| Summary: | 碩士 === 國立臺灣海洋大學 === 材料工程研究所 === 97 === The oxidation behavior of three Cu-Zr based bulk metallic glasses, containing Cu45Zr45Al5Ag5 (CZ45-BMG), Cu43Zr43Al7Ag7 (CZ43-BMG), and (Cu43Zr43Al7Ag7)99.5Si0.5(CZ43S-BMG) was studied over the temperature range of 375 – 500oC in dry air. The oxidation kinetics of the three glassy alloys generally followed a multi-stage parabolic-rate law, and the steady-state parabolic-rate constants (kp values) fluctuated with temperature. It was found that kp values increased with increasing temperature, when it was below the supercooled region, however, those values decreased with increasing temperature at T > 450oC. The scales formed these BMGs consisted mostly of tetragonal-ZrO2 (t-ZrO2), CuO, minor amounts of monoclinic- and orthorhombic-ZrO2, (m- and o-ZrO2), and α-Al2O3 (only detected at 500oC). The formation of α-Al2O3 was responsible for the reduction of oxidation rates of these BMGs at 500oC. ZrO2 of different structures was depended strongly on temperature and duration of time.
In addition, small amounts of Ag and Si addition increased glass forming ability (GFA) and provided a better oxidation resistance at T < 425oC. However, no improvement was obtained at higher temperatures. In addition, three amorphous substrates retained unchanged at the temperature below the glass-transition temperature (Tg), however they underwent a pre-oxidation process and followed by the phase transformation after the oxidation at T > 400oC, having a dual-phase structure of Cu10Zr7 and ZrAl for both CZ45- and CZ43-BMG. On the other hand, CZ43S-BMG substrate transformed from the fully amorphous to the mostly Cu10Zr7 and minor Si2Zr crystallines. In summary, CZ45-BMG exhibited a better thermal stability among these BMGs studied.
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