Overview of Orientation Dependence of Mechanical Properties in Single-Crystal Superelastic Cu-Al-Mn Shape Memory Alloys

The purpose of this paper is to provide an overview of the crystal orientation dependence of superelasticity, plasticity, and fracture behavior of single-crystal superelastic Cu-Al-Mn shape memory alloy (SMA) bars. In this paper, we prepared 3 single-crystal superelastic Cu-Al-Mn SMA bars of 8-mm diameter and 123 mm length with different crystal orientations. The crystal orientation was measured using electron backscatter diffraction (EBSD). In the tension tests, we applied cyclic tension up to the target strain and consecutive monotonic tension up to the fracture. When the orientation was close to 〈001〉, we observed low Young’s modulus of around 20 GPa, excellent two-step superelasticity with recovery strain of over 15%, large elongation with fracture strain of over 70%. When the orientation was close to 〈101〉, we observed higher Young’s modulus of around 64 GPa, one-step superelasticity of recovery strain around 7%, sudden and strong hardening after the end of the martensitic transformation, and brittle shear failure without plastic deformation at the fracture strain of around 10%. When the orientation was close to 〈111〉, which has been observed for the first time in this study, we observed very high Young’s modulus of around 250 GPa and shear failure after the slight superelastic and plastic deformations at the fracture strain of around 2%. These results provide an overview of the orientation dependence of mechanical properties in single crystal superelastic Cu-Al-Mn SMAs.