Growth mechanism of Al2O3 scales developed on Fe Cr Al alloys

Abstract

By combining classical techniques used for oxidation studies, electrochemical measurements on the oxide scale and 18O profilings by using the 18O(p, α) 15N reaction, it was possible to obtain reliable data on the growth mechanisms of alumina scales developed at 1082°C on three Fe Cr Al alloys differing by their impurity amount. It was shown that aluminum diffusion through the scale is the major material transport mechanism during oxidation, resulting in an outside scale growth. Nevertheless, carbon and other impurities enhance the oxygen inward diffusion and improve the scale adherence. Alumina scales behave as a mixed ionic and electronic conductor, but the incorporated impurities decrease the values of ti, σi and kp, thus accounting for a slower oxidation rate in an industrial alloy than in a high purity one. © 1987.