In situ synchrotron X-ray microdiffraction analysis of thermomechanically induced phase transformations in Cu-Al-Ni shape-memory alloy

Phase transformations in a single-crystal Cu-Al-Ni shape-memory alloy induced by thermomechanical effects were investigated in situ by high-resolution synchrotron X-ray microdiffraction. Contrary to the common belief, austenite texture maps revealed that austenite-to-martensite transformation occurred during heating of the partially transformed material under fixed specimen elongation. Twinned and detwinned types of martensite coexisted during this austenite-to-martensite phase transformation. Twinning and detwinning structures evolved to accommodate changes in stress and strain generated in the temperature-varying environment. Small amounts of austenite exhibiting distorted crystallographic orientation were detected in regions of stress-induced martensite during heating of the partially transformed material. The results of this investigation provide insight into intriguing stress rate-dependent phenomena intrinsic of shape-memory alloys and elucidate complex phase transformations due to thermal and mechanical stress effects.