The oxidation behavior of an Fe61B15Zr8Mo7Co5Y2Cr2 bulk metallic glass at 550-700 °C

The oxidation behavior of an Fe61B15Zr8Mo7Co5Y2Cr2 bulk metallic glass (Fe7-BMG) and its crystalline counterpart (XFe7) was studied over the temperature range of 550-700 degrees C in dry air. In general, the results showed that the oxidation kinetics of the Fe7-BMG and XFe7 alloys followed a parabolic-rate law, with their oxidation rates increasing with temperature. It was found that the oxidation rate constants (k(p) values) of the Fe7-BMG are slightly higher than those of XFe7, indicating that the amorphous alloy underwent a fast oxidation reaction. The scale formed on the Fe7-BMG at 550 degrees C for 48 h was thin and heterophasic mixture of iron oxides (Fe2O3/Fe3O4) and tetragonal-ZrO2 (t-ZrO2). At higher temperatures (T >= 600 degrees C), duplex scales formed on the glassy alloy consisted of an outer layer of iron oxides (Fe2O3/Fe3O4) and minor amounts of B2O3, and of a heterophasic inner layer of mostly t-ZrO2 intermixed with non-oxidized Fe3B, FeCo, and ZrB12. The formation of the crystalline intermetallics indicated the occurrence of the substrate crystallization at the temperature range of interest. (C) 2008 Published by Elsevier Ltd.