The first complete atomic-scale view of the structural transformations responsible for the Nitinol’s shape-memory ability has been developed. Despite its industrial popularity, the underlying physics and atomistic mechanics of Nitinol have remained unclear for over 50 years. Shape-memory alloys can remember their original shape and respond to heat to produce desirable shape changes. The shape-memory effect is controlled by transformations mostly between the high-temperature (austenite) and low-temperature (martensite) structures. To elucidate the path of the shape change, structures, and transition states, the team constructed a unique computer code and discovered the transformations include a previously-unidentified stable austenitic structure, intermediate structures, and martensite variants. Helping to identify the origin of this technologically useful effect provides vital information for synthesizing and designing new shape memory materials.
Shape-memory Transformations of NiTi: Minimum-energy Pathways between Austenite, Martensites, and Kinetically-limited Intermediate States