Age-induced four-stage transformation in Ni-rich NiTi shape memory alloys

A four-stage transformation has been observed in an aged Ti–50.7 at.%Ni shape memory alloy by differential scanning calorimetry (DSC). Such phenomenon is able to occur in the alloys with compositions around 50.7 at.%Ni by aging at 673 K. The multi-stage transformation behavior observed in this study is attributed to the complex microstructural evolution, i.e., formation of large-scale and small-scale heterogeneities which induced various stress fields and affected the phase transformation sequence.