Nanoscale early oxidation mechanisms of model FeCrNi austenitic stainless steel surfaces at room temperature

Scanning tunneling microscopy was applied to investigate the topographical and structural alterations at small spatial and temporal scales of a model 304 austenitic stainless steel surface resulting from ultra-low exposures to gaseous oxygen at room temperature. The 2D nucleation and growth mechanisms were observed until surface saturation by a fully covering and nanogranular Cr(III)-enriched oxide film. Local supply of metallic Fe and Cr for oxide nucleation and growth is concluded to be at the origin of heterogeneity developed in the oxide film at the nanoscale. This work provides nanoscale understanding basis for composition and morphology tuning of Cr-enriched oxide film for improved local stability of passivity