Destabilization of Ni–Mn–Ga martensite: Experiment and theory

The cyclic temperature- and stress-induced martensitic transformations (MTs) of Ni–Mn–Ga single-crystal alloy with c/a > 1 have been studied both experimentally and theoretically. A destabilizing affect of thermal, mechanical and combined thermomechanical cycling on the martensitic phase has been revealed. It has been shown that the martensite destabilization is caused by the internal stress that arises in the course of the spatial reconfiguration of crystal defects. The effects of cycling have been experimentally studied and quantitatively described in the framework of symmetry-conforming Landau theory. It has been shown that the cycling results in a decrease in the elastic modulus of the martensitic phase, a decrease in the MT temperature, and an increase in the stress value, which triggers the stress-induced MT. An agreement between the experimental and theoretical results has been ascertained.