Growth mechanism of and residual stresses in scales on oxide-dispersion-strengthened Fe20Cr5Al + Y2O3 alumina former oxidized at 100°C

Evolution of the oxide scale growing at 1000 degrees C as a result of up to 1-hour exposures in air on Fe20Cr5Al + Y2O3 ODS-type alloy (MA956). was studied using an approach which enabled getting insight into its consecutive stages in terms of the phase and chemical composition, growth mechanism and morphology of the oxide layer. Only alpha-Al2O3 oxide was found in the scale for oxidation exposures more prolonged than 2 min. 45 sec. In the case of 2 mm. 45 sec oxidation period, a small amount of transient oxide, theta-Al2O3 was detected. Although relatively flat and uniform scale developed under all the studied conditions some Ti-rich oxide particles appear at its surface. Inward growth mechanism predominated at very early oxidation stages. Only for 2 min. 45 sec exposure the oxide was mainly formed near the scale-gas interface rather than in deeper parts of the scale. The residual stresses did not exceed 2.5 GPa and increased by ca. 50% as the exposure proceeded.