完整高熵合金课件

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)DiscoveryofhighentropyalloysIn2004,MulticomponentFeCoNiCrMnalloyfirstlyreportedbyCantorB.withasimplefccsolid-solutionstructure.CantorBetal.MSEA,2004,375-377:213-218.DefinitionofhighentropyalloysStillin2004,theconceptofhighentropyalloywasfirstlyintroducedbyYehJWYehJWetal.AdvEngMater,2004,6:299-303.SimplephaseformationbutcomplexmetallurgicalphenomenonCu-ZrbinaryalloysystemTheGibbsPhaseRuleP=N+1-FWhenN=5,P=6FeCoNiCrMnActuallyHEAsalloyhaveasimplesolid-solutionstructure(mainlyfccorbcc)!!FeaturesofHEAs——severelatticedistortionLatticedistortionSolutionstrengtheningeffectZhou,etal.ApplPhysLett,2008,92:241917SenkovON,etal.Intermetallics,2011,19:698FeaturesofHEAs——sluggishdiffusion?ConstituentelementsintheHEAmatrixdiffusemuchslowlyovertheentiretemperaturerange?ThediffusioncoefficientofNiisthesmallestamongthatofallconstituentsTsaietal.ActaMater2013;61:4887FeaturesofHEAs——highphasestability1400oC19hAs-castAftercompressionat1073KSenkovetal.Intermetallics2011;19:698-706?Formationofasinglebccphase?Thebccphaseishighlystableupto1600oCFeaturesofHEAs——cocktaileffect?theeffectindicatesthattheunexpectedpropertiescanbeobtainedaftermixingmanyelements,whichcouldnotbeobtainedfromanyoneindependentelement.ExtremelyhightoughnessofatypicalfccHEA?ThefracturetoughnessofBerndGludovatzetal.Science2014,345:1153FeCoNiCrMnexceeds210MPa·m-1/2Abnormallow-temperaturemechanicalproperties?Withthedecreaseoftestingtemperature,bothtensilestrengthandductilityareincreased;?Thefracturetoughnesskeptalmostunchanged;Promisinghigh-temperaturemechanicalpropertiesofbccHEAsSenkovetal.Intermetallics2011;19:698-706?Highyieldstrengthattemperaturesupto1600o?CThestrongresistancetohigh-temperaturesoftening,ascomparedtothesuperalloysInterestingphysicalpropertiesofHEAs:discoveryofsuperconductivity?Ta34Nb33Hf8Zr14Ti11HEApossessesanbody-centeredcubicstructureoflatticeparametera≈3.36?.?ItisatypeIIsuperconductorwithatransitiontemperatureTc≈7.3KP.Ko?eljetal.PRL2014,113:107001Diffusionbarriermaterials?Highphasestability----nointeractionwithsubstrates;?Lowdiffusionkinetics----highdiffusionresistanceatelevatedtemperatures15TheresearchactivitiesonHEAsatUSTBProgressinMaterialsScience,2014;61:1-93OurpurposeDesigntheFeCoNiCrMnbasedHEAsforhigh-temperatureapplicationsContent?Phaseformationandstability?Graingrowthatelevatedtemperatures?Deformationbehavior?Alloyingeffects(toenhancehigh-Tmechanicalperformance)1.Phaseformationandstabilityareinfluencedbynotonlychemistrybutalsoprocessingconditions2.Effectsofalloyingadditionsonphaseformation,stabilityandpropertiesarenotassimpleasexpectedPhaseformationintheas-castFeCoNiCrMn?Basicallythealloyhasasinglefccphasebutwithasmallfractionofunidentifiedphase(Cr2Mnoxide?)TheFeCoNiCrMnhighentropyalloyshowedhighphasestability(a)(b)(c)?ThesinglefccphaseintheFeCoNiCrMnalloyisstableevenafter30daysannealingat950oCTheFeCoNiCrMnhighentropyalloyshowedhighphasestability(b)(c)?Textureseemschangedwiththeprocessingconditions?Nosecondphasewasformedduringtherolling/annealingprocessesContent?Phaseformationandstability?Graingrowthatelevatedtemperatures?Deformationbehavior?AlloyingeffectsGraingrowthbehavioroftheFeCoNiCrMnhighentropyalloywasstudiedindetail70%coldrolled850C/1h850C/2h850C/2h925C/1h925C/2h925C/3.5hGraincoarseningexhibitedaclassicalpowerlawbehaviorintheFeCoNiCrMnalloy?n=3andD0=1.0mm?nislargerthan2whichisforLiuetal.,ScriptaMaterialia2013;68:526the“ideal”graingrowthinsingle-phasepurematerialsTheapparentactivationenergyforgraingrowthsuggeststhatsluggishdiffusionindeedoccurred?TheQvalueismuchhigherthanthatforAISI304LN-1stainlesssteels,whichisonlyabout150kJmolThehardnessvaluesatdifferenttemperaturescloselyfollowtheclassicalHall–Petchrelationship?Thesofteningmainlyfromgraincoarsening?TheKHPislargerthan600Mpamm-0.5(theupper-boundforfccmetals),suggestingthatgrainboundaryhardeningefficiencyisobviouslyhigherContent?Phaseformationandstability?Graingrowthatelevatedtemperatures?Deformationbehavior?AlloyingeffectsIn-situneutrondiffractionstudyofdeformationbehavioroftheFeCoNiCrMnalloywasconductedVULCANsystematSpallationNeutronScattering,OakRidgeNationalLaboratory

FCC(111)(200)Relative

Intensity,

a.

u.(331)(311)(222)(220)1.0dspacing,Angstrom1.52.0Wuetal.,Appl.Phys.Letts.2014;104:051910Stress

Increase

Strongelasticanisotropywasobservedduringthetensileloading?Thelatticestrainchangeisstronglydependentonthegrainorientations?The{200}planeshavethelowestelasticmoduluswhilethe{331}planeshavethehighest?Young'smodulusanisotropy(E[111]/E[100])is1.98,closetothatofNi(2.17)butsmallerthanthatoftypicalfccsteels(3.20)Modulus:GPaDevelopmentofatexturedstructureduringthetensiledeformation?Thepeakintensityofthe{220}and{200}reflectionsdecreased,whilethatofthe{111}reflectionsincreased?TexturalevolutionofthecurrentHEAduringtensionappearstobesimilartothoseoftypicalFCCmetalsandalloys,forexample,polycrystallinecopperwithcolumnargrainsThesinglecrystalelasticconstantsofthecurrentHEAweredeterminedbytheKroner'smodelThecubicelasticanisotropyfactor?Theshearanisotropywascalculatedas2.84,muchsmallerthanthatoftheternaryFeCrNialloy(3.77),butclosetothatofthepureFCC-Ni(2.51),manifestingthattheelasticanisotropybehaviorofthecurrentHEAisclosetothatofitsFCCcomponent,i.e.,pureNi.Theexperimentallydeterminedpeakbroadeningdatacanrevealthedislocationtypesduringdeformation?Theslopeintheaboveplotis2.189,whichseemslikeabalancingvaluefortheedge(1.492)andscrew(2.298)dislocations,butclosetothatofthe<110>screwdislocation?Arepresentativebrightfieldimagewithwiggleddislocationsinadeformedspecimen,suggestingamixeddislocationcharacteristicsFlowbehavioratdifferenttemperaturesandstrainrateswereinvestigated?Thetemperatureisinbetween1023Heetal.,Intermetallics55,2014;9-14.and1123K?Thestrainraterangesfrom6.410×10-7to8.013×10-4s-1Steady-statedeformationbehaviorofFeCoNiCrMnTheNortonEquation?RegionIIwithahighstressexponentatthehighstrainrates(orstresses)whileRegionIwithalowstressexponentatthelowstrainrates(orstresses)?Theactivationenergyintworegionsarecomparabletothatforlatticediffusion.Forexample,Ni(317.5kJ/mol),Cr(292.9kJ/mol),andMn(288.4kJ/mol)Thenormalizedplotindicatesthatthedataobtainedatvarioustemperatures(1023-1123K)collapseintoonesinglemastercurve?Inthehighstrainrateregime,nis~5andtheactivationenergyis~330kJ/mol,suggestingadislocation-climbmechanismandtheslowestdiffusingspeciesNicontrolstherateprocess.?Inthelowstrainrateregime,nis<3andtheactivationenergyis~280kJ/mol,suggestingthatthemechanismisthedislocationglidingandthedeformationrateiscontrolledbythediffusionofoneoftheconstituentelementswhichactsasthesoluteatom.1.Relativelylowersteadystateflowstressthansuperalloys2.OxidationresistanceislowduetohighlyactiveelementMnContent?Phaseformationandstability?Graingrowthatelevatedtemperatures?Deformationbehavior?Alloyingeffects—AleffectsAdditionofAlinthe(FeCoNiCrMn)100-xAlxalloysinducedaphasetransitionfromfcctobccstartingatAl8Heetal.,ActaMater.2014;62:105.MicrostructureobservationfurtherconfirmsthephasetransitionresultedfromtheAladdition?BccphasebecomesdominantinalloyAl13,Al14andAl16,andtheminorfccphasemainlyliesinthebccgrainboundaries.TEMcharacterizationrevealsthedetailedphasecharacteristicsThecubic-shapedparticlesareorderedB2whiletheinter-precipitateareaisdisorderedA2.fcc:74.6%.Thecubic-shapedprecipitatesbecomeslightlysmallerbutmoreclose-packed.fcc:<20%sphericalA2particles(～100nm)embeddedintheB2matrix.Limitedfccphaseexistedonlyontheboundariesofthebccgrains.SimilartoAl16,butthefccparticlesdisappearcompletely.TensilepropertiesandhardnessasafunctionoftheaddedAlcontent?StrengthisincreasedbuttheductilityisdecreasedasAlis?addedThealloysbecametoobrittle?onceAlexceeds11%HardnessalsosharplyincreaseswiththeAllevelandapproaches538HVinAl14Changeinthelatticeconstantcanexplainthetensiledeformationbehaviorforthesinglefccalloys?LatticeconstantislinearlyincreasedwithAlinregionI,suggestingasolutionstrengtheningeffectcausedbytheenlargedlatticedistortionThetensilepropertiesofthealloyswithduplexstructurescanbeexplainedbythesimplerule-of-mixture?ThecompositemodeloffersreasonableinterpretationforthestrengthincrementofthealloysinregionII.?Al11alloyhavefracturestrengthof1174Mpaandtensileductilityof7.7%.?alloyswith>11%AlaretoobrittletobedeformedduetoformationoforderedBCCstructures.SummaryPhaseformationandstability--high(homogenization,longtermaging,rolling)GraingrowthatAleffects--hightemperaturessolution--slowstrengtheningFeCoNiCrMnalloyDeformationbehavior--RT:similartoNi,mixdislocationsHT:highstrainrate,dislocationclimblowstrainrate,dislocationglideHigh-TmaterialsHardeningmechanismsurgentlyneededintheFeCoNiCrHEAsystem?Secondaryp