以五元或五元以上近等莫耳元素組成之高熵合金設計概念已逐漸受國內外矚目。美國空軍實驗室首先將高熵合金概念結合耐火元素組成，於2010年開始發表一系列耐火高熵合金，第一組耐火高熵合金 NbTaMoW、VNbTaMoW，具有優異的高溫壓縮強度 (1600°C時為477 MPa)，但其缺點為室溫延性不佳且密度過高，因此不利於實際應用，隨後又發表第二組耐火高熵合金HfNbTaTiZr，其室溫壓縮塑性應變量大於50%，具有很好的延性，但其高溫強度仍不足夠，且抗氧化性不佳，因此本實驗室以HfNbTaTiZr 為基底開始進行一系列的合金設計改良。
由先前學長研究發現，HfNbTaTiZr添加Al、Si皆能有效提升高溫抗氧化能力，而添加Mo、Si能使高溫強度提升，綜合以上考量設計出本研究之耐火高熵合金Al-Mo-Nb-Ta-Ti-Zr，對Mo增量與微量添加Si跟Ni探討其對合金性質之影響。
由實驗結果得知，四種合金皆為BCC之結構，其中添加Si之合金有矽化物 (hexagonal結構) 峰值出現；高溫強度方面，Mo增量、Si添加皆使強度上升，但Ni添加不利於高溫強度；高溫抗氧化方面，Si添加對合金抗氧化力有明顯幫助，Mo與Ni則有負面的影響。
綜合來看，本研究表現最佳之AS合金兼顧了室溫延性、高溫強度及高溫抗氧化能力，且900 °C以上高溫強度更勝商用單晶鎳基超合金CMSX-4，具有高溫應用的潛力。

The concept of high-entropy alloy which combines equal or nearly equal quantities of elements has received lots of attention and research. Air Force Research Laboratory first reported refractory high-entropy alloy NbTaMoW and VNbTaMoW based on this concept in 2010. VNbTaMoW has high compressive yield strength of 1246 MPa at room temperature and excellent compressive yield strength of 477 MPa at 1600 °C, but has poor room-temperature ductility and much higher density. Afterwards, they reported new refractory high-entropy alloy HfNbTaTiZr with excellent ductility at room temperature and lower density. But, this alloy has poor oxidation resistance and low high-temperature strength. In order to overcome these drawbacks, our laboratory developed new compositions based on HfNbTaTiZr in recent years.
From the previous studies in our laboratory, we found the addition of Al and Si in HfNbTaTiZr effectively enhances high-temperature oxidation resistance and the addition of Mo and Si improves high-temperature strength. So, refractory high-entropy alloy Al-Mo-Nb-Ta-Ti-Zr is designed in this study. Besides, the increment of Mo and the addition of Ni, Si will also be studied to see their effects on microstructure, mechanical properties and oxidation resistance.
X-ray patterns show that all Al-Mo-Nb-Ta-Ti-Zr series are single BCC crystal structure with the exception that AS alloy appears silicide peaks (hexagonal structure). Furthermore, the addition of Si improves high-temperature strength and oxidation resistance. However, the increment of Mo shows negative impact on oxidation resistance and Ni shows negative impact on all high-temperature property.
On the whole, AS alloy has the best room-temperature ductility and high-temperature strength. In addition, the high-temperature strength of this alloy is better than that of single-crystal Ni-based superalloy CMSX-4 up to 1100 °C. Therefore, this alloy is very promising in high temperature applications.

壹、 前言 1
貳、 文獻回顧 3
2.1 鎳基超合金發展與應用 3
2.2 耐火合金 5
2.2.1 鈮合金[1] 7
2.3 高熵合金[28] 9
2.3.1 開發背景 9
2.3.2 高熵合金的特性 11
2.3.3 耐火高熵合金 13
參、 實驗步驟 52
3.1 合金製備及實驗流程 52
3.1.1 合金設計 52
3.1.2 實驗流程 55
3.1.3 真空電弧熔煉 55
3.2 密度量測 56
3.3 機械性質量測 56
3.3.1 硬度量測 56
3.3.2 常溫壓縮試驗 57
3.3.3 高溫壓縮試驗 57
3.4 氧化增重試驗 60
3.5 微結構觀察 61
3.5.1 掃描式電子顯微鏡 61
3.5.2 X-ray 繞射分析 61
肆、 結果與討論 63
4.1 晶體結構、微結構與基本性質 63
4.1.1 晶體結構分析 63
4.1.2 微結構分析 66
4.1.3 合金之基本性質 74
4.2 壓縮試驗 80
4.2.1 常溫壓縮 80
4.2.2 高溫壓縮 87
4.3 氧化增重試驗 117
4.3.1 700 °C 氧化增重 118
4.3.2 900 °C氧化增重 129
4.3.3 1100 °C氧化增重 139
4.3.4 抗氧化性比較與氧化層成長機制探討 149
伍、 結論 156
陸、 本研究貢獻與未來研究方向 161
柒、 參考文獻 163

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