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 degrees 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. (c) 2006 Elsevier Ltd. All rights reserved.