高熵合金

FeCoNiCrMn高熵合金的组织稳定性及变形行为吕昭平教授北京科技大学新金属材料国家重点实验室AcknowledgementsStudents:W.H.Liu,S.Y.Li,H.L.HuangandZ.F.LeiCollaborators:H.Wang,Y.Wu,andX.J.LiuNationalsciencefoundationofChina(Nos.51010001,51001009,and51271212)“111”Program(B07003)ProgramforInnovativeResearchTeaminUniversityTraditionalalloysaremostlybasedononeprimaryelementSteels(Fe),Alalloys,Tialloys,Mgalloys,Supperalloys(Ni)DiscoveryofhighentropyalloysCantorBetal.MSEA,2004,375-377:213-218.In2004,MulticomponentFeCoNiCrMnalloyfirstlyreportedbyCantorB.withasimplefccsolid-solutionstructure.YehJWetal.AdvEngMater,2004,6:299-303.DefinitionofhighentropyalloysStillin2004,theconceptofhighentropyalloywasfirstlyintroducedbyYehJWSimplephaseformationbutcomplexmetallurgicalphenomenonCu-ZrbinaryalloysystemActuallyHEAsalloyhaveasimplesolid-solutionstructure(mainlyfccorbcc)!!TheGibbsPhaseRuleP=N+1-FWhenN=5,P=6FeCoNiCrMnFeaturesofHEAs——severelatticedistortionLatticedistortionZhou,etal.ApplPhysLett,2008,92:241917SenkovON,etal.Intermetallics,2011,19:698SolutionstrengtheningeffectTsaietal.ActaMater2013;61:4887ConstituentelementsintheHEAmatrixdiffusemuchslowlyovertheentiretemperaturerangeThediffusioncoefficientofNiisthesmallestamongthatofallconstituentsFeaturesofHEAs——sluggishdiffusionSenkovetal.Intermetallics2011;19:698-706As-castAftercompressionat1073KFormationofasinglebccphaseThebccphaseishighlystableupto1600oC1400oC19hFeaturesofHEAs——highphasestabilityFeaturesofHEAs——cocktaileffecttheeffectindicatesthattheunexpectedpropertiescanbeobtainedaftermixingmanyelements,whichcouldnotbeobtainedfromanyoneindependentelement.ExtremelyhightoughnessofatypicalfccHEABerndGludovatzetal.Science2014,345:1153ThefracturetoughnessofFeCoNiCrMnexceeds210MPa·m-1/2Abnormallow-temperaturemechanicalpropertiesWiththedecreaseoftestingtemperature,bothtensilestrengthandductilityareincreased;Thefracturetoughnesskeptalmostunchanged;Highyieldstrengthattemperaturesupto1600oCThestrongresistancetohigh-temperaturesoftening,ascomparedtothesuperalloysPromisinghigh-temperaturemechanicalpropertiesofbccHEAsSenkovetal.Intermetallics2011;19:698-706Ta34Nb33Hf8Zr14Ti11HEApossessesanbody-centeredcubicstructureoflatticeparametera≈3.36Å.ItisatypeIIsuperconductorwithatransitiontemperatureTc≈7.3KP.Koželjetal.PRL2014,113:107001InterestingphysicalpropertiesofHEAs:discoveryofsuperconductivity15DiffusionbarriermaterialsHighphasestability----nointeractionwithsubstrates;Lowdiffusionkinetics----highdiffusionresistanceatelevatedtemperaturesTheresearchactivitiesonHEAsatUSTBProgressinMaterialsScience,2014;61:1-93OurpurposeDesigntheFeCoNiCrMnbasedHEAsforhigh-temperatureapplicationsContentPhaseformationandstabilityGraingrowthatelevatedtemperaturesDeformationbehaviorAlloyingeffects(toenhancehigh-Tmechanicalperformance)1.Phaseformationandstabilityareinfluencedbynotonlychemistrybutalsoprocessingconditions2.Effectsofalloyingadditionsonphaseformation,stabilityandpropertiesarenotassimpleasexpectedPhaseformationintheas-castFeCoNiCrMnBasicallythealloyhasasinglefccphasebutwithasmallfractionofunidentifiedphase(Cr2Mnoxide?)(b)(a)(c)TheFeCoNiCrMnhighentropyalloyshowedhighphasestabilityThesinglefccphaseintheFeCoNiCrMnalloyisstableevenafter30daysannealingat950oCTheFeCoNiCrMnhighentropyalloyshowedhighphasestability(b)(a)(c)(b)(a)(c)TextureseemschangedwiththeprocessingconditionsNosecondphasewasformedduringtherolling/annealingprocessesContentPhaseformationandstabilityGraingrowthatelevatedtemperaturesDeformationbehaviorAlloyingeffects850C/1h850C/2h850C/2h70%coldrolled925C/1h925C/2h925C/3.5hGraingrowthbehavioroftheFeCoNiCrMnhighentropyalloywasstudiedindetailGraincoarseningexhibitedaclassicalpowerlawbehaviorintheFeCoNiCrMnalloyn=3andD0=1.0mmnislargerthan2whichisforthe“ideal”graingrowthinsingle-phasepurematerialsLiuetal.,ScriptaMaterialia2013;68:526TheapparentactivationenergyforgraingrowthsuggeststhatsluggishdiffusionindeedoccurredTheQvalueismuchhigherthanthatforAISI304LNstainlesssteels,whichisonlyabout150kJmol-1ThehardnessvaluesatdifferenttemperaturescloselyfollowtheclassicalHall–PetchrelationshipThesofteningmainlyfromgraincoarseningTheKHPislargerthan600Mpamm-0.5(theupper-boundforfccmetals),suggestingthatgrainboundaryhardeningefficiencyisobviouslyhigherContentPhaseformationandstabilityGraingrowthatelevatedtemperaturesDeformationbehaviorAlloyingeffectsIn-situneutrondiffractionstudyofdeformationbehavioroftheFeCoNiCrMnalloywasconductedWuetal.,Appl.Phys.Letts.2014;104:051910VULCANsystematSpallationNeutronScattering,OakRidgeNationalLaboratory1.01.52.0StressIncreaseFCC(111)(200)(220)(311)(222)RelativeIntensity,a.u.dspacing,Angstrom(331)Modulus:GPaStrongelasticanisotropywasobservedduringthetensileloadingThelatticestrainchangeisstronglydependentonthegrainorientationsThe{200}planeshavethelowestelasticmoduluswhilethe{331}planeshavethehighestYoung’smodulusanisotropy(E[111]/E[100])is1.98,closetothatofNi(2.17)butsmallerthanthatoftypicalfccsteels(3.20)DevelopmentofatexturedstructureduringthetensiledeformationThepeakintensityofthe