Thermal analysis of the effect of aging on the transformation behaviour of Ti–50.9at.% Ni

This study investigated the effects of aging on the transformation behaviour of a Ti–50.9at.% Ni alloy by means of differential scanning calorimetry. It was found that aging at 673 K induced complex transformation behaviour, involving the R-phase and multiple-stage martensitic transformations. The martensitic transformations were analysed in details in partial transformation cycles. It was evident that the martensitic transformation from the R-phase occurred in a stable manner progressively over a wide temperature range. These evidences appear to support the precipitate inhomogeneity hypothesis for the explanation of multiple-stage martensitic transformations and disprove the hypothesis that martensitic transformations in near-equiatomic NiTi occur in burst manner.