The oxidation behavior of the Cu 47.5 Zr 47.5 Al 5 (Cu3) and Cu 47 Ti 34 Zr 11 Ni 8 (Cu4) bulk metallic glasses (BMGs) was studied over the temperature range of 400°C to 500°C in dry air. The oxidation kinetics of both alloys generally followed a multistage parabolic-rate law, and the steady-state parabolic-rate constants (k p values) fluctuated with temperature for the Cu3 BMG, but increased with increasing temperature for the Cu4 BMG. The scales formed on the BMGs were strongly dependent on the temperature and alloy composition, and were composed primarily of tetragonal-ZrO 2 (t-ZrO 2 ) and minor amounts of Al 2 O 3 , Cu 2 O, and CuO at 400°C for the Cu3 BMG, while the monoclinic-ZrO 2 (m-ZrO 2 ) phase is present at T ‡ 425°C, and the Cu 2 O phase is absent at 500°C. Conversely, the scales formed on the Cu4 BMG consisted exclusively of CuO at 400°C, while minor amounts of t-ZrO 2 , TiO 2 , and ZrTiO 4 formed at 425°C to 450°C, and TiO was also detected at higher temperatures. It was found that both amorphous Cu3 and Cu4 substrates transformed into different crystalline phases, and were strongly dependent on temperature and duration of time.

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The oxidation behavior of a Cu 60 Hf 25 Ti 15 bulk metallic glass was studied over the temperature range of 375-520°C in dry air. The oxidation kinetics of the amorphous alloy generally followed the parabolic law at all temperatures, with an oxidation rate increasing with temperature. The oxidation rates of the amorphous alloy were much higher than those of polycrystalline pure-Cu, implying that the additions of Hf and Ti accelerated the oxidation reaction. The composition of the scales formed on the amorphous alloy was strongly temperature-dependent, since they consisted mostly of Cu 4 O 3 and CuO with minor amounts of HfO 2 at T 450°C, while mostly CuO with minor amounts of HfO 2 and Cu 2 TiO 3 were detected at higher temperatures. In addition, nanocrystalline Cu 51 Hf 14 and Cu 3 Ti 2 phases were detected on the substrate after oxidation at T ! 450°C, indicating the occurrence of phase transformation.

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