The oxidation behavior of a novel Ni-free Zr-Cu-based bulk metallic glass composite in the supercooled liquid and crystallization states

The oxidation behavior of a novel Ni-free (Zr₄₈Cu ₃₂Al₈Ag₈,Ta₄)Si_0.75 bulk metallic glass composite (BMG-C) in dry air in the supercooled liquid state (SLS at 430 °C and 480 °C) and the crystallization state (CS at 520 °C and 560 °C) for 100 h were studied herein. Test results showed that the oxidation kinetics of the BMG-C in the SLS and CS followed a multi-stage oxidation rate law. The scales forming in both the SLS and CS consist of t-ZrO₂, and m-ZrO₂, CuO and Ag. In the CS, additional Al₂O₃ was observed. In the substrate area, Cu ₁₀Zr₇ crystalline likely formed in the amorphous substrate in the SLS. In the CS, more crystallization phases were found in the substrate, including additional CuZr₂ observed at temperatures ≤520 °C; AlCu₂Zr was observed at 560 °C. The Ta-reinforced phase in the BMG-C was more likely to react with Si in the scales forming Ta₂Si at temperatures ≤480 °C, which resulted in cracks in the Ta. Furthermore, channels between Ta precipitates and the matrix might exist, facilitating oxygen diffusivity. As the oxidation temperature (e.g., CS) and test duration were increased, the effects of the cracks and the channels became more significant and were responsible for the fast-growth oxidation in the final stage of the test.