Effect of ferroelastic cycling via martensite reorientation on the transformation behaviour of nickel-titanium

Abstract

It has been observed that deformation stabilises martensite in a number of shape memory alloys, as evidenced by the increase of the critical temperature for the reverse transformation of the deformed martensite as compared to undeformed martensite. Some hypotheses have been proposed in the literature to explain this phenomenon, including the pinning effect of deformation-induced defects and the release of internal elastic energy stored in thermal martensite. This study continues the experimental work by studying the effect of ferroelastic cycling via martensite reorientation on the transformation behaviour of a binary near-eqniatomic NiTi, with the aim to provide further experimental evidence for the clarification of the mechanisms responsible for this effect. It was observed that the critical temperature and the heat of the reverse transformation of oriented martensite increased progressively with deformation cycles, although the limits of the deformation cycles remained unchanged.