Stress-induced martensitic transformations and twinning processes were studied in thin foils of CuA1Ni single crystals strained in situ in a transmission electron microscope. The nucleation and growth of the martensite plates were monitored for three transformation pro-cesses known from bulk experiments: (i) the transformation of austenite into 2H martensite at low-stress levels; (ii) the twinning/detwin-ning processes in 2H martensite; and (iii) the transformation between austenite and 18R martensite at higher stress levels. Themorphology of the austenite/martensite habit planes was examined, and the existence of planar interfaces between a single variant of 2H martensite and austenite on the microscopic level was proven.
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