Giant two-way shape memory effect in high-temperature Ni-Mn-Ga single crystal

A perfect two-way shape memory effect (TWSME) with reversible strain of about 9% has been found in the high-temperature Ni57.5Mn22.5Ga20.0 single crystal transforming into 2M non-modulated martensitic phase. Two thermal/mechanical treatment routes were utilized in the experimental procedures. The outstanding high-temperature TWSME is observed as a result of tensile stress-strain cycling along <100> axis involving huge superelastic strains due to stress-induced martensitic transformation. It is argued that the TWSME is related to the anisotropic internal stresses produced by a network of lattice defects. The defects are generated in the course of oriented growth/shrinkage of the dominating martensitic variant in the tensile sample.