Effect of ageing treatment on the transformation behaviour of Ti–50.9 at.% Ni alloy

This study investigated the effect of ageing on the transformation behaviour of a Ti–50.9 at.% Ni alloy. Ageing at below 573 K was found to suppress the original A ↔ M transformation. This phenomenon has not been recognized in the literature. The effect is ascribed to the lowering of B2 ordering of the matrix caused by the formation of GP zones as a pre-phenomenon for precipitation. Ageing at between 573 and 813 K resulted in complex multiple-stream transformations. These complex transformation behaviours are attributed to long-range heterogeneity of precipitation structure between grain boundaries and grain interior, and short-range heterogeneity caused by partial dissolution of coherent precipitates and formation of incoherent precipitates. Ageing at above 833 K led to a single-stage A ↔ M transformation, which indicates total dissolution of coherent Ti3Ni4.