High-temperature in-situ microscopy during stress-induced phase transformations in Co49Ni21Ga30 shape memory alloy single crystals

Abstract

Abstract This paper reports on the role of repeated stress-induced martensite transformations at different temperatures (referred to as “training”) on the pseudoelasticity and microstructural evolution of as-grown Co49Ni21Ga30 [001]-oriented shape memory alloy single crystals under compression. The training resulted in a reduction in transformation stress levels and a stable microstructure with a multi-variant configuration reducing the observed transformation strains. Training also improved the recoverability giving way to a large pseudoelastic temperature window of 400°C. In-situ microscopy revealed the martensite stabilization to be due to pinning of moving interfaces especially at temperatures above 120°C. An insight into the evolution of microstructure and stressüstrain behavior in terms of stress hysteresis changes with test temperature is provided, and the possible operant mechanisms are discussed.