Cu45Zr45Al5Ag5非晶合金之空氣氧化行為研究

Air-oxidation of a Cu45Zr45Al5Ag5 Bulk Metallic Glass

本研究探討銅鋯基Cu45Zr45Al5Ag5 （以下簡稱CZ45）非晶合金在375℃~ 500℃空氣下的氧化行為。研究結果顯示，銅鋯基非晶合金的氧化動力學皆遵守兩段或三段式拋物線律（依溫度高低而異），而非晶的氧化反應速率常數（kp）與溫度呈現不規則之變化；即在過冷液態區間，kp值隨溫度上升而加快，但在450℃以上時，卻有相反的趨勢。氧化後的氧化生成物以正方晶體的ZrO2（t-ZrO2）和CuO為主，另外有少量的單斜及斜方的ZrO2（m-和o-ZrO2）以及α-Al2O3（只有在500℃生成）。此外，當溫度低於玻璃轉換溫度（Tg）下時，基材仍保有非晶狀態；但當溫度升高時，非晶合金會先氧化後結晶的相變化發生，使基材轉變為Cu10Zr7和ZrAl兩種結晶相。

The oxidation behavior of a Cu45Zr45Al5Ag5 bulk metallic glass (CZ45) was studied over the temperature range of 375 ~ 500 ℃ in dry air. The oxidation kinetics of the glassy alloy generally followed a two- to three-stage parabolic rate law, and the steady-state parabolic rate constants (kp values) fluctuated with temperature. The kp values increased with increasing temperature, when it was in the supercooled region; however, those values decreased with increasing temperature at T > 450 ℃. The scales formed on the CZ45-BMG 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 500 ℃). In addition, the glassy alloy underwent a pre-oxidation process, followed by a phase transformation after the oxidation at T > 400 ℃. The amorphous substrate remained unchanged at temperatures below the glass-transition temperature (Tg), while a dual-phase structure of Cu10Zr7 and ZrAl was developed after the oxidation at higher temperatures, indicating the crystallization of the amorphous substrate.