Investigations On The Microstructures And Properties Of Cu-Al-Mn-(Cr,V,Ti)Shape Memory Alloys

Cu-Al-Mn-based SMAs have been applied in several practical applications for the advantages of easy fabrication,good shape memory properties and low manufacturing cost.However,the critical stress for stress-inducing martensitic transformation and the fatigue strength of Cu-Al-Mn SMAs are very low,which limit their further practical applications.In this study,three types of Cu-Al-Mn-based SMAs were prepared by alloying Cr,V and Ti,including Cu-Al-Mn-Cr,Cu-Al-Mn-V and Cu-Al-Mn-Ti,respectively.Then their microstructures,martensitic transformation characteristics,mechanical and shape memory behaviors were investigated by means of optical micrograph,XRD,EPMA,DSC,compressive and TMA tests.The details of the results are described as follows:(1)Cu-Al-Mn-Cr SMAs exhibit a mixed microstructure consisted of dominant L21 parent,A2(Cr)phase and small amounts of 2H(?'1)martensite,as well as a reversible martensitic transformation.Although the alloys are main L21 parent before deformation,partial stress-induced 2H(?'1)martensite can be stabilized and retained after unloading.Therefore,the same alloy under a certain deformation temperature(room temperature)not only exhibits superelasticity property during deformation,but also the deformed alloy also shows shape memory effect when heated.The results further show that Cu-12.8Al-7.5Mn-2.5Cr alloy has a good superelasticity strain of 2.9%as well as a shape memory effect of 1.5%.Cu-12.7Al-6.9Mn-1.8Cr alloy possesses much the best superelasticity strain close to 5.0%under a pre-deformation of 10%and a shape memory effect of 2.0%.The best shape memory effect up to 2.5%with 10%of pre-deformation and a superelasticity strain of 2.8%are obtained in Cu-12.5Al-5.8Mn-4.1Cr alloy.(2)Cu-Al-Mn-V SMAs have complex microstructure consisted of L21 parent,8(V,Mn)phase and 2H(?'1)martensite.The amounts of 8(V,Mn)phase and 2H(?'1)martensite increase with the increase of V content.The results further show that the stabilization of stress-induced 2H(?'1)martensite from L21 parent occurs during deformation.The superelasticity and shape memory effect are summarized to three situations.Situation I includes Cu-12.8Al-9.4Mn-1.8V and Cu-13.1Al-8.6Mn-2.1V,which have excellent superelasticity strains being up to 5.4%and 3.9%respectively.Cu-12.9A1-6.8Mn-4.0V and Cu-13.4A1-6.3Mn-4.5V alloys are situation II,and exhibit good shape memory effects being up to 3.5%and 3.9%respectively.The superelasticity and shape memory effect of Cu-13.4Al-8.7Mn-2.5V alloy that is situation III are between the above two situations.(3)Cu-Al-Mn-Ti SMAs have a mixed microstructure consisted of dominant Cu2AlMn(L21parent),Cu2TiAl phase(also L21 structure)and 2H(?'1)martensite.With the increasing of deformation,partial stress-induced 2H(?'1)martensite from Cu2AIMn parent can be stabilized and retained after unloading.The results further show that the superelasticity decreases with the increase of Ti content.Cu-12.9Al-8.3Mn-0.5Ti alloy has a good superelasticity strain of 4.6%and a shape memory effect of 1.5%.While increasing the Ti content,Cu-12.3Al-8.6Mn-1.9Ti and Cu-12.8Al-7.7Mn-2.6Ti alloy possess better shape memory effect up to 2.3%and 2.5%,respectively.However,with the further addition of Ti,the shape memory effects decrease.Cu-13.7Al-7.4Mn-4.3Ti alloy only has a max superelasticity strain of 1.8%as well as the best shape memory effect of 1.1%.