Ultrafine-Grained-AlCoCrFeNi2-1-Eutectic-High-Entr

Mater.Res.Lett.,2016fine-GrainedAlCoCrFeNi2.1EutecticHigh-EntropyAlloyI.S.Wania,T.Bhattacharjeeb,S.Sheikhc,Y.P.Lud,S.Chatterjeea,P.P.Bhattacharjeea∗,S.GuocandN.Tsujib,eaDepartmentofMaterialsScienceandMetallurgicalEngineering,IITHyderabad,Kandi502285,Telangana,India;bDepartmentofMaterialsScienceandEngineering,KyotoUniversity,YoshidaHonmachi,Sakyo-ku,Kyoto,606-8501Japan;cDepartmentofMaterialsandManufacturingTechnology,ChalmersUniversityofTechnology,SE-41296Gothenburg,Sweden;dKeyLaboratoryofSolidificationControlandDigitalPreparationTechnology(LiaoningProvince),SchoolofMaterialsScienceandEngineering,DalianUniversityofTechnology,Dalian116024,People’sRepublicofChina;eElementsStrategyInitiativeforStructuralMaterials(ESISM),KyotoUniversity,Japan(Received5February2016;finalform27February2016)Thedevelopmentofmicrostructureandmechanicalpropertieswasinvestigatedinaheavilycold-rolledandannealedAlCoCrFeNi2.1high-entropyalloy.Theas-castalloyhavingaeutecticmorphologyconsistingofalternatebandsoforderedL12andB2phaseswas90%cold-rolled.ThedeformedmicrostructureshowedprofuseshearbandinganddisorderingoftheL12,butnotransformationoftheB2phase.Aduplexmicrostructureconsistingofultrafineequiaxedgrains(∼0.60μm)ofdisorderedfacecenteredcubicandB2wasobservedafterannealingat800°C.Theannealedmaterialshowedremarkablestrength–ductilitycombinationhavingultimatetensilestrength∼1.2GPaandelongationtofailure∼12%.Keywords:High-EntropyAlloys,OrderedPhases,Cold-Rolling,Annealing,PropertiesImpactStatement:AlCoCrFeNi2.1eutecticHEAwithorderedL12andB2phasescanbethermo-mechanicallyprocessedtoachieveultrafinestructureandremarkablestrength-ductilityproperties.High-entropyalloys(HEAs)aremulticomponentalloysoriginallybasedonthenovelalloydesignapproachofmixingfiveormoreelementsinequiatomicornear-equiatomicproportions.[1]Despitethepresenceofsev-eralconstituents,theHEAscanshowthepresenceofsinglephaseswithsimplestructuresuchasFCCorBCC,orFCC+BCC.[1]Thishasbeenattributedtothehighentropyofmixingofalargenumberofcom-ponentsinequiatomicornear-equiatomicproportions,whicheffectivelyreducesthefreeenergy.[1,2]How-ever,recentinvestigationshaveshownthathighentropyofmixingaloneisnotsufficienttoexplainthephase*Correspondingauthor.Email:[e-mail],equiatomicHEAswiththesamenumberofconstituentsmayconsistofmul-tiplephasesdependingontheconstituentelements,[3]whilenon-equiatomicalloyscanexistassingle-phasesolidsolutionhavingsimplestructures,[4]Therefore,thephaseformationinHEAsisguidednotonlybythenum-berofcomponents(i.e.configurationalentropy),butalsobythetypeoftheconstituentelements.ThedefinitionandrulesgoverningthephaseformationinHEAsarematterofgreatinterestanddebateatpresent.[5,6]Nevertheless,theHEAshavegeneratedconsider-ableresearchattentionduetotheirseveralattractive©2016TheAuthor(s).PublishedbyTaylor&Francis.ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommonsAttributionLicense(),whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited.Downloadedby[183.82.212.137]at01:1926March2016Mater.Res.Lett.,2016andintriguingmechanicalproperties.[4,5,7–15]Inordertofurtheroptimizethestrength–ductilitycombination,multiphaseHEAsconsistingofductileandhardphaseshavebeensuggested.[16]Thedevelopmentofnon-equiatomiclamellareutecticHEAsisanoteworthyapproachinthisdirection.[16,17]Itisenvisagedthatthermo-mechanicalprocessingcanfurtherenhancethepropertiesofthesealloys,[18]butneedstobeclarifiedindepth.Inthepresentwork,theeffectofheavycold-rollingandannealingonmicrostructureandpropertiesofEHEAisinvestigatedforthefirsttime.Thetar-getalloywithanominalcompositionofAlCoCrFeNi2.1(elementsinatomicratios)waspreparedbyarc-meltingamixtureoftheconstituentelements(puritybetterthan99.9%)inaTi-getteredhigh-purityargonatmosphere.Themeltingwasrepeatedatleastfivetimestoachieveagoodchemicalhomogeneityofthealloy.Themoltenalloywassuction-castintoa15mm(width)×90mm(length)×3mm(thickness)coppermold.Smallpieces(dimensions:20mm(length)×15mm(width))wereextractedfromtheas-castmaterialandsubjectedtomulti-passcold-rollingto∼90%reductioninthickness(finalthickness∼300μm)usingalaboratoryscaletwo-highrollingmachine(Fenn,USA)having140mmdiameterrolls.Samplesformicrostructuralandtensilestudieswereobtainedfromthecold-rolledsheetsandsubsequentlyannealedat800°Cfor1hourtoobtainafullyrecrystallizedmicrostructure.Themicrostruc-turalcharacterizationofthesamplesatdifferentlengthscaleswascarriedoutusingelectronbackscatterdiffrac-tion(EBSD)system(OxfordInstruments,UK)mountedonascanningelectronmicroscope(Carl-Zeiss,Ger-many;Model:SUPRA40)andtransmissionelectronmicroscope(TEM)(JEOL2010)operatedat200KV.ThesamplesforEBSDandTEMwerepreparedusingstandardelectropolishingtechniques(electrolyte:90%ethanol+10%perchloricacid).Tensiletestswerecar-riedoutatambienttemperatureusingafloor-mountedtestingmachine(Shimadzu,Japan)usinganinitialstrainrateof8