On the anisotropy of martensitic transformations in Cu-based alloys

Tension/compression thermomechanical experiments were performed on oriented Cu–Al–Ni shape memory alloy single crystals. Response of the single crystals in thermomechanical loads was strongly temperature dependent and anisotropic, i.e. dependent on the orientation of the load axis and sense of the load. The anisotropy of the response is closely related to an anisotropy of the transformation strains due to two basic martensitic transitions β1→β′1 and β1→γ′1 in Cu-based alloys. Calculated transformation strains due to these transitions were compared with the results of compression experiments. The comparison explains well the observed anisotropy of the response of the crystals in thermomechanical loads, in particular, the experimentally observed anisotropy in transformation strains, stresses, hysteresis widths, slopes of transformation lines in stress-temperature diagrams and martensite phases formed under various stress-temperature conditions.