Rate dependence of deformation mechanisms in a shape memory alloy

The rate-dependent tensile deformations of twinned martensitic NiTi shape memory alloy (SMA) are studied for strain rates as high as 300s(-1). The results show that the stress plateau associated with the martensite detwinning process still exists under high-strain-rate deformations. The results further suggest that the detwinning process taking place at the initial stage of the tension deformation is not very sensitive to the strain rate at least within the studied range (10(-3)-3 x 10(2) s(-1)). Beyond the stress-plateau region where dislocation mechanisms are expected to dominate the deformation processes, the stress level increases more strongly with increasing strain rate. The transformation characteristics and shape recovery processes of the dynamically deformed samples provide further evidence that the detwinning process is well developed in the NiTi SMA under dynamic tension deformation.