INTERNAL OXIDATION OF Fe_3Al DURING HIGH TEMPERATURE OXIDATION

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The oxidation behavior of Fe_3Al at 1 000 ℃ in air was studied by thermobalance, scanning electron microscope (SEM) and X-ray diffraction (XRD). It was found that the oxidation kinetics approximately follows the parabolic law; the oxide scale consists of Al_2O_3 and a little amount of Fe_2O_3; and there occurs transgranular internal oxidation. Based on the analyses of the oxide scale and the matrix, an internal oxidation model was proposed, which considers the effect of the long-range ordered structure of Fe_3Al on its hightemperature oxidation. The longrange ordered structure reduces the activity of Al in Fe_3Al, thus reducing the diffusion coefficient of Al in the matrix. Consequently, in the oxidation process, the matrix surface will be seriously depleted in Al and then there occurs internal oxidation.