Ultra-large tensile strains and martensite destabilization observed in high-temperature Ni57.5Mn22.5Ga20.0 single crystal

Tensile stress-strain behavior of Ni57.5Mn22.5Ga20.0 single crystal exhibiting a high-temperature 2M-martensitic phase stable up to 360\degree C has been studied in the course of thermal and mechanical cycling. The ultra-large reversible strains, about 9%, caused by the shape memory and superelasticity effects, have been observed up to 400 \degree C being the instrumental temperature limit. Abnormally large two-way shape memory effect with 9% of strain magnitude has been found. The cycling procedure and the variation of thermal/mechanical routs of the training of samples revealed the destabilization (rejuvenation) of martensite. This physical effect is opposite to the well-known phenomenon of martensite stabilization. A destabilization effect is explained phenomenologically in terms of internal stressing of the alloy sample by the crystal defects.