日本东北大学发现能使铜基形状记忆合金的晶粒扩大至数厘米的热处理方法

日本东北大学发现能使铜基形状记忆合金的晶粒扩大至数厘米的热处理方法IntroductionShape memory alloys (SMAs) have been developed in recen

日本东北大学发现能使铜基形状记忆合金的晶粒扩大 至数厘米的热处理方法 Introduction Shapememoryalloys(SMAs)havebeendevelopedinrecent yearssincetheyexhibituniquepropertiesofshapememoryand superelasticity.Thesematerialsretaintheiroriginalshapewhen heatedandreturntotheirmemorizedshapesuponcooling. AmongSMAs,copper-basedshapememoryalloys(Cu-based SMAs)havebeenwidelyresearchedbecauseoftheirhigh dampingcapacity,lowdensity,andbetterbiocompatibility. However,theapplicationofthesematerialshasbeenlimiteddue totheirlowfatigueresistanceandpoorworkability.Oneofthe waystoovercometheselimitationsistocontrolthe microstructureofCu-basedSMAs.Hence,thispaperaimsto investigatetheheattreatmentmethodthatcansignificantly increasethegrainsizeofCu-basedSMAs. Background Ashapememoryalloycomprisestwophases,namely,a parentphaseandamartensiticphase.Theparentphaseisa high-temperaturephase,whereasthemartensiticphaseisa low-temperaturephase.Therearetwogeneralwaystoachievethe shapememoryeffectinSMAs:onemethodistoalloymetals,and theotheristoinduceaphasetransformationthrough temperaturechanges.Intheformermethod,Cu-basedSMAsare composedofacoppermatrixandaprecipitatedsecondphase. Thesecondphasehasadifferentlatticestructurefromthatofthe coppermatrix,andhencethephasetransformationprocess generatestheshapememoryeffect.Inthelattermethod,heat treatmentisusedtocontrolthemicrostructureofSMAs,which allowstheformationoflargergrains.Increasingthegrainsize enablesimprovedmechanicalpropertiesofSMAs,includingbetter fatigueresistanceandimprovedductility. Method TheexperimentwasconductedusingaCu-Al-Nialloy,which hasgoodshapememoryandsuperelasticity.Thealloywascast intoarod-shapedingot,andafterhomogenization,itwashot