The effects of Ti3Ni4 precipitates on the R-phase transformation

Abstract

TiNi is an important alloy for its shape memory effect. It is known that both the martensite and the R-phase transformations are responsible for the shape memory effect. There are several kinds of precipitate in near equal atomic, Ni-rich TiNi alloy, amongst which Ti[sub 3]Ni[sub 4] precipitates most strongly influence the R-phase and martensite transformations. Use of constrained aging can promote the all-around shape memory effect (ARSME) because the stress fields generated by the Ti[sub 3]Ni[sub 4] precipitates is thought to introduce univariant R-phase and martensite transformation. A number of studies have been performed to understand the effects of the precipitates, but disagreement still exists. Xie et al. showed that the morphology of the R-phase is dependent on the dispersion of the precipitates. In specimens with coarse precipitates, the R-phase has a needle-like domain structure, while in specimens with fine dispersed precipitates a 'basket weave-like structure', is observed after the R-phase transition. Conversely, Nishida et al. report that the appearance of the R-phase transformation is attributable to the formation of precipitates, while the presence of precipitates and the difference in precipitate distribution does not influence the crystallographic and morphological nature of the R-phase transformation. The purpose of this work ismore » to systematically study the effect of Ti[sub 3]Ni[sub 4] precipitate on phase transformation. Here the authors report a preliminary investigation of this work.« less