Shape Memory Alloys

TLDR: Otsuka et al. as mentioned in this paper showed a one-to-one correspondence between shape memory effect and the thermoelastic martensitic transformation in a Cu-AI-Ni alloy.

Abstract: In some alloys, a given plastic strain recovers completely when the con­ cerned alloy is heated above a certain temperature. This phenomenon, shape memory effect (SME), was observed in Au-Cd (1) and In-Tl (2) alloys in the first half of 1950s. However, SME was not a focus of research until it was found in a Ti-Ni alloy (3) in 1963, when the phenomenon was first termed the shape memory effect. A similar phenomenon was found in a Cu-AI-Ni alloy as well (3a). At that time, however, SME was considered to be a peculiar phenomenon limited to the specific Ti-Ni alloy. In 1970, Otsuka & Shimizu (4, 4a) unambiguously demonstrated a one­ to-one correspondence between SME and the thermoelastic martensitic transformation in a Cu-AI-Ni alloy. Thus, they concluded that SME is characteristic of alloys exhibiting thermoelastic martensitic trans­ formations. They ascribed the origin to the crystallographic reversibility of the thermoelastic transformation and the presence of a recoverable deformation mode, i.e. twinning, in thermoelastic alloys. Since then, there