Effect of Ni content on the transformation behavior and mechanical property of NiTi shape memory alloys fabricated by laser powder bed fusion

Abstract

In this study, three NiTi shape memory alloys with different Ni atomic percentage (50.73, 50.93 and 51.27 at%) were fabricated by laser powder bed fusion (L-PBF). The effect of Ni content on phase transformation temperature, phase composition, microstructure, mechanical properties and deformation recovery phenomenon of NiTi alloy were systematically investigated. The results indicated that the Ni content of L-PBF NiTi alloy affected Ms temperature and further affected phase composition. According to the effect of Ni contents on phase transition temperatures, a relationship between them was fitted. Subsequently, an equation defining the atomic percentage phase transition temperature is proposed. The effect of Ni content on grain orientation, texture and grain size was limited, but it had an effect on hardness and compression performance. L-PBF NiTi sample displayed shape memory effect with the lower Ni content (50.73 at%), however, showed superelasticity phenomenon with the higher Ni content (50.93 and 51.27 at%). Therefore, transformation temperature and deformation recovery phenomenon of L-PBF NiTi alloy could be tailored by adjusting Ni content to achieve special applications in the future.