Effect of microstructure on the passive behavior of selective laser melting-fabricated Hastelloy X in NaNO3 solution

The electrochemical dissolution characteristics of nickel-based alloys produced by selective laser melting (SLM) have received considerable attention in electrochemical machining (ECM). However, the passive behavior of Hastelloy X (HX) during ECM has not been systematically investigated so far. This study aimed to investigate the effect of microstructures on the passive behavior of SLM-fabricated HX, and compare it with that of wrought HX. The findings indicated that the XOY plane (perpendicular to build direction) with the refined microstructure exhibited a superior corrosion resistance. Compared to the wrought plane (the cross-sectional plane), the finer grain size, denser sub-grain boundaries, and dislocations all contributed to the formation of a more stable and thicker passivation film on the XOY plane of SLM HX in 10 wt% NaNO3 solution. An analysis of the Auger electron spectroscopy and X-ray photoelectron spectroscopy measurement results showed that a comparatively thick outer layer existed in the passivation film.