Characterization of transformation behavior in NiTi(Si)

Abstract

For a better understanding of the transformation behavior in NiTi alloy containing silicon, the electrical resistivity and the thermal property in NiTi and NiTi(Si) were precisely measured by a four-probe potentiometric method and differential scanning calorimetry, respectively. The transformation behavior depends on the thermal cycles with the repetition of the transformation, and the thermal cycles tend to stabilize the intermediate phase during cooling because of the enhancement of a peak in the electrical resistivity. The peak in the resistivity of NiTi with increasing thermal cycles is markedly enhanced in comparison with NiTi(Si). The reverse transformation during heating remains a one-stage transformation from the low-temperature phase to the high-temperature phase in both NiTi and NiTi(Si). Although a peak in the resistivity during heating is detected in NiTi(Si), it is evaluated to be a seeming peak because the resistivity of the low-temperature phase is larger than that of the high-temperature phase near the reverse transformation temperature. The increase in the resistivity due to the transformation-induced defects is very large for the transformation of NiTi(Si), and NiTi(Si) is useful for examining the formation of defects introduced by a repetition of the transformation. It proved necessary to measure not only the electrical resistivity but also the thermal property in order to characterize the transformation behavior and the effect of the electron scattering, which are altered by an additional element.