Transpassivity characterization of the alloy UNS N08367 in a chloride-containing solution

We investigate the transpassivity of super-austenitic stainless steel UNS N08367 in 2.5 M LiCl solution by using cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The CPP curve exhibits negative hysteresis, which indicates a transpassive dissolution process instead of pitting corrosion. The transition from the passive region to the transpassive region is characterized by EIS and equivalent circuit analysis. During the transpassive dissolution of the N08367 alloy, two reactions of adsorbed intermediates are dominant, as indicated by the two inductive loops at the transpassive region. The first inductive loop is associated with the faster reaction, i.e., the adsorption of Fe intermediates. This fast reaction is significantly influenced by the preferential dissolution of Fe during the transpassive dissolution. The second inductive loop is correlated with the adsorption of the Cr intermediate. In contrast to Fe, the Cr content on the surface increases in the transpassive region compared with the content in the passive region. The XPS spectra support the time and frequency domain approach for the preferential dissolution, and the dominant species resulted from the interfacial processes at the transpassive region.