添加Er對Zr55Cu30Al10Ni5非晶合金氧化行為之影響

Effect of Er Addition on the Oxidation of Zr55Cu30Al10Ni5 Bulk Amorphous Alloys

本研究探討添加少量（2 at.%） Er對Zr55Cu30Al10Ni5塊狀非晶合金（以下簡稱Zr2Er-BMG）在溫度350 ~ 500℃之乾空氣下氧化行為。由實驗結果顯示，Zr2Er-BMG的氧化動力學遵守二至三階段的拋物線律，且非晶的氧化動力學常數（kp值）在結晶溫度（Tx = 473.2℃）之下時，會隨溫度上升而增加，但在溫度475 ~ 500℃時，kp值反而降低，此外，Zr2Er-BMG的氧化速率會比未添加Er非晶更快，顯示添加Er促進非晶的氧化反應。Zr2Er-BMG的氧化生成物因溫度不同而異，在350℃時大部分為tetragonal ZrO2 （t-ZrO2）及少部分monoclinic ZrO2 （m-ZrO2）、及CuO；而當溫度大於400℃，更有少量的Al2O3產生，而在Tg點以上時，m-ZrO2量會隨溫度上升而增加。當添加2%Er時，將有可能使Er+3離子取代少量Zr+4離子，進而增加氧離子的空孔濃度，使得氧離子內部擴散速率增加，致使Zr2Er-BMG的氧化速率比未添加Er的Zr55Cu30Al10Ni5非晶的氧化速率更快。此外，溫度在400℃及425℃時，基材結晶相為Zr2Cu；溫度大於450℃時，基材結晶相為CuZr2及Al2Zr3，顯示非晶氧化後，基材伴隨有結晶相變化發生。

The oxidation behavior of a (Zr55Cu30Al10Ni5)98Er2 bulk metallic glass (Zr2Er-BMG) was studied over the temperature range of 350 ~ 500 ℃ in dry air. The results showed that the oxidation kinetics of the Zr2Er-BMG followed a two-to-three-stage parabolic-rate law. The parabolic rate constant (kp values) generally increased with increasing temperature when it was below the crystalline temperature (Tx = 473.2 ℃), while the kp values fluctuated at temperatures above Tx. It was found that the addition of 2% Er enhanced the oxidation rate of the Zr2Er-BMG, as compared to that of the Er-free glassy alloy. The scales formed on the Zr2Er-BMG were strongly dependent on temperature, consisting exclusive tetragonal ZrO2 (t-ZrO2) at 350 ℃, while minor amounts of monoclinic ZrO2 (m-ZrO2), CuO, and Al2O3 were detected at T > 400 ℃. The amounts of m-ZrO2 increased with increasing temperature when it is above Tg In addition, the BMG substrate began to form crystalline Zr2Cu and Al2Zr3 beneath the scales after being oxidized at T > 400 ℃. It is most likely that the addition of 2% Er increased the concentration of oxygen vacancies in the defective ZrO2-lattice, which in turn enhanced inward diffusion of oxygen and led to the higher oxidation rate of the Zr2Er-BMG.