Superelasticity and corrosion resistance of NiTi shape memory alloy in 10 wt% H2SO4 solution: The role of heat treatment

Abstract

This study examines the comprehensive effects of heat treatment processes on the microstructure, mechanical attributes, and corrosion resistance of NiTi shape memory alloys in acidic solutions. Through meticulous experimentation and analysis, several key findings were uncovered: Heat treatment enhances the volume fraction of the B19' martensite phase and refines the distribution morphology of Ti-C carbides. Such microstructural alterations yield a moderate enhancement in alloy strength, though there is a slight decline in superelasticity performance. Heat treatment profoundly elevates the corrosion resistance of NiTi shape memory alloys in dilute sulfuric acid solutions. This is evidenced by a notable rise in corrosion potential, a marked reduction in corrosion current density, an increase in charge transfer resistance, and an elevation in the flat band potential of the passivation film on the alloy surface, accompanied by a decrease in carrier concentration. These improvements in corrosion resistance largely stem from the fact that heat treatment markedly optimizes the alloy's microstructure and compositional uniformity. Consequently, this enhances the consistency and stability of the passivation film on the alloy's surface, ensuring more reliable performance of NiTi shape memory alloys in acidic conditions.