere using high purity Fe (999) Ni (9999)Al (997) and Cr (999) The chemical composition ofalloys was verified pursuing the chemical analysis by theatomic absorption method with a GBS Avanta equipmentbased on a variation of ASTM E-353 standard [11] with anexperimental error between 004 and 026 depending onthe element The actual compositions were Fe-103atNi-152atAl and Fe-99atNi-154atAl-11atCr which arevery close to the nominal one The alloy ingots wereencapsulated in quartz tube under an argon atmosphereand heated at 1100∘C for one week in a tubular electricfurnace in order to destroy the as-cast microstructure andhomogenize the chemical composition Specimens of 30 times30 times 10mm were cut and encapsulated in a quartz tubeunder argon atmosphere to conduct the solution treatmentat 1100∘C for 1 h and then aged at 750 850 and 950∘Cfor times from 5 to 1000 h The solution treated and agedspecimens were preparedmetallographically and etched withan etchant composed of 2 vol- nitric acid in methanoland then observed with secondary electron image (SEI)in a JEM 6300 JEOL scanning electron microscope (SEM)equipped with an energy dispersive spectrometer (EDS) at25 kV The aged specimens of both alloys were also analyzedby X-ray diffraction analysis with Mo K120572 radiation with aSiemens D-5000 equipment in order to confirm the presenceof the ordered 1205731015840 phase The equivalent circus radius ofprecipitates 119903 was measured by means of the precipitate areaon SEM images with an image analyzing system In orderto get representative data 200 measurements were done indifferent zones of the specimensThesemeasurementsmainlycorresponded to precipitates with a cuboid morphology Thevolume fraction of precipitates was evaluated employing thearea method in both the alloy specimens aged at 750 850and 950∘C for 25 50 100 and 200 h STEM analysis of someaged specimens was carried out with the HAADF detectorto obtain a Z-contrast and it was combined with STEM-EDX analysis to know the distribution of chemical elementsin matrix and precipitates of some aged specimens TheVickers hardness HV 0112 s was measured in all the agedspecimens

3 Results and Discussion

31 Microstructural Evolution of Coarsening SEM micro-graphs of the precipitation evolution are shown in Figures1 and 2(a)ndash2(d) for the Fe

075Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys respectively aged at 750 and 950∘C for50 and 200 h Both figures show the presence of the 1205731015840precipitates in the ferritic matrix The 1205731015840 precipitates wereconfirmed to have the B2 (CsCl) crystalline structure asshown in Figure 3 which shows the superreflections for thisphase in bothX-ray diffractograms of the alloys aged at 950∘Cfor 50 h Several diffraction peaks of the 1205731015840 precipitates areoverlapped with those corresponding to the ferrite matrixThe morphology of the 1205731015840 precipitates is rounded cuboidsin both of the aged alloys from the early stages of agingat all temperatures (Figures 1 and 2(a)) The straight sidesof precipitates suggest the presence of a coherent interfacebetween precipitates and matrix The precipitates becomealigned with the ferritic matrix over the course of time(Figures 1 and 2(b)) This alignment has been reported [12]to occur in the lt100gt crystallographic direction of the ferritematrix since it corresponds to the softest one in the bcccrystalline structure This suggests that the alloy specimenshave the lt100gt orientation in the aged specimens A furtheraging promotes the increase in size of precipitates in both ofthe aged alloys The increase in precipitate size is higher asthe aging temperature increases Aging for longer times hasa tendency to form square or rectangular arrays of cuboidprecipitates in both alloys however this fact seems to behigher in the Fe

075Ni010

Al015

alloy aged at 750 and 850∘Cthan that in the other one (Figures 1 and 2(b)) At agingat 950∘C elongated arrays of precipitates are aligned withrespect to the ferriticmatrix in both alloys (Figures 1 and 2(c)-2(d)) Some coalescence of precipitates is observed in thesearrays and the straight sides of some precipitates becomecurved This suggests the loss of coherency between theprecipitates and matrix This characteristic is more noto-rious in the case of the aged Fe

075Ni010

Al015

alloy Thisbehavior seems to be related to a higher elastic-strain effectin this alloy [13] No splitting of precipitates was observedto occur in both the aged alloys The volume fraction ofprecipitates is also indicated in Figures 1 and 2 and this isin general higher for the alloy without chromium howeverthe volume fractions are very close in both alloys aged at750∘C

32 Coarsening Growth Kinetics The average equivalentcircus radius 119903 of 1205731015840 precipitates expressed as 1199033 is plottedas a function of aging time in Figure 4 for the aged Fe

075

Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys This figureshows straight line curves for the different cases which sug-gest that the LSW theory for diffusion-controlled coarseningis followed in this study The LSW theory and modified LSWtheories [1 2] express mathematically the variation of particleradius with time as follows

1199033minus 1199033

119900= 119896119903119905 (1)

where 119903119900and r are the average radius of precipitates at the

onset of coarsening and time 119905 respectively and 119896119903is a

rate constant which can be determined from the slope ofstraight lines in Figure 4 The most adequate value of thetime exponent 119899 was determined using a regression analysisfor each alloy and aging temperature This indicated that

Advances in Materials Science and Engineering 3

f = 032

(a)

f = 022

(b)

f = 034

(c)

f = 032

2120583m

(d)

Figure 1 SEM micrographs of the Fe075

Ni010

Al015

alloy aged at (a-b) 750 and (c-d) 950∘C for 50 and 200 h respectively

f = 031

(a)

f = 019

(b)

f = 032

(c)

f = 023

2120583m

(d)

Figure 2 SEMmicrographs of the Fe074

Ni010

Al015

Cr001



120573998400

Ferrite

Inte

nsity

2120579 (deg)15 20 25 30 35 40 45 50

Fe074Ni010Al015Cr001 alloy aged at 950∘C for 50h

Fe075Ni010Al015 alloy aged at 950∘C for 50h

Figure 3 XRD diffractograms of the Fe075

Ni010

Al015

andFe074

Ni010

Al015

Cr001

alloys aged at 950∘C for 50 h

r3(n

m3times10

7)

10

8

6

4

2

0

0 200 400 600 800

Aging time (h)

k1023 K = 107 times 104 nm3hk1123 K = 118 times 105 nm3hk1223 K = 443 times 105 nm3h


Fe074Ni010Al015Cr001

Fe075Ni010Al015

Figure 4 Plot of 1199033 value for precipitates against aging time for theaged Fe

075Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys

the adjusted contribution ratio 1198772 was between 0964 and0993 0940 and 0992 and 0930 and 0935 for 119899 = 3 25and 2 respectively in the ternary alloy On the other handthis value was between 0985 and 0995 0984 and 0991and 0945 and 0990 for 119899 = 3 25 and 2 respectively inthe quaternary alloy Thus the highest adjusted contributionratio 1198772 corresponded to the exponent 119899 equal to 3 which is

in agreement with the modified LSW theory for diffusion-controlled coarsening

Figure 4 also shows the values of rate 119896 constant foreach case and they indicate that the coarsening process takesplace more rapidly for the Fe

075Ni010

Al015

alloy aged atthe three temperatures than that of the alloy with the Craddition in spite of the lower volume fraction of precipitationAdditionally the activation energy for the coarsening processwas determined to be 194 and 212 kJmolminus1 for the ternary andquaternary alloys respectively using the Arrhenius plot ofthe rate constant 119896 The activation energy of the quaternaryalloy is higher than that of the ternary alloy which is in agree-mentwith the slower coarsening kinetics observed in the agedFe074

Ni010

Al015

Cr001

alloy Both values of energy are closeto the activation energy of 188ndash234 kJmolminus1 reported for theinterdiffusion process in Fe-Al alloys [14]

This behavior suggests the effect of chromium on theOstwald ripening process in this alloy Figure 5(a) illustratesthe HAADF-STEM image of the Fe

074Ni010

Al015

Cr001

alloyaged at 950∘C for 50 h Some 1205731015840 precipitates and the ferritematrix can be observed in the micrograph The STEM inten-sity profiles corresponding to Fe Ni Al and Cr elementsfollowing the line from A to B indicated in Figure 5(a) areshown in Figure 5(b) The presence of chromium is slightlyhigher in the ferrite matrix than that observed in the 1205731015840precipitates The iron content of precipitates is higher thanthat of nickel and aluminum In order to show more clearlythe effect of alloying elements a thermo-Calc equilibriumanalysis [15] was carried out for the two alloy compositions attemperatures between 750 and 950∘C Thermo-Calc analysisindicates that the ferrite matrix is richer in chromium about11 at for all temperatures in comparison with that in the 1205731015840precipitates This detail is in good agreement with the chem-ical behavior reported in the literature for Fe-Ni-Al-Cr alloys[16] The thermo-Calc calculated mole fraction of alloyingelements is shown in Figure 6 for the equilibrium 1205731015840 phasefor the Fe

075Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys attemperatures between 750 and 950∘C These precipitates areexpected [17] to be an (Fe Ni)Al intermetallic compoundThermo-Calc analysis shows that the iron content in the1205731015840 precipitates increases with the aging temperature from

about 10 to 50 at while the nickel and aluminum contentsdecrease with temperature from about 45 to 20 at in bothalloys However the content of iron in the 1205731015840 precipitatesis slightly lower in the Fe

074Ni010

Al015

Cr001

alloy thanthat corresponding to the other alloy while the nickel andaluminum contents of the former alloy are slightly higherthan that of the latter alloy In the case of the alloy withchromium the chromium contents show a slight increasewith temperature from 004 to 022 at This chemicalbehavior suggests that the 1205731015840 precipitates are an intermetalliccompound closer to the NiAl compound in both alloys agedat 750∘C since the Fe content is low In contrast the 1205731015840precipitates are a compound of (Fe Ni)Al type in both alloysaged at 850 and 950∘C showing a considerable amount ofiron which is in good agreement with Figure 5This behaviormay be favorable for having a higher coarsening resistance inthese precipitates since the atomic diffusion process would


A

B

2120583m CNMN-IPN ARM 200CF

(a)

FeNi

AlCr

1000

800

600

400

200

0

00 01 02 03 04 05 06

Inte

nsity

pro

file (

au)

Length (120583m)

(b)

Figure 5 (a) HAADF-STEM image of (Fe Ni)Al precipitates in a Fe matrix and (b) intensity profile of Fe Ni Al and Cr elements

05

04

03

02

01

00

750 800 850 900 950

FeAlNi

Cr

(Fe Ni)Al precipitates

Mol

e fra

ctio

n

Temperature (∘C)

Fe074Ni010Al015Cr001Fe075Ni010Al015

Figure 6 Calculated fraction mole of alloying elements in the 1205731015840 precipitates against aging temperature for the Fe075

Ni010

Al015

andFe074

Ni010

Al015

Cr001

alloys

be more complex which may cause its retardation [2] Asmentioned above the coarsening resistance in the alloywith chromium is higher than that observed in the otheralloy This fact can be attributed mainly to the presence ofchromium in both the ferritematrix and1205731015840 precipitateswhichcause a slower diffusion process during the coarsening ofprecipitates

The precipitate size distribution plot of the probabilitydensity versus the normalized radius 120588 is shown in Figures7(a)ndash7(d) for the Fe

075Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys respectively aged at 750∘C for 50 and at 950∘C for150 h The size distribution of the LSW theory for diffusion-controlled coarsening is also shown in these figures The sizedistribution of both alloys aged at 750∘C for 50 h (Figures


00 02 04 06 08 10 12 14 16 18 20 22

25

20

15

10

05

00

LSW

Prob

abili

ty d

ensit

y

120588

FeNiAl750∘C-50h

(a)

LSW

25

20

15

10

05

00

00 02 04 06 08 10 12 14 16 18 20 22

120588

FeNiAl950∘C-150h

Prob

abili

ty d

ensit

y

(b)

LSW

25

20

15

10

05

00

00 02 04 06 08 10 12 14 16 18 20 22

120588

750∘C-50hFeNiAlCr

Prob

abili

ty d

ensit

y

(c)

LSW

25

20

15

10

05

00

120588

00 02 04 06 08 10 12 14 16 18 20 22

950∘C-150hFeNiAlCr

Prob

abili

ty d

ensit

y

(d)

Figure 7 Distribution of precipitate size for the (a-b) Fe075

Ni010

Al015

and (c-d) Fe074

Ni010

Al015

Cr001

alloys aged at 750∘C for 50 h and 950∘Cfor 150 h respectively

7(a) and 7(c)) is more symmetrical and closer to that one ofLSW theory In contrast the size distribution of both alloysaged at 950∘C for 150 h (Figures 7(b) and 7(d)) is broaderand more symmetrical which is a coarsening characteristicobserved in different binary and ternary alloys either withlarge volume fraction of precipitates or with high coherency-elastic strain effect [1 2]

33 Aging Curves The aging curves are shown in Figure 8for the two alloys aged at 750 850 and 950∘C The hardnessof Fe074

Ni010

Al015

Cr001

alloy is higher than that of theFe075

Ni010

Al015

alloy in spite of the lower volume fractionof precipitates This higher hardness can be related to thepresence of a small amount of chromium in the matrix andprecipitates (Figure 6) Besides the increase in Fe content forthe 1205731015840 precipitates has been reported [18] to cause an increasein strength while its decrease tends to improve its ductility

The highest resistance to the overaging in these alloys occursduring the aging at 750∘Cwhich shows the slowest coarseningkinetics in both alloys In contrast the lowest coarsen-ing resistance was observed to take place in the highestaging temperature because of the fastest Ostwald ripeningprocess

4 Conclusions

The presence of chromium in the Fe075

Ni010

Al015

alloypromotes a higher coarsening resistance of the 1205731015840 precipitatesduring aging at temperatures of 750 850 and 950∘C aswell asa higher response to the precipitation hardeningThese char-acteristics can be related to the presence of chromium in boththe ferrite matrix and 1205731015840 precipitatesThe chromium additionseems to promote a delay of the precipitate coarsening and anincrease in the solution strengthening


0 100 200 300 400 500 600 700 800 900 1000

520

510

500

490

480

470

460

450

440

Aging time (h)

750∘C 850∘C

950∘C




Vick

ers h

ardn

ess

HV

01

12

s

Figure 8 Aging curves for the Fe075

Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors wish to acknowledge the financial support fromSIP-IPN and Conacyt

References

[1] A Baldan ldquoProgress in Ostwald ripening theories and theirapplications to nickel-base superalloysrdquo Journal of MaterialsScience vol 37 no 11 pp 2171ndash2202 2002

[2] G Kostorz Phase Transformations in Materials Wiley-VCHWeinheim Germany 2nd edition 2001

[3] C J Kuehmann and P W Voorhees ldquoOstwald ripening internary alloysrdquo Metallurgical and Materials Transactions APhysicalMetallurgy andMaterials Science vol 27 no 4 pp 937ndash942 1996

[4] N Cayetano-Castro H J Dorantes-Rosales V M Lopez-Hirata J J Cruz-Rivera J Moreno-Palmerin and J LGonzalez-Velazquez ldquoCoarsening kinetics of coherent precip-itates in Fe-10 Ni-15 Al alloyrdquo Revista de Metalurgia deMadrid vol 44 no 2 pp 162ndash169 2008

[5] K Thornton N Akaiwa and P W Voorhees ldquoLarge-scalesimulations of Ostwald ripening in elastically stressed solids IDevelopment of microstructurerdquo Acta Materialia vol 52 no 5pp 1365ndash1378 2004

[6] A J Ardell ldquoThe effect of volume fraction on particle coarsen-ing theoretical considerationsrdquoActaMetallurgica vol 20 no 1pp 61ndash71 1972

[7] M Schober C Lerchbacher E Eidenberger P Staron HClemens and H Leitner ldquoPrecipitation behavior of intermetal-licNiAl particles in Fe-6 atAl-4 atNi analyzed by SANS and3DAPrdquo Intermetallics vol 18 no 8 pp 1553ndash1559 2010

[8] G Sauthoff Intermetallics Wiley-VCH New York NY USA 1stedition 1995

[9] H J Rosales-Dorantes N Cayetano-Castro V M Lopez-Hirata M L Saucedo-Munoz D Villegas-Cardenas and FHernandez-Santiago ldquoCoarsening process of coherent 1205731015840 pre-cipitates in Fe-10wtNi-15wtAl and Fe-10wtNi-15wtAl-1wtCu alloysrdquo Materials Science and Technology vol 29 pp1492ndash1498 2013

[10] M A Munoz-Morris and D G Morris ldquoMicrostructure andmechanical behaviour of a Fe-Ni-Al alloyrdquoMaterials Science andEngineering A vol 444 no 1-2 pp 236ndash241 2007

[11] ASTM International ldquoStandard test methods for chemicalanalysis of stainless heat-resisting maraging and other similarchromium-nickel-iron alloysrdquo Tech Rep ASTM E-353 2006

[12] O Soriano-Vargas M L Saucedo-Munoz V M Lopez-Hirataand A M Paniagua-Mercado ldquoCoarsening of 1205731015840 precipitates inan isothermally-aged Fe

75-Ni10-Al15

alloyrdquo Materials Transac-tions vol 51 no 3 pp 442ndash446 2010

[13] A Baldan ldquoProgress in Ostwald ripening theories and theirapplications to the 1205741015840-precipitates in nickel-base superalloysPart II Nickel-base superalloysrdquo Journal of Materials Sciencevol 37 no 12 pp 2379ndash2405 2002

[14] H Mehrer Diffusion in Solid Metals and Alloys SpringerBerling UK 1st edition 1990

[15] Thermo-Cal software v 31Niv5TDB 2008[16] C Stallybrass and G Sauthoff ldquoFerritic Fe-Al-Ni-Cr alloys

with coherent precipitates for high-temperature applicationsrdquoMaterials Science and Engineering A vol 387ndash389 no 1-2 pp985ndash990 2004

[17] C Stallybrass A Schneider and G Sauthoff ldquoThe strengthen-ing effect of (NiFe)Al precipitates on themechanical propertiesat high temperatures of ferritic Fe-Al-Ni-Cr alloysrdquo Inter-metallics vol 13 no 12 pp 1263ndash1268 2005

[18] I M Anderson A J Duncan and J Bentley ldquoSite-distributionsof Fe alloying additions to B2-ordered NiAlrdquo Intermetallics vol7 no 9 pp 1017ndash1024 1999

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Nano

materials


Journal ofNanomaterials


Therefore the purpose of the present work is to carryout a comparative study of the coarsening process of theFe075

Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys after agingat temperatures of 750 850 and 950∘C for several times inorder to know the effect of the Cr addition on the growthkinetics of coarsening and mechanical properties of thisalloy

2 Experimental Details

Two alloy compositions Fe075

Ni010

Al015

and Fe074

Ni010

Al015

Cr001

were melted in an electric arc furnace under anargon atmosphere using high purity Fe (999) Ni (9999)Al (997) and Cr (999) The chemical composition ofalloys was verified pursuing the chemical analysis by theatomic absorption method with a GBS Avanta equipmentbased on a variation of ASTM E-353 standard [11] with anexperimental error between 004 and 026 depending onthe element The actual compositions were Fe-103atNi-152atAl and Fe-99atNi-154atAl-11atCr which arevery close to the nominal one The alloy ingots wereencapsulated in quartz tube under an argon atmosphereand heated at 1100∘C for one week in a tubular electricfurnace in order to destroy the as-cast microstructure andhomogenize the chemical composition Specimens of 30 times30 times 10mm were cut and encapsulated in a quartz tubeunder argon atmosphere to conduct the solution treatmentat 1100∘C for 1 h and then aged at 750 850 and 950∘Cfor times from 5 to 1000 h The solution treated and agedspecimens were preparedmetallographically and etched withan etchant composed of 2 vol- nitric acid in methanoland then observed with secondary electron image (SEI)in a JEM 6300 JEOL scanning electron microscope (SEM)equipped with an energy dispersive spectrometer (EDS) at25 kV The aged specimens of both alloys were also analyzedby X-ray diffraction analysis with Mo K120572 radiation with aSiemens D-5000 equipment in order to confirm the presenceof the ordered 1205731015840 phase The equivalent circus radius ofprecipitates 119903 was measured by means of the precipitate areaon SEM images with an image analyzing system In orderto get representative data 200 measurements were done indifferent zones of the specimensThesemeasurementsmainlycorresponded to precipitates with a cuboid morphology Thevolume fraction of precipitates was evaluated employing thearea method in both the alloy specimens aged at 750 850and 950∘C for 25 50 100 and 200 h STEM analysis of someaged specimens was carried out with the HAADF detectorto obtain a Z-contrast and it was combined with STEM-EDX analysis to know the distribution of chemical elementsin matrix and precipitates of some aged specimens TheVickers hardness HV 0112 s was measured in all the agedspecimens

3 Results and Discussion

31 Microstructural Evolution of Coarsening SEM micro-graphs of the precipitation evolution are shown in Figures1 and 2(a)ndash2(d) for the Fe

075Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys respectively aged at 750 and 950∘C for50 and 200 h Both figures show the presence of the 1205731015840precipitates in the ferritic matrix The 1205731015840 precipitates wereconfirmed to have the B2 (CsCl) crystalline structure asshown in Figure 3 which shows the superreflections for thisphase in bothX-ray diffractograms of the alloys aged at 950∘Cfor 50 h Several diffraction peaks of the 1205731015840 precipitates areoverlapped with those corresponding to the ferrite matrixThe morphology of the 1205731015840 precipitates is rounded cuboidsin both of the aged alloys from the early stages of agingat all temperatures (Figures 1 and 2(a)) The straight sidesof precipitates suggest the presence of a coherent interfacebetween precipitates and matrix The precipitates becomealigned with the ferritic matrix over the course of time(Figures 1 and 2(b)) This alignment has been reported [12]to occur in the lt100gt crystallographic direction of the ferritematrix since it corresponds to the softest one in the bcccrystalline structure This suggests that the alloy specimenshave the lt100gt orientation in the aged specimens A furtheraging promotes the increase in size of precipitates in both ofthe aged alloys The increase in precipitate size is higher asthe aging temperature increases Aging for longer times hasa tendency to form square or rectangular arrays of cuboidprecipitates in both alloys however this fact seems to behigher in the Fe

075Ni010

Al015

alloy aged at 750 and 850∘Cthan that in the other one (Figures 1 and 2(b)) At agingat 950∘C elongated arrays of precipitates are aligned withrespect to the ferriticmatrix in both alloys (Figures 1 and 2(c)-2(d)) Some coalescence of precipitates is observed in thesearrays and the straight sides of some precipitates becomecurved This suggests the loss of coherency between theprecipitates and matrix This characteristic is more noto-rious in the case of the aged Fe

075Ni010

Al015

alloy Thisbehavior seems to be related to a higher elastic-strain effectin this alloy [13] No splitting of precipitates was observedto occur in both the aged alloys The volume fraction ofprecipitates is also indicated in Figures 1 and 2 and this isin general higher for the alloy without chromium howeverthe volume fractions are very close in both alloys aged at750∘C

32 Coarsening Growth Kinetics The average equivalentcircus radius 119903 of 1205731015840 precipitates expressed as 1199033 is plottedas a function of aging time in Figure 4 for the aged Fe

075

Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys This figureshows straight line curves for the different cases which sug-gest that the LSW theory for diffusion-controlled coarseningis followed in this study The LSW theory and modified LSWtheories [1 2] express mathematically the variation of particleradius with time as follows

1199033minus 1199033

119900= 119896119903119905 (1)

where 119903119900and r are the average radius of precipitates at the

onset of coarsening and time 119905 respectively and 119896119903is a

rate constant which can be determined from the slope ofstraight lines in Figure 4 The most adequate value of thetime exponent 119899 was determined using a regression analysisfor each alloy and aging temperature This indicated that


f = 032

(a)

f = 022

(b)

f = 034

(c)

f = 032

2120583m

(d)


Ni010

Al015


f = 031

(a)

f = 019

(b)

f = 032

(c)

f = 023

2120583m

(d)


Ni010

Al015

Cr001



120573998400

Ferrite

Inte

nsity

2120579 (deg)15 20 25 30 35 40 45 50




Ni010

Al015

andFe074

Ni010

Al015

Cr001


r3(n

m3times10

7)

10

8

6

4

2

0

0 200 400 600 800

Aging time (h)




Fe075Ni010Al015


075Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys




075Ni010

Al015


Ni010

Al015

Cr001



074Ni010

Al015

Cr001


075Ni010

Al015

and Fe074

Ni010

Al015

Cr001



074Ni010

Al015

Cr001



A

B


(a)

FeNi

AlCr

1000

800

600

400

200

0

00 01 02 03 04 05 06

Inte

nsity

pro

file (

au)

Length (120583m)

(b)


05

04

03

02

01

00

750 800 850 900 950

FeAlNi

Cr


Mol

e fra

ctio

n

Temperature (∘C)



Ni010

Al015

andFe074

Ni010

Al015

Cr001

alloys



075Ni010

Al015

and Fe074

Ni010

Al015

Cr001



00 02 04 06 08 10 12 14 16 18 20 22

25

20

15

10

05

00

LSW

Prob

abili

ty d

ensit

y

120588

FeNiAl750∘C-50h

(a)

LSW

25

20

15

10

05

00

00 02 04 06 08 10 12 14 16 18 20 22

120588

FeNiAl950∘C-150h

Prob

abili

ty d

ensit

y

(b)

LSW

25

20

15

10

05

00

00 02 04 06 08 10 12 14 16 18 20 22

120588

750∘C-50hFeNiAlCr

Prob

abili

ty d

ensit

y

(c)

LSW

25

20

15

10

05

00

120588

00 02 04 06 08 10 12 14 16 18 20 22


Prob

abili

ty d

ensit

y

(d)


Ni010

Al015

and (c-d) Fe074

Ni010

Al015

Cr001




Ni010

Al015

Cr001


Ni010

Al015



4 Conclusions


Ni010

Al015



0 100 200 300 400 500 600 700 800 900 1000

520

510

500

490

480

470

460

450

440

Aging time (h)

750∘C 850∘C

950∘C




Vick

ers h

ardn

ess

HV

01

12

s


Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys



Acknowledgments


References













75-Ni10-Al15















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




f = 032

(a)

f = 022

(b)

f = 034

(c)

f = 032

2120583m

(d)


Ni010

Al015


f = 031

(a)

f = 019

(b)

f = 032

(c)

f = 023

2120583m

(d)


Ni010

Al015

Cr001



120573998400

Ferrite

Inte

nsity

2120579 (deg)15 20 25 30 35 40 45 50




Ni010

Al015

andFe074

Ni010

Al015

Cr001


r3(n

m3times10

7)

10

8

6

4

2

0

0 200 400 600 800

Aging time (h)




Fe075Ni010Al015


075Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys




075Ni010

Al015


Ni010

Al015

Cr001



074Ni010

Al015

Cr001


075Ni010

Al015

and Fe074

Ni010

Al015

Cr001



074Ni010

Al015

Cr001



A

B


(a)

FeNi

AlCr

1000

800

600

400

200

0

00 01 02 03 04 05 06

Inte

nsity

pro

file (

au)

Length (120583m)

(b)


05

04

03

02

01

00

750 800 850 900 950

FeAlNi

Cr


Mol

e fra

ctio

n

Temperature (∘C)



Ni010

Al015

andFe074

Ni010

Al015

Cr001

alloys



075Ni010

Al015

and Fe074

Ni010

Al015

Cr001



00 02 04 06 08 10 12 14 16 18 20 22

25

20

15

10

05

00

LSW

Prob

abili

ty d

ensit

y

120588

FeNiAl750∘C-50h

(a)

LSW

25

20

15

10

05

00

00 02 04 06 08 10 12 14 16 18 20 22

120588

FeNiAl950∘C-150h

Prob

abili

ty d

ensit

y

(b)

LSW

25

20

15

10

05

00

00 02 04 06 08 10 12 14 16 18 20 22

120588

750∘C-50hFeNiAlCr

Prob

abili

ty d

ensit

y

(c)

LSW

25

20

15

10

05

00

120588

00 02 04 06 08 10 12 14 16 18 20 22


Prob

abili

ty d

ensit

y

(d)


Ni010

Al015

and (c-d) Fe074

Ni010

Al015

Cr001




Ni010

Al015

Cr001


Ni010

Al015



4 Conclusions


Ni010

Al015



0 100 200 300 400 500 600 700 800 900 1000

520

510

500

490

480

470

460

450

440

Aging time (h)

750∘C 850∘C

950∘C




Vick

ers h

ardn

ess

HV

01

12

s


Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys



Acknowledgments


References













75-Ni10-Al15















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




120573998400

Ferrite

Inte

nsity

2120579 (deg)15 20 25 30 35 40 45 50




Ni010

Al015

andFe074

Ni010

Al015

Cr001


r3(n

m3times10

7)

10

8

6

4

2

0

0 200 400 600 800

Aging time (h)




Fe075Ni010Al015


075Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys




075Ni010

Al015


Ni010

Al015

Cr001



074Ni010

Al015

Cr001


075Ni010

Al015

and Fe074

Ni010

Al015

Cr001



074Ni010

Al015

Cr001



A

B


(a)

FeNi

AlCr

1000

800

600

400

200

0

00 01 02 03 04 05 06

Inte

nsity

pro

file (

au)

Length (120583m)

(b)


05

04

03

02

01

00

750 800 850 900 950

FeAlNi

Cr


Mol

e fra

ctio

n

Temperature (∘C)



Ni010

Al015

andFe074

Ni010

Al015

Cr001

alloys



075Ni010

Al015

and Fe074

Ni010

Al015

Cr001



00 02 04 06 08 10 12 14 16 18 20 22

25

20

15

10

05

00

LSW

Prob

abili

ty d

ensit

y

120588

FeNiAl750∘C-50h

(a)

LSW

25

20

15

10

05

00

00 02 04 06 08 10 12 14 16 18 20 22

120588

FeNiAl950∘C-150h

Prob

abili

ty d

ensit

y

(b)

LSW

25

20

15

10

05

00

00 02 04 06 08 10 12 14 16 18 20 22

120588

750∘C-50hFeNiAlCr

Prob

abili

ty d

ensit

y

(c)

LSW

25

20

15

10

05

00

120588

00 02 04 06 08 10 12 14 16 18 20 22


Prob

abili

ty d

ensit

y

(d)


Ni010

Al015

and (c-d) Fe074

Ni010

Al015

Cr001




Ni010

Al015

Cr001


Ni010

Al015



4 Conclusions


Ni010

Al015



0 100 200 300 400 500 600 700 800 900 1000

520

510

500

490

480

470

460

450

440

Aging time (h)

750∘C 850∘C

950∘C




Vick

ers h

ardn

ess

HV

01

12

s


Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys



Acknowledgments


References













75-Ni10-Al15















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




A

B


(a)

FeNi

AlCr

1000

800

600

400

200

0

00 01 02 03 04 05 06

Inte

nsity

pro

file (

au)

Length (120583m)

(b)


05

04

03

02

01

00

750 800 850 900 950

FeAlNi

Cr


Mol

e fra

ctio

n

Temperature (∘C)



Ni010

Al015

andFe074

Ni010

Al015

Cr001

alloys



075Ni010

Al015

and Fe074

Ni010

Al015

Cr001



00 02 04 06 08 10 12 14 16 18 20 22

25

20

15

10

05

00

LSW

Prob

abili

ty d

ensit

y

120588

FeNiAl750∘C-50h

(a)

LSW

25

20

15

10

05

00

00 02 04 06 08 10 12 14 16 18 20 22

120588

FeNiAl950∘C-150h

Prob

abili

ty d

ensit

y

(b)

LSW

25

20

15

10

05

00

00 02 04 06 08 10 12 14 16 18 20 22

120588

750∘C-50hFeNiAlCr

Prob

abili

ty d

ensit

y

(c)

LSW

25

20

15

10

05

00

120588

00 02 04 06 08 10 12 14 16 18 20 22


Prob

abili

ty d

ensit

y

(d)


Ni010

Al015

and (c-d) Fe074

Ni010

Al015

Cr001




Ni010

Al015

Cr001


Ni010

Al015



4 Conclusions


Ni010

Al015



0 100 200 300 400 500 600 700 800 900 1000

520

510

500

490

480

470

460

450

440

Aging time (h)

750∘C 850∘C

950∘C




Vick

ers h

ardn

ess

HV

01

12

s


Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys



Acknowledgments


References













75-Ni10-Al15















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




00 02 04 06 08 10 12 14 16 18 20 22

25

20

15

10

05

00

LSW

Prob

abili

ty d

ensit

y

120588

FeNiAl750∘C-50h

(a)

LSW

25

20

15

10

05

00

00 02 04 06 08 10 12 14 16 18 20 22

120588

FeNiAl950∘C-150h

Prob

abili

ty d

ensit

y

(b)

LSW

25

20

15

10

05

00

00 02 04 06 08 10 12 14 16 18 20 22

120588

750∘C-50hFeNiAlCr

Prob

abili

ty d

ensit

y

(c)

LSW

25

20

15

10

05

00

120588

00 02 04 06 08 10 12 14 16 18 20 22


Prob

abili

ty d

ensit

y

(d)


Ni010

Al015

and (c-d) Fe074

Ni010

Al015

Cr001




Ni010

Al015

Cr001


Ni010

Al015



4 Conclusions


Ni010

Al015



0 100 200 300 400 500 600 700 800 900 1000

520

510

500

490

480

470

460

450

440

Aging time (h)

750∘C 850∘C

950∘C




Vick

ers h

ardn

ess

HV

01

12

s


Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys



Acknowledgments


References













75-Ni10-Al15















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0 100 200 300 400 500 600 700 800 900 1000

520

510

500

490

480

470

460

450

440

Aging time (h)

750∘C 850∘C

950∘C




Vick

ers h

ardn

ess

HV

01

12

s


Ni010

Al015

and Fe074

Ni010

Al015

Cr001

alloys



Acknowledgments


References













75-Ni10-Al15















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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