Microstructure characterization, stress–strain behavior, superelasticity and shape memory effect of Cu–Al–Mn–Cr shape memory alloys

In this study, the Cr was added into Cu–Al–Mn alloys for replacing Cu and Mn, and the microstructure, martensitic transformation, stress–strain behavior, superelasticity and shape memory effect of quaternary Cu–Al–Mn–Cr shape memory alloys were investigated. All the studied alloys exhibit a mixed microstructure consisted of dominant L21 parent, small amounts of A2(Cr) and 2H(γ1′) martensite, as well as a reversible martensitic transformation. Although the alloys are main L21 parent before deformation, partial stress-induced 2H(γ1′) martensite can be stabilized and retained after unloading. Therefore, the same alloy under a certain deformation 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.