Structure design of high-performance Cu-based shape memory alloys

The effects of various structure factors on the properties (superelasticity mainly) of Cu-based shape memory alloys (SMAs) were systematically evaluated in this review article through literatures combining with our work. It is concluded that besides the decisive role of grain orientation, the grain boundary (GB) characteristics also play important roles in the superelasticity, which include GB area, GB type, GB morphology and GB direction in descending order of the effect significance. According to the above results, the prior principles of structure design are proposed for high-performance Cu-based SMAs from most to least important: (1) obtaining grain orientation with high phase transformation strain; (2) increasing grain size or reducing GB area; (3) obtaining straight low-energy GBs, especially low-angle GBs; (4) trying to make GB direction parallel to external stress. Consistent with the main or all principles, the bamboo-like-grained and columnar-grained (CG) Cu-based SMAs show excellent comprehensive properties.