Martensitic transformations in [001] CuAlZnMn single crystals

Thermoelastic martensitic transformations exhibited by [001] oriented CuAlZnMn shape memory alloy single crystals were investigated by tension/compression thermomechanical experiments. Thermal cycling tests at constant applied stress, mechanical cyclin tests at constant temperature as well as complex thermomechanical tests were performed to determine the transformation conditions in a wide range of applied stresses and temperatures. The martensitic phase induced typically under tensile stress (beta(1)-18R monoclinic structure) was different from that induced by compressive stress (gamma(1)-2H orthorhombic structure) and the related tension/compression asymmetries were investigated in detail. Particularly, the wide thermal as well as stress hysteresis due to the beta(1)-->gamma(1) transformation involving large compressive strains is a peculiar Feature of the CuAlZnMn alloy and probably an origin of the wide hysteresis effect exhibited by the polycrystalline CuAlZnMn shape memory alloy. A mechanism based on the non-equivalent crystallographic transformation paths of the forward and reverse beta(1)<->gamma(1) martensitic transformation was proposed to explain this phenomenon. (C) 1998 Acta Metallurgica Inc.