Transformation behaviour with thermal cycling in NiTi alloys

The transformation behaviour of NiTi alloys were investigated by differential scanning calorimetry in order to reveal the effects of thermal cycles with the repetition of the transformation. The thermal cycles tend to lower the transformation temperature between the high and low temperature phases and to stabilize the intermediate phase during cooling to result in a two-stage transformation, while the reverse transformation during heating remains a one-stage transformation. Because these effects of the thermal cycles depend on the composition and the deformation, it is thought that defects play an intrinsic role in the complicated behaviour of NiTi alloys.