Effects of aging on stress-induced martensitic transformation in ductile Cu-Al-Mn-based shape memory alloys

Effects of aging at 473-573 K on stress-induced martensitic transformation for textured Cu(71.9)Al(16.6)Mn(9.3)Ni(2)B(0.2) and random-textured Cu(72.1)Al(16.9)Mn(0.5)Co(0.5) shape memory alloy (SMA) wires with a large relative grain size d/D = 6 were investigated by cyclic tensile testing at room temperature, where d and D indicate mean grain size and wire diameter, respectively. The random-textured Cu(72.1)Al(16.9)Ma(10.5)Co(0.5) wire cannot be uniformly deformed and the ductility is drastically reduced by aging treatment. On the other hand, in the textured Cu(71.9)Al(16.6)Mn(9.3)Ni(2)B(0.2) SMA wire, the critical stress for martensitic transformation sigma(t) and the tensile strength sigma(f) are increased by aging without the associated loss of superelasticity (SE). Even in textured wire with a high sigma(t) of over 750 MPa, an excellent SE strain of about 6% can be obtained due to the formation of a fine bainite phase. Moreover, it was confirmed by in situ observation that stress-induced martensite plates grow, accompanying distortion of the bainite plates. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.