Oxidation behavior of ODS Fe-Cr-Al alloys:: Aluminum depletion and lifetime

The oxidation kinetics of two ODS Fe-Cr-Al alloys, PM 2000 and MA 956, were studied in oxygen and in air under isothermal conditions from 1000 to 1300degrees C. They both form an alpha-alumina scale and have good oxidation resistance, without any mass loss. Although the aluminum content in these alloys is higher than the minimum Al content necessary to ensure the growth of a continuous alumina scale, an aluminum depletion occurred in the substrate. This depletion allows the determination of aluminum diffusion coefficients in the ODS alloy. This method is very original and interesting as no Al-stable isotope is available. Moreover, the evolution of the aluminum concentration in the substrate allows one to determine the lifetime of these alloys: indeed, when the aluminum content decreases and becomes lower than a critical value, alumina can no longer form, and less-stable oxides grow very rapidly compared to alumina.