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

TL;DR

This study investigates the high-temperature shape memory and superelasticity in Ni57.5Mn22.5Ga20.0 single crystals, revealing ultra-large reversible strains and martensite destabilization due to internal stresses from defects.

Contribution

It reports the observation of ultra-large reversible strains and martensite destabilization in high-temperature Ni-Mn-Ga single crystals, highlighting a novel destabilization phenomenon opposite to stabilization.

Findings

Reversible strains up to 9% observed at temperatures up to 400°C.

Martensite destabilization (rejuvenation) demonstrated through cycling.

Large two-way shape memory effect with 9% strain magnitude.

Abstract

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.