The isothermal oxidation behavior of Fe-20 Cr alloys with additions of 0, 0.2, 0.5, 0.7, 1.0 and 1.3 wt%La was studied in air at 1273 K by weight gain measurements, scanning electron microscopy, X-ray diffraction and electron probe microanalysis.
The alloys with additions of 0.2%La or less exhibited severe oxidation with the formation of thick stratified scales of α-Fe
2O
3 and spinel oxide. On the other hand, the alloys with additions of 0.5%La or more exhibited good oxidation resistance. The formation of the protective La
2O
3 or LaCrO
3 layer at the scale base, the convoluted alloy/oxide interface and the enhanced diffusion of any particular element were not observed in this study, although these had been proposed to be main mechanisms by which the improvement of oxidation resistance was enhanced by the rare earth additions. Since additions of 0.5%La or more completely suppressed the formation of the iron oxides and the Cr
2O
3 scale was maintained stably during the oxidation period, the oxidation behavior of Fe-20 Cr binary alloy and the affect of La addition were discussed thermochemically.
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