Oxidation behaviour of Fe40Al alloy strip

The oxidation behaviour of FeAl foils of 200 μm thickness was investigated in air at 900 and 1100°C for up to 1000 h exposure. Microstructural examination reveals the formation of an even alumina scale with small islands of (Fe,Al)-oxides which may be associated with chemical heterogeneities reaching the surface. No cracking or spallation was found. At the lowest temperature the scale is decorated with small platelets associated with metastable θ-alumina which transforms to the more stable α-alumina with progressing oxidation. At the highest temperature, metastable phases were not observed. For the longest exposure, however, whiskers of alumina on the top of the scale were found to develop with progressing oxidation. The observation of significant differences between the oxidation behaviour of thin foils and thick materials regarding scale spallation is related to the relaxation of growth stresses in the scale by spontaneous deformation of the substrate by creep.