Competitive Effect of Water Vapor and Oxygen on the Oxidation of Fe–5 wt.% Al Alloy at 1073 K

Abstract

The effect of oxygen on the oxidation of Fe–5wt.% Al alloy was investigated at 1073 K in N2–12.2 vol.% H2O, O2–12.2 vol.% H2O, and N2–O2–12.2 vol.% H2O with various amounts of oxygen. The results showed S-shaped oxidation curves that consisted of three stages: slow-incubation, rapid transition, and relatively slow oxidation. The amount of oxidation increased with increasing oxygen contents up to 0.9 vol.% O2 and then rapidly decreased. On the oxygen-rich side, a slow incubation oxidation stage was observed and its duration increased with increasing oxygen content. The extent of oxidation decreased gradually with decreasing oxygen content from the critical value and the incubation period disappeared. In the transient period, Fe2O3 was formed on the lean oxygen-content side and elongated voids were formed in the outer Fe3O4 and FeO layer. It was suggested that the differences in the morphology of Fe2O3 formed on the surface affected by the dissociation and gas-transport process due to differences in oxygen partial pressure at the gas–scale interface.