[Truncated] This thesis reports on a study of the shape memory behaviour in a Ti-50.2%Ni alloy. The study consists of mainly three parts, (i) transformation behaviour, (ii) mechanical behaviour and (iii) two-way memory training. The transformation behaviour was studied with respect to the effect of heat treatment after cold work. Experiments were carried out using D S C and T E M methods. It is found that a NiTi alloy m a y exhibit two different transformation sequences, P <-> M or P —» R —> M -» P, according to the annealing temperature being above or below a critical temperature. The critical temperature is closely related to recrystallisation. Insitu observation of the transformations was carried out on a Philips 430 T E M. Structures such as polygonal grains of parent phase with twin-like parallel streaks, martensite with stripe patterns and plate martensite, and order-disorder domains were examined. The 1/3(110) and 1/3(111) diffraction spots, the characteristic reflections of the R phase, were found in specimens annealed even at temperatures above the critical annealing temperature, indicating the thin film effect on transformation behaviour. The 1/3 spots were observed to intensify with decreasing temperature.
|Qualification||Doctor of Philosophy|
|Publication status||Unpublished - 1990|