Neutron diffraction study on strain rate dependent mechanical response in superelastic NiTi alloy: Bulk structural evolution and constitutive model

As expanded service environments, it is necessary to investigate the deformation behavior of NiTi shape memory alloy under dynamic and impact loadings. In this paper, we study bulk structural responses of a superelastic NiTi alloy in strain rates from 10 ⁻⁵ s ⁻¹ to 3 × 10 ³ s ⁻¹ by neutron diffraction method. The objective is to quantify structural parameters of NiTi alloy at various strain rates, and compare the differences in deformation mechanisms. Further, we derive a phenomenological model based on experimental cognition to describe the strain rate dependent mechanical responses. The results demonstrate that impact loading obviously prevents stress-induced martensitic transformation in NiTi alloy. The austenite parent phase undergoes more significant slip deformation during high-speed deformation, which is hardly observed in quasi-static compression. Meanwhile, the austenitic crystal orientation during impact loading is not essentially different from that of quasi-static condition. Through an estimation of temperature effect, the strain rate effect is caused by adiabatic temperature rise. In validation of the phenomenological model, it is proved that the model well reproduces not only stress-strain curves but also structural parameters obtained from the neutron diffraction experiments.