由於高/中熵合金展現許多特殊性質，是近年重點研究的領域，常見為 γ' 與 σ 相作為強化相，對於 η析出相之探討則相對稀少。η 相為超合金領域中常見之第二相，其多變的形貌對於合金之微結構與機械性質有不同的影響。本研究將針對 η 相在高/中熵合金領域中析出行為進行更深入的探討。
本研究將以 Co-Cr-Ni 中熵合金系統為基地相，透過添加 Ti 促使 η 相析出。結合相模擬預測，分析並控制 Co 與 Ni 元素之比例，設計出僅由 η 與 γ 雙相之中熵合金。研究熱機處理製程，藉由冷滾軋以及不同溫度之時效處理製程，獲得最佳微結構，由奈米級圓球狀 η 析出相與 γ 基地相。在室溫下，其拉伸降伏強度與抗拉強度達 1724 MPa 與 1955 MPa，伸長量有 2.87%；在 600 ºC 高溫拉伸之降伏強度與抗拉強度依然保有 542 MPa 與 843 MPa，伸長量達 7.47%。
本研究以 X 光繞射與電子顯微鏡深入探討 η 相與 γ 相之晶體結構與取向關係，顯示兩相僅滿足 [011]γ // 〖"[2" "1" ̅"1" ̅"0]" 〗_"η" 關係，為非契合界面，透過高解析原子影像計算其晶格錯合為 -2.42%。

In recent years, high/medium-entropy alloys have been the focus of much research in recent years due to their special and unique properties. γ' and σ phases are commonly used as strengthening phase within the scope of subject of high/medium-entropy alloys, and discussion of the η phase is relatively rare. The η phase is one of the secondary phases in the field of superalloys, and its variable morphology has different effects on the microstructure and mechanical properties of alloys. In this study, we will focus on the precipitation behavior of η phase in the field of high/medium-entropy alloys.
Firstly, a Co-Cr-Ni medium-entropy alloy system will be used as the matrix, and Ti will be added to induce the precipitation of the η phase. A medium-entropy alloy composed of only two phases of η and γ is designed by controlling the amount of Co and Ni using CALPHAD. Research on the thermomechanical process, the alloy is then subjected to cold rolling and aging treatment processes at different temperatures, and the end results show that the alloys are consist of the γ matrix and the nano-scale spherical η phase, which is the optimal morphology. The alloys have a yield and tensile strength of 1724 MPa and 1955 MPa respectively at room temperature, and an elongation of 2.87%; high-temperature tensile testing at 600 ºC finds that yield and tensile strength remain at 542 MPa and 843 MPa respectively, and an elongation of 7.47%.
In additions, X-ray diffraction and electron microscopy were conducted to investigate the crystal structure and the orientation relationship of the η phase and the γ phase. The results show that the two phases only satisfy the relationship of [011]γ // 〖"[2" "1" ̅"1" ̅"0]" 〗_"η" , which is an incoherent interface. The lattice misfit is calculated -2.42% by the high-resolution lattice imaging.

致謝 II
摘要 V
Abstract VI
目錄 VIII
壹、 前言 1
貳、 文獻回顧 3
2-1 鎳基超合金 [9-11] 3
2-1.1 發展與應用 3
2-1.2 鎳基超合金強化機制與元素關係 5
2-1.3 析出強化機制 11
2-1.4 D024 — Ni3Ti η 析出相 16
2-1.5 L12 phase ─ Ni3(Al,Ti) γ' 析出相 20
2-1.6 γ' 析出相與 η 析出相之關係 22
2-1.7 FCC之破斷模式 24
2-2 高熵合金 [30] 25
2-2.1 高熵合金的定義與近期發展 26
2-2.2 高熵合金四大核心效應 27
2-2.3 CoCrNi 合金微結構與機械性質探討 34
2-2.4 高熵超合金之演變 36
2-2.5 Co1.5CrFeNi1.5Ti0.5 [40] 38
參、 研究方法 40
3-1 實驗流程簡介 40
3-2 合金製備 43
3-2.1 合金原料配製與真空電弧熔煉 43
3-3 高溫熱處理與冷滾軋製程 44
3-3.1 固溶處理 44
3-3.2 冷滾軋 44
3-3.3 快速退火 44
3-3.4 時效處理 44
3-4 微結構分析與晶體繞射分析 45
3-4.1 試片製備 45
3-4.2 掃描式電子顯微鏡 (Scanning Electron Microscopy, SEM) 45
3-4.3 X-ray繞射分析 (X-Ray Diffraction, XRD) 46
3-4.4 電子背向散射繞射 (Electron Backscattered Diffraction, EBSD) 46
3-4.5 穿透式電子顯微鏡 (Transmission Electron Microscopy, TEM) 47
3-5 機械性質分析 48
3-5.1 硬度量測 48
3-5.2 拉伸試驗與影像分析 48
3-6 相模擬分析 50
3-6.1 Thermo-calc 50
肆、 結果與討論 51
4-1 Co-Cr-Ni-Ti 中熵合金基地相與析出行為之研究 51
4-1.1 (CoCrNi)100-xTix 相模擬 52
4-1.2 T5 鑄造態之微結構 54
4-1.3 T5 固溶態處理與冷滾軋製程 56
4-1.4 T5 快速退火製程 59
4-1.5 T5 時效處理製程 61
4-1.6 T5 時效態之相分析與 σ 析出行為 67
4-2 非等莫耳 Co-Cr-Ni-Ti 中熵合金析出行為探討 71
4-2.1 NT5 鑄造態之微結構 73
4-2.2 NT5 固溶處理與冷滾軋製程 75
4-2.3 NT5 時效處理溫度對析出行為之影響 76
4-2.4 NT5 時效處理時間對析出行為之影響 85
4-3 奈米級球狀η 相對 Co-Cr-Ni-Ti 中熵合金之影響 91
4-3.1 奈米級球狀η 相與 γ 基地相之微結構 91
4-3.2 析出相高溫下之相穩定性 99
4-3.3 NT5 熱處理之機械性質 102
伍、 結論 112
陸、 本研究之貢獻 114
柒、 未來研究方向 115
捌、 參考文獻 116

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