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

Abstract

Effects of aging at 473–573 K on stress-induced martensitic transformation for textured Cu 71.9Al 16.6Mn 9.3Ni 2B 0.2 and random-textured Cu 72.1Al 16.9Mn 10.5Co 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 72.1Al 16.9Mn 10.5Co 0.5 wire cannot be uniformly deformed and the ductility is drastically reduced by aging treatment. On the other hand, in the textured Cu 71.9Al 16.6Mn 9.3Ni 2B 0.2 SMA wire, the critical stress for martensitic transformation σ t and the tensile strength σ f are increased by aging without the associated loss of superelasticity (SE). Even in textured wire with a high σ 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.