Abstract
Two grades of ferritic stainless steel, a bi-stabilized (Ti, Nb) AISI 441 and a stabilized (Ti) AISI 439, were oxidized at 1060°C under simulated process atmosphere for durations between 45 and 1800s. Focused Ion Beam (FIB) coupled with Field Emission Gun and Scanning Electron Microscopy (FEG/SEM) was used to investigate the morphology of the oxide layer. Particularly, metallic protrusions localized at the metal/oxide interface and bulging out through the silica layer were observed. A model based on stress assisted diffusion of oxygen was employed to estimate the effects of the heterogeneous distribution of silica in the oxide. The oxide layer is thought to induce non-uniform nucleation of silica at the metal/oxide interface. Further lateral growth of the silica layer then leads to the formation of metallic protrusions.
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