Competitive effect of water vapor and oxygen on the oxidation of Fe-5 wt.%Al alloy at 1073 K

The effect of oxygen on the oxidation of Fe-5wt. % Al alloy was investigate d at 1073 K in N-2-12.2 vol.% H2O, O-2-12.2 vol.%H2O, and N-2-O-2-12.2 vol. %H2O with various amounts of oxygen, The results showed S-shaped oxidation curves that consisted of three stages: slow-incubation, rapid transition, a nd relatively slow oxidation. The amount of oxidation increased with increa sing oxygen contents up to 0-9 vol.%O-2 and then rapidly decreased. On the oxygen-rich side, a slow incubation oxidation stage was observed and its du ration increased with increasing oxygen content. The extent of oxidation de creased gradually with decreasing oxygen content from the critical value an d the incubation period disappeared. In the transient period, Fe2O3 was for med 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 mo rphology, of Fe2O3 formed on the surface affected by the dissociation and g as-transport process due to differences in oxygen partial pressure at the g as-scale interface.