Shape memory effect and superelasticity in a “non-shape-memory” alloy

We discovered unexpected shape memory effect and superelasticity in a “non-shape-memory alloy”. For more than half century the shape memory effect (the memory of a predefined “hot” shape upon heating) and superelasticity (huge pseudoelastic deformation) have been known to exist only in a class of shape memory alloys, which are characterized by structural transformation called martensitic transformation. No shape memory effect and superelasticity are expected for a non-martensitic system. Very recently, we report that unexpected shape memory effect and superelasticity in a “non-martensitic” alloy, which is actually a recently discovered “strain glass” alloy Ti-51.5Ni. This alloy does not undergo martensitic transformation but undergo a strain glass transition (being a strain analog of the physically-parallel spin glass). The shape memory effect and superelasticity are found to stem from a stress-induced transformation from the strain glass state to a martensitic state. The discovery of the shape memory effect and superelasticity in the non-martenstic, strain glass alloy may significantly extend the regime of shape memory alloys and may lead to novel applications.

See Yu Wang, Xiaobing Ren, and Kazuhiro Otsuka, PHYSICAL REVIEW LETTERS, 97, 225703 for details.