鎳基合金循環氧化行為數值模擬

Numerical Modeling on Cyclic Oxidation Behavior of Nickel-Base Alloys

當合金在熱循環作用下，於加熱過程中因氧化而增重，並在冷卻時，因氧化層與合金的熱膨脹差異會於氧化層形成壓應力而造成剝落。本研究分別以熱重分析方式及COSP（Cyclic Oxidation Spalling Program）模型數值方式分析探討，並模擬鎳基合金在高溫熱循環下之氧化行為。針對不同鉻及鈦含量之鎳基合金在高溫循環氧化過程中氧化層成長與剝落的情形，本研究先以熱重分析方式，獲得氧化層成長動力學常數及氧化層剝落之特性常數，再利用X光繞射、掃瞄式電子顯微鏡（SEM）配合能量分散光譜儀（EDS）進行元素成分分析以確定氧化層形態。由實驗獲得之動力學與氧化層組成結構，據以建立鎳基合金循環氧化數值模型之參數，再經由計算獲得各種不同鎳基合金循環氧化行為。計算之結果並與熱重分析之循環氧化實驗結果進行比較，其顯示此循環氧化動力學計算能與實驗結果相符。

Under cyclic oxidation, weight gain of an alloy due to oxygen uptake during heating and oxide spallation during cooling would occur because high compressive and thermal stresses in the oxide scale accumulate due to differences in thermal expansion coefficient between the alloy and the oxide. In the current study, the cyclic oxidation behavior of Ni-base alloys was investigated using a continuous thermogravimetric method and a computer simulation model COSP (Cyclic Oxidation Spalling Program). The thermogravimetric analysis was used to determine the oxidation kinetics and to obtain the oxide spalling parameters of various chromium and titanium containing Ni-base alloys for computer simulation. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX) were used to establish the compositions and structures of the oxide scales. With the parameters of oxidation spalling of Nibase alloys being applied into the modeling work, the cyclic oxidation behavior can be predicted. The simulation results showed a good agreement with experimental measurements.