Enhancement of a peak in electrical resistivity of NiTi alloy in early stage of transformation cycles

Abstract

For a better understanding of the transformation behavior on the equiatomic NiTi alloy, the measurement of electrical resistivity was performed in the early stage of transformation cycles, and was compared with the calorimetric measurement. A faint peak in electrical resistivity is observed during the first cooling, at which the temperature is much higher in comparison with the exothermic peak. With increasing transformation cycles, the peak in electrical resistivity is enhanced, at which the temperature is close to the start temperature of the transformation from the intermediate phase to the low-temperature phase. The transformation and the reverse one show a thermal hysteresis of 30 K, and the low-temperature phase is transformed directly to the high-temperature phase, even with increasing transformation cycles. An increase in electrical resistivity with the transformation is detected in the temperature range of the low-temperature phase, which is attributable to the defects induced during the transformation. It is thought on the transformation in the early stage of transformation cycles that the transformation-induced defects play complicated roles such as the electron scattering and the stabilization of the intermediate phase to result in a peak in electrical resistivity.