Possible scaling modes in high-temperature oxidation of two-phase binary alloys. II: Low oxidant pressures

The main possible modes of the high-temperature corrosion of binary two-phase alloys by a single oxidant under gas-phase pressures sufficient to corrode only the most-reactive alloy component are examined to compare their behavior with that of single-phase alloys. In the absence of important diffusion processes of the metal components in the alloy, the scale structures expected are different from those typical of single-phase alloys. Moreover, when diffusion in the alloy becomes important, these systems may develop an outer single-phase layer depleted in the most-reactive component, which may lead to different possible scale structures. The conditions for the transition between the various oxidation modes as well as the effect of the various parameters of kinetic, thermodynamic, and structural nature over the corrosion behavior of two-phase alloys are also examined.