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).

This study presents a combined electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM) and Scanning Kelvin Probe Force Microscopy(SKPFM) investigation on the natural passivation process of stainless steels (AISI 316 and AISI 304) and nickel-based alloy (INCONEL 600) as a function of immersion time in an alkaline medium (pH = 13). EIS measurements show an increase in the resistance of the film with increasing immersion time in the electrolyte. After 3 days of immersion, for the three alloys, the films formed constitute an effective barrier to the dissolution of the alloys as shown by AFM and SKPFM. The oxide film growth on each substrates is only influenced by trenches formed during the polishing step and don’t depend on the chemical composition.