In-situ phase transformation and corrosion behavior of TiNi via LPBF

As well known, shape memory effect of TiNi alloy is driven by phase transition under stress or temperature variation. Corrosion behavior of the TiNi component particularly that produced by additive manufacturing associated with phase transition is still a blind point. In this work, the control of B2/B19′ phase composition in the NiTi component is realized via LPBF. Subsequently, electrochemical testing was carried out to evaluate the corrosion resistance of NiTi alloys. The results show that the as-printed sample exhibits a better corrosion resistance than the ingot sample. Furthermore, the as-printed sample with full B2 phase yields a much stronger pitting corrosion resistance than that with a mixed B2/B19′ phase. Based on the first principle calculations, it is found that the stability of passive film on B19′ phase is slightly weaker than that on B2 phase. Moreover, Tof-SIM analysis revealed that the passive film obtained from component surface with mixed B2/B19′ phase is irregular, where pitting corrosion tended to initiate. This work is believed to serve as a reference for the process optimization of additive manufacturing NiTi shape memory alloys. • This paper systematically researches single/mixed phase composition of TiNi alloy prepare by LPBF. • Phase composition control of TiNi alloy were realized by laser parameters optimization in LPBF. • Corrosion behavior of TiNi alloy with different phase compositions was characterized. • Potential of B2 and B19′ phase was tested and calculated by AFM and First-principles calculations. • Pitting trend to occur on irregular passive film surface of TiNi alloy with mixed B2/B19′.