OXIDE GROWTH AND SPALLING ON FE-CR ALLOYS STUDIED BY HOT STAGE MICROSCOPY

Direct observations by hot stage microscopy of the oxidation of a range of Fe-Cr alloys have shown variations in oxide development. All the oxides formed are Cr2O3 with small amounts of Fe present. Changes in the surface micro-roughness of the oxide have been related to void formation at the metal-oxide interface, and to the negative deviation from parabolic kinetics that has been detected by weight gain measurements during oxidation. The gradual development of extensive oxide ridges over the alloy grain boundaries has illustrated the important influence of these boundaries upon the oxidation of the alloys. The oxide spalling that occurs upon cooling after oxidation has also been directly observed for the same range of Fe-Cr alloys. The spalling is initiated and is always more predominant at the oxide ridges formed at the alloy grain boundaries. The formation of the oxide ridges and the spalling upon cooling increase as the Cr content of the alloys increases and explanations for this are discussed. © 1968 Pergamon Press Ltd.