In-situ TEM study of stress-induced transformations in CuAlNi

Stress-induced martensitic transformations and twinning processes were studied in thin foils of CuAlNi single crystals strained in-situ in a transmission electron microscope. A detailed structure analysis comprised identification of phases existing under stress and determination of their mutual crystallographic orientation. Three transformation processes were detected: i) transformation of austenite into 2H martensite at low stress levels; ii) twinning/detwinning processes in 2H martensite, and iii) transformation between austenite and 18R martensite at higher stress levels. Nucleation and growth of martensite plates were followed, and morphology of the austenite/martensite habit planes was examined. Existence of planar interfaces between a single variant of 2H martensite and austenite on microscopic level was proved.