Air oxidation of a Zr58Cu22Al12Fe8 bulk metallic glass at 350-550°C

The oxidation behavior of the Zr58Cu22Al12Fe8 bulk metallic glasses (ZC4-BMG) was studied over the temperature range of 350-550 degrees C in dry air. The oxidation kinetics of the ZC4-BMG generally follow a multi-stage parabolic-rate law, and the steady-state parabolic-rate constants (k(p) values) increased with increasing the temperature when it is below the glass transition temperature (T-g = 413.3 degrees C). Conversely, the k(p) values were nearly identical from 400 to 550 degrees C. The scales formed on ZC4-BMG were composed mostly of tetragonal-ZrO2 (t-ZrO2) and minor amounts of Al2O3 and monoclinic-ZrO2 (m-ZrO2). The amounts of both Al2O3 and m-ZrO2 increased with increasing the temperature. In addition, the amorphous substrate remained unchanged after the oxidation for 36 h at T <= 375 degrees C. However, it transformed into different crystalline phases at higher temperatures, which are strongly dependent on the temperature and duration of time. (C) 2009 Published by Elsevier B.V.