| Summary: | 碩士 === 義守大學 === 材料科學與工程學系 === 102 === The oxidation behavior of a novel Ni-free (Zr48Cu32Al8Ag8,Ta4)Si0.75 bulk metallic glass composite (BMGC) in dry air in the amorphous state(at 400oC), supercooled liquid state (SLS at 430oC and 480oC) and the crystallization state (CS at 520oC and 560oC) for 100 hours were studied herein.
Test results showed that the oxidation kinetics of the BMGC in the amorphous state, SLS and CS followed a multi-stage oxidation rate law. The scales forming in all the amorphous state, SLS and CS consist of t-ZrO2, and m-ZrO2, CuO and Ag. In the CS, additional Al2O3 was observed. In the substrate area, Cu10Zr7 crystalline likely formed in the amorphous substrate in the SLS. In the CS, more crystallization phases were found in the substrate, including additional Zr2Cu observed at temperatures ≥ 520oC; AlCu2Zr was observed at 560oC.
The Ta-reinforced phase in the BMGC was more likely to react with Si in the scales forming Ta2Si at temperatures ≥ 480oC, 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.
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