Transformation-induced plasticity as the origin of serrated flow in an NiTi shape memory alloy

• A highly serrated stress–strain curve is first observed in an NiTi shape memory alloy.
• Transformation-induced plasticity (TRIP) occurs in the serration.
• Latent heat measured by DSC suggests that martensite is partially induced in the serrated flow.

Transformation-induced plasticity was observed in an NiTi shape memory alloy. It was found that the austenite phase of a solutionized 50.5at.% Ni–Ti alloy shows a serrated stress–strain curve in a narrow range of 311–328 K, just below the temperature at which the deformation mechanism of the austenite phase changes from that of stress-induced martensitic transformation in the low temperature ranges to slip at high temperatures (329 K). Microstructure observation and thermal analysis have concluded the simultaneous occurrence of the two deformation mechanisms in the serrated flow. The interaction between the martensitic transformation and slip was investigated.