Passive Films Formed on Fe- and Ni-Based Alloys in an Alkaline Medium: An Insight into Complementarities between Electrochemical Techniques and Near-Field Microscopies (AFM/SKPFM)

Abstract

This study investigates the natural passivation process of two types of stainless steels (AISI 316 and AISI 304) and a nickel-based alloy (Inconel 600) as a function of immersion time in an alkaline medium. As shown by Atomic Force Microscopy (AFM), the oxide film growth on each substrate is only influenced by trenches formed during the polishing step and does not depend on the chemical composition. The evolution of EIS measurements is explained by this growth mode. After 3 days of immersion, the formed film constitutes a protective barrier against alloy dissolution, as shown by Scanning Kelvin Probe Microscopy (SKPFM).