Effect-of-Nb-particles-on-the-flow-behavior-of-TiAl-alloy_2014_Intermetallics

Intermetallics46(2014)22e28

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Intermetallics

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EffectofNbparticlesonthe owbehaviorofTiAlalloy

JianboLia,YongLiua,*,BinLiua,YanWangb,KunZhaoa,YuehuiHea

ab

StateKeyLaboratoryofPowderMetallurgy,CentralSouthUniversity,Changsha410083,PRChinaSchoolofAeronauticsandAstronautics,CentralSouthUniversity,Changsha410083,PRChina

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Articlehistory:

Received12August2013Receivedinrevisedform4October2013

Accepted5October2013

Availableonline9November2013Keywords:

A.Titaniumaluminides,basedonTiAlB.DeformationmapD.Microstructure

abstract

HightemperaturecompressivedeformationbehaviorsofPM-TiAlalloycontainingNbparticles(Tie45Ale5Nbe0.4W/2Nb(at.%))wereinvestigatedattemperaturesrangingfrom1050 Cto1200 C,andstrainratesfrom0.001sÀ1to1sÀ1.The owcurveswereemployedtodevelopconstitutiveequations,andtheapparentactivationenergyofdeformationQwasdeterminedas447.35kJ/mol.Arevisedprocessingmapwasconstructedonthebasisofthe owstress,whichcanaccuratelydescribethedeformationbehaviorsandpredicttheoptimumhotforgingcondition.Theadditionof2%NbparticlesreducesthepeakstressandincreasestheactivationenergyofTiAl-basedintermetallic,however,itincreasestheinstabledomainintheprocessingmap.

Ó2013ElsevierLtd.Allrightsreserved.

1.Introduction

TiAl-basedalloysareofgrowingintereststotheaerospace,automotiveandenergyindustriessincetheyofferaremarkablecombinationoflowdensity,highspeci cmodulusandstrength,goodcreepandoxidationresistance[1].However,lowductilityanddamagetoleranceatroomtemperatureaswellaspoorworkabilityatelevatedtemperaturesrestricttheapplicationsofTiAl-basedalloys[2,3].However,Ward-Closeetal.[4]proposedthatductileparticlescanimprovetheoveralldeformationabilityoftheinter-metallicmatrixandrestrictthegrowthofcracksduringthedeformation.Raoetal.[5]foundthatniobiumparticle-reinforcedTiAlalloyspossessquitepromisingimprovementsinbothmono-tonicfracturetoughnessandcyclicfatiguethresholdcomparedtomonolithicTiAl.Liuetal.[6]showedthatthepresenceofbphasecangreatlyimprovethedeformabilityathightemperatures,andthecontentofbphasecanbeincreasedbyintroducingNb.Mean-while,itisbelievedthatgrainre nementbyhotworkingisaneffectiveapproachtoenhancetheoverallperformanceofTiAlal-loys[7].Thus,itisofgreatimportancetostudythehotdeformationbehaviorsofthesealloys.

Inrecentyears,processingmapshavebeendevelopedbasedontheDynamicMaterialsModel(DMM),describingtheabilityofthematerialtodissipatepowerthroughmicrostructuralchangesduringdeformationprocessing.Themapshavebeenusedtoevaluatethethermaldeformationmechanismsofmagnesium

alloys,austeniticsteel,Ni-basedsuperalloys,titaniumalloysaswellasintermetallics.However,fewstudieshavefocusedontheapplicationofDMMforintermetallicscontainingductileparticles.

Inthisstudy,arevisedprocessingmapwasconstructedbycombiningtheinstabilitymapandthepowerdissipationmapinordertoachieveanindepthunderstandingofthedeformationmechanisms.2.Experimental

PowdermetallurgytechniquehasbeenexploredtosynthesizePM-TiAlalloybymixingalloypowderwithanominalcompositionofTie45Ale5Nbe0.4W(at.%)andNbelementalpowder(2%,at.%)followedbyhotisostaticpressing(HIP)at1250 Cfor5handapressureof170MPa.Thecompressionspecimenswithadiameterof8mmandaheightof12mmwerecutbyelectric-dischargemachining,andthecompressiontestswereconductedattemper-aturesrangingfrom1050 Cto1200 C,andstrainratesfrom0.001sÀ1to1sÀ1usingathermecmastor-Zthermalsimulationmachine.Thesampleswereheatedat5 C/s,andhomogenizedfor5minatthedeformationtemperature.Thesamplesweredeformedwithamaximumnominaldeformationof60%, nallythesampleswerequenchedtoroomtemperaturetopreservethedeformedmicrostructure.Inordertoreducethefriction,graphitepaperandglassprotectivelubricantwereused.

Themicrostructureswerecharacterizedbyscanningelectronmicroscopy(SEM)inback-scatteredelectron(BSE)mode,trans-missionelectronmicroscopy(TEM)andX-raydiffractiontechnique(XRD).

*Correspondingauthor.Tel.:þ8673188830406;fax:þ8673188710855.E-mailaddresses:yonliu11@yahoo.com.cn,yonliu@mail.csu.edu.cn(Y.

Liu).0966-9795/$eseefrontmatterÓ2013ElsevierLtd.Allrightsreserved.doc.xuehai.net

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