Influence of heat treatment on the transformation hysteresis of CuAlNiMnTi shape-memory alloys

Abstract

The electrical resistance method, metallograph analysis, TEM observation and X-ray diffraction analysis have been employed to investigate the influence of heat treatment on the transformation hysteresis (A_f-M_s) of CuAlNiMnTi shape-memory alloys (SMAs). It was found that when the quenching specimens were subjected to ageing treatment, the transformation temperature was decreased and the transformation hysteresis was initially increased, but then tended towards stability; when the quenched specimens were subjected to moderate-temperature treatment at 600‡C, the transformation temperature decreased and the amount of transformation also decreased. The type of thermoelastic martensitic transformation changed from type I and type II and then to type I again, and the transformation hysteresis initially decreasing and then increasing, accompanying the change of the type of thermoelastic martensitic transformation. The reason for this lies in the fact that ageing treatment leads to the precipitation of NiAl-based phase, while moderate-temperature treatment leads to the precipitation of α-phase.