Effect of ageing treatment on the deformation behaviour of Ti–50.9 at.% Ni Original Research Article

This study investigated the effect of ageing on mechanical behaviour of a Ti–50.9 at.% Ni alloy. The findings enable the construction of a deformation diagram of stress-induced martensitic transformations, depicting the regions and limitations of pseudoelasticity and the shape memory effect of this alloy. It was found that the alloy exhibits pseudoelasticity within a certain temperature and stress window. This window narrows with increasing ageing temperature between 673 and 833 K, with the sample aged at 673 K for 3.6 ks exhibiting the maximum temperature window of ∼40 K for pseudoelasticity. This diagram enables the design of ageing treatment for different thermomechanical behaviour of the alloy. The experimental evidence also indicates that the mechanically induced transformation sequence is different from the thermally induced transformation sequence, implying that the mechanical behaviour of the alloy cannot be predicted from the knowledge of the thermally induced transformations based on the Clausius–Clapeyron correlation between stress and temperature. This study is a sequel to a previous work published in Acta Materialia (2008;56:736). The experimental evidence and the discussions presented in this work are complex. Reading the two articles together is strongly recommended.