Stress state effect on martensitic structures in shape memory alloys

Results of tension/compression thermomechanical tests, transmission electron microscopy TEM and X-ray investigations of deformed Cu–Al–Zn–Mn polycrystals are compared with the predictions of a simple model providing upper bounds for tension/compression transformation strains of a Cu-base shape memory alloy polycrystal. The model is based on extensive single-crystal investigations of the anisotropies associated with martensitic transformations, and explains why the Cu–Al–Zn–Mn polycrystal exhibits tension/compression asymmetry and why it transforms into a mixture of β1′ and γ1′ martensite phases, the fraction of which depends on the applied stress state and temperature.