Synergistic roles of Ti4Ni2Ox nanoprecipitates and homogeneous micro-strain in the pitting resistance of LPBF dual-phase NiTi alloys

Authors:
Preprint
Publisher website
Google Scholar
Abstract
The corrosion resistant of Laser Powder Bed Fusion (LPBF) dual-phase NiTi alloys remains controversial, and the underlying mechanisms are not fully understood. In this study, a tailored LPBF combined with annealing strategy was employed to introduce martensite-rich (~46.5% martensite) dual-phase NiTi alloys (HT500) with homogeneous micro-strain. Despite rapid initial anodic dissolution, the HT500 sample exhibits pronounced repassivation, resulting in an extended passive region of approximately 1600 mV and only a limited number of shallow pits. This passive region is substantially wider than those reported for predominantly austenitic LPBF NiTi alloys (typically ~300 mV) and commercial wrought NiTi alloys (typically ~700 mV). It can be attributed to the synergistic effects of the evolution of Ti4Ni2Ox nanoprecipitates and the homogeneous micro-strain distribution. The net-like and ellipsoidal Ti4Ni2Ox nanoprecipitates initially dominate the local micro-galvanic coupling due to high micro-galvanic driving force (360 mV), resulting in a rapid increase in anodic current density. Subsequently, their partial detachment during polarization progressively weakens the micro-galvanic driving force (160 mV) and suppresses localized corrosion susceptibility. Meanwhile, continuous regeneration of the passive film promotes current stabilization, while the homogeneous micro-strain distribution suppresses localized corrosion and limits pit propagation. These findings provide new insight into the superior pitting resistance of martensite-rich dual-phase NiTi alloys over predominantly austenitic counterparts, emphasizing the importance of nanoprecipitates and micro-strain beyond phase constitution alone.

This publication has 21 references indexed in Scilit: