非等莫耳 Al-Co-Cr-Fe-Ni-Ti 高熵合金系統中，有相同於鎳基超合金之基地相與強化相結構。其中，又以本研究合金具最佳之相穩定性以及機械性質表現，經過 750℃ 進行 50 小時之時效處理，為單一 FCC 有序結構。熱處理時 discontinuous precipitation (DP) 相生成於晶界，影響高溫拉伸機械性質。本論文即透過不同的熱機處理製程，探討微結構及機械性質之演變，研究抑制 DP 相轉變之方法。
研究結果顯示，經滾軋製程 90% 後，在 1000℃ 以下退火溫度退火，可觀察到 DP 結構，使合金產生析出硬化效應，但會導致高溫延性的下降；在 1000℃ 以上之退火處理，再結晶之晶粒中無 DP 結構。然而，隨著晶粒成長，DP 又再析出於晶界區域。
因此，進一步研究不同退火時間，比較硬度、微結構觀察及 EBSD 分析。結果發現，當晶界析出物全數回溶，並於晶粒成長時再析出 DP 前，此時合金擁有最高之高角度晶界比率。故在此階段進行爐冷處理，可抑制 DP 之生成，並獲得優異之機械性質。室溫下之抗拉強度與伸長量，分別為 1320 MPa 與 31%，在 600℃ 高溫拉伸之強度與延性，分別為 1136 MPa 與33%。
此外，本研究以微量碳添加，在晶界上形成碳化物抑制 DP。實驗發現合金形成之碳化物為 TiC，其對於 DP 之抑制效果有限；當添加化合態 TiC 粉末於合金中雖能獲得較均勻之碳化物分佈及提供較高的室溫強化，但對於 1000℃ 高溫拉伸強度無明顯的改善。

None equal molar Al-Co-Cr-Fe-Ni-Ti high-entropy alloy system have been developed. Its microstructural morphologies and present of phases are similar to conventional Ni-based superalloys. After aged at 750℃ for 50h, the present alloy with single ordered FCC structure has optimized combination of phase stability and mechanical properties. But there is discontinuous precipitation (DP) phase observed in grain boundary during heat treatment, and it is detrimental to mechanical behavior at elevated temperature. The evolution of microstructure and mechanical properties with thermal-mechanical processing are studied and discussed, and the formation of DP phase can be eliminated further.
After 90% cold-rolled and annealing below 1000℃, the alloy shows significant precipitation hardening effect due to formation of DP, but it degrades the ductility at elevated temperarue; Above 1000℃, the alloy is recrystallized and no DP was obsearved in short time. However, the DP is still formed again in grain boundary due to the grain growth in long time.
By results of hardness, microstructure and EBSD, the highest fraction of high-angle grain boundary (HAGB) make the precipitates resolved into migrating grain boundaries, and DP start to reprecipitate during grain growth. However, the DP tends to form at HAGB, it can be successfully eliminated after annealing with furnace-cooling processing. The excellent mechanical properties can be obtained without DP phase, which are 1320 MPa/ 31% and 1136 MPa/ 33%, at 25℃ and 600℃, respectively.
Moreover, the addition of carbon in this alloy is also studied, and TiC carbides formed at grain boundary are limited to grow the DP effectively. Besides, the chemical-combined TiC powder are added, and the higher strengthening is obtatined with uniformly distribution of carbides at abiment temperature. The improvement of elevated strength is still finite in tensile test at 1000℃.

致謝
摘要 I
Abstract III
目錄 V
圖目錄 IX
表目錄 XV
第 1 章 前言 1
第 2 章 文獻回顧 3
2.1. 鎳基超合金 3
2.1.1. 鎳基超合金之發展及應用 [1, 2] 3
2.1.2. 鎳基超合金之強化機制 5
2.1.3. γ' (Ni3Al) 相 11
2.1.4. Discontinuous precipitation (DP) 14
2.1.5. 鎳基超合金中DP之抑制 16
2.1.6. 鎳基超合金中加碳之研究 17
2.2. 高熵合金 18
2.2.1. 緣起 18
2.2.2. 基本概念 18
2.2.3. 四大核心效應 22
2.2.4. 近期發展 27
2.2.5. 近期開發研究 29
2.3. FCC晶體系統 36
2.3.1. FCC晶體滑移系統 [8] 36
2.3.2. 部分差排與疊差能 [7] 37
2.3.3. 交叉滑移 39
2.3.4. 特殊晶界與退火雙晶 40
2.3.5. FCC之破斷模式 44
2.4. Grain growth law 45
2.5. Hall-Petch relation 46
2.6. 研究目的 48
第 3 章 實驗步驟 49
3.1. 合金組成 49
3.2. 實驗流程 51
3.3. 合金製備 52
3.3.1. 真空電弧熔煉 52
3.3.2. 高溫熱處理 53
3.3.3. 冷滾軋 54
3.4. 硬度量測 54
3.5. X-ray繞射分析 55
3.6. 微結構觀察 55
3.6.1. 光學式顯微鏡 (Optical Microscopy, OM) 55
3.6.2. 掃描式電子顯微鏡 (Scanning Electron Microscopy, SEM) 55
3.6.3. 電子微探儀 (Electron Probe Micro-Analyzer, EPMA) 55
3.7. 拉伸測試 56
3.7.1. 拉伸試片之製備 56
3.7.2. 低溫及常溫拉伸 56
3.7.3. 高溫拉伸 56
3.8. 熱差分析儀 (Differential Thermal Analysis, DTA) 56
3.9. 電子背向散射繞射 (Electron Backscattered Diffraction, EBSD) 57
第 4 章 結果與討論 58
4.1. Al0.2Co1.5CrFeNi1.5Ti0.3之微結構演變與機械性質 58
4.1.1. 固溶處理之時效態研究 58
4.1.2. 冷軋加工之退火態研究 67
4.2. 抑制 DP 相 87
4.2.1. 爐冷製程之研究 87
4.2.2. 爐冷態之微結構與機械性質 98
4.2.3. 爐冷態之時效處理 112
4.3. 添加碳對合金微結構與機械性質之影響 115
4.3.1. 合金添加元素態碳之分析 115
4.3.2. 合金添加元素態碳與元素態鈦之分析 125
4.3.3. 加碳滾軋態之機械性質及微結構綜合比較 130
4.3.4. 合金添加 TiC 粉末之分析 134
4.4. 晶粒成長 145
4.4.1. 晶粒成長與再結晶活化能 149
4.4.2. Hall-Petch relation 154
第 5 章 結論 156
第 6 章 本研究之貢獻 158
第 7 章 建議未來研究工作 159
第 8 章 參考文獻 160

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