Phase transformations, detwinning and superelasticity of shape-memory NiTi from MEAM with practical capability

Abstract

We present a second nearest-neighbor interatomic potential improved with the mechanical properties of the bulk B2 and B19’ phases in shape-memory NiTi alloys. The potential correctly predicts the phase transformations known so far in the temperature-stress-strain diagram of equiatomic NiTi. Bulk materials show the perfect reversibility between B2 and B19’ over many thermal cycles. The perfect reversibility showing superelasticity is also observed in the nanopillars under both tensile and compressive loadings. Most important, twinning naturally occurs in the nanopillars upon cooling below the transition temperature, and the subsequent tensile loading removes twinning irreversibly. We find that a potential based on accurate mechanics warrants the mechanical and thermomechanical behaviors in shape-memory NiTi necessary for a practical use.