Localized Plastic Deformation of Superelastic NiTi Wires in Tension

Abstract Tensile deformation of superelastic NiTi shape memory alloy wires at temperatures above austenite finish temperature proceeds via stress-induced martensitic transformation followed by plastic oriented martensite. While tends to proceed in localized manner, martensite is considered be homogeneous. In this work, we have investigated strain localization patterns tensile tests on deformed until fracture wide range from 10 400 °C using situ digital image correlation analysis local strains and analyzed lattice defects created during the TEM. We found that can either homogeneous or localized, depending yield stress hardening rate (on Considere criterion for stability deformation). Plastic peculiar mode involving combination twinning dislocation-based kinking. Strain takes form necking leading wire 13–15% propagation macroscopic band fronts constant stress. Regardless reach ~ 50%. within propagating front as large 40% was observed test having specific microstructures (grain size 230 nm) a narrow (~ 10–60 °C).