A one-cycle training technique for copper-based shape memory alloys

Shape memory alloys have been used in the industrial and medical fields due to their shape memory effect (SME), pseudoelasticity and two-way shape memory effect (TWSME). With TWSME, the shape memory alloy (SMA) can changes its shape during heating and recover its shape during cooling. This recoverable property can be thermally cycled over 105 times, but TWSME is not an intrinsic property of shape memory alloys: it should be trained by multiple thermomechanical cycling. The present authors have developed a one-cycle training technique to obtain TWSME for Cu-based alloys. This method is usually called the stabilized stress-induced martensite (SSIM) training method. With the SSIM training in Cu-based alloys, many small γ precipitates were induced with a large strain field oriented in a same direction in the austenite. It was considered that these oriented γ precipitates in the austenite contribute their strain field to thermoelastic martensite transformation during cooling. When the alloy is heated again, during reverse transformation the strain field around the γ precipitates can be recovered again. In this way, with only one-cycle training, the Cu-based SMA can obtain TWSME.