Air oxidation of an Fe₇₂B₂₂Y₆ bulk amorphous alloy at 600-700 °C

The oxidation behavior of the Fe₇₂B₂₂Y₆ bulk metallic glass and its crystalline counterpart was studied over the temperature range of 600-700 °C in dry air. The results showed that the oxidation kinetics of both glassy and crystalline alloys in general follow a parabolic rate law although a two-stage kinetics was noted at 700 °C for the glassy alloy. The oxidation rates of the two alloys increased with increasing temperature, and the parabolic rate constants of the glassy alloy are much lower than those of the crystalline counterpart. The scales formed on the glassy alloy consisted mainly of boron oxide (B₂O₃) and minor amounts of iron oxides (Fe₃O₄/FeO). Conversely, duplex scales formed on the crystalline counterpart were composed of an outer layer of Fe₂O₃ and an inner layer of Fe₃O₄-YBO₃ mixture. The formation of B₂O₃ is responsible for the reduced oxidation rates of the glassy alloy as compared to those of crystalline counterpart.