A thin salt film, typically a few micrometers thick, can form at the interface between the active metal surface in a pit and the pit electrolyte. Salt film precipitation on the pit surface can occur when the local concentration of metal cations at the surface surpasses the solubility limit. Salt films are of critical importance because they can either stabilize pit growth or facilitate repassivation. Therefore, elucidating their mechanisms of formation, structure, and properties is essential for mitigating localized corrosion. In this work, one-dimensional (1D) pit tests were combined with flash freezing and cryogenic-based electron microscopy techniques to examine the morphological and chemical characteristics of salt films formed on Fe- and Ni-based alloys and correlate these features with the repassivation behavior. Results show that repassivation under a salt film can occur for SS304 under potentiostatic conditions, both during isothermal holds and during decreasing temperature scans. In contrast, Alloy 600 does not repassivate under the same conditions, suggesting that repassivation under salt-film is less favorable for this alloy. Cryogenic characterization reveals distinct characteristics in salt film structure and composition, which may explain the contrasting behaviors of Fe- and Ni-based alloys. Overall, these findings provide new insight into how salt-film properties influence pit stability and repassivation processes in Fe-Ni-Cr alloys.
