滲鋁處理對高熵合金之高溫循環氧化行為影響

Investigation of High Temperature Cyclic Oxidation Properties of Pack Aluminized High Entropy Alloy at 1100 ℃

高熵合金自1995年開始發展至今，透過適當的合金配方設計可獲得高硬度、高加工硬化、耐高溫軟化、耐高溫氧化、耐腐蝕等特性。本研究針對成分為17.91% Fe -34.60% Cr -5.18% Al -24.64% Ni -17.66% Co （wt%）之高熵合金進行900℃，4小時之固體滲鋁處理。滲鋁試片與未處理之基材接著進行1100℃，每一次熱循環時間1小時，共196次的高溫循環氧化實驗，以測試滲鋁處理對於高熵合金高溫循環氧化性能的影響。經固體滲鋁處理之後的試片表面生成一層厚度約為26μm之β-NiAl相鋁化層，該鋁化層並固溶相當高含量之鐵、鉻、鈷等元素。由高溫循環氧化試驗之重量變化曲線、X光繞射圖形與截面定量分析結果可知，鋁化高熵合金的β-NiAl相鋁化層由於鋁原子向外與向內擴散而消失。不過鋁化處理高熵合金之抗高溫循環氧化特性仍優於未處理者。由於滲鋁處理之高熵合金在表層生成較明顯之氧化鋁保護層，因此在64次循環之前尚具有保護性。不過因為氧化鋁保護層於多次循環氧化之後剝落，因而降低鋁化高熵合金的抗高溫循環氧化性能。

Many efforts have been devoted to the study of High Entropy Alloy (HEA) due to their excellent properties and performance since 1995. It has been found that the HEA exhibits superior high temperature strength, unusual high temperature precipitation behavior and excellent high temperature oxidation resistance. In this work, a HEA with the following chemical compositions: 17.91% Fe -34.60% Cr -5.18% Al -24.64% Ni -17.66% Co (wt%) had been pack aluminized at 900 ℃ for 4 hrs. The β-NiAl layer around 26 μm in thickness was observed on surfaces of aluminized alloy. Protective and adhesive alumina scale was found on surfaces of the aluminide layers after cyclic oxidized at 1100oC for 64 times. A better high temperature oxidation resistance was observed with an aluminum packed HEA. It is also found that the β-NiAl layer disappeared due to the outward and inward diffusion of aluminum during high temperature cyclic oxidation. However, the spalling of alumina layer was revealed after 64 oxidation cycles, which reduces the performance of aluminized HEA against high temperature cyclic oxidation.