Orientation dependence of superelasticity and stress hysteresis in Cu-Al-Mn alloy

Cu-Al-Mn single crystals with subgrains were prepared by cyclic heat treatment, and the orientation dependence of superelasticity was investigated using tensile tests, during which the microstructure of the martensite was observed in situ. The transformation strain result basically agrees with the calculation from the shape strain, but the value is lower than the calculation result and the stress hysteresis is abnormally wide in some samples. The stress-induced forward and reverse martensitic transformation takes place by a single variant in the sample with a normal hysteresis but by multiple variants in the sample with wide hysteresis. The wide hysteresis mainly results from an abnormally low stress for the reverse transformation, which is considered to be caused by competition between the variants. The results suggest that multi-variants can be induced when the loading direction is located on the sides of stereo-triangle, such as (001) to (101), (001) to (111), and (101) to (111), based on Schmid's law.