Vacancies in NiTi shape memory alloys

Abstract

NiTi shape memory alloys were examined with a mono-energetic positron beam. The thermal vacancy formation enthalpy was found to be 0.77±0.08 eV. Upon heating NiTi the martensitic S value is retained to temperatures significantly above the phase transition temperature and then decreases towards the austenitic value only gradually. In contrast upon cooling, a narrow transition region at 81.5±1.5 °C is observed. The magnitude of the transition strongly depends on the annealing temperature. © Published under licence by IOP Publishing Ltd.