「高熵合金」為多元素以相近比例混合並呈穩定固溶相之合金， 其組成原子大小差異所致之晶格扭曲效應，造就許多特殊的機械性 質。其中，BCC 結構的耐火高熵合金在室溫時擁有較高的硬度、在 高溫下也能維持一定的強度以及良好的相穩定性，為一個值得探討 的領域。因此本研究對 BCC 系列金屬及合金包括 W、WTa、 WTaMo、WTaMoNb 與 WTaMoNbV 進行基本特性分析與機械性質 量測。基本特性分析部分包含密度測量、XRD 量測及 EBSD 晶粒方 向鑑定，機械性質部分則藉由奈米壓痕測試、SEM 臨場微米柱壓 縮、TEM 臨場奈米柱壓縮觀察並分析不同元素數與晶體方向之單晶 合金的機械行為。實驗發現高熵合金具有包括晶格扭曲膨脹、彈塑 性異向性減弱、口香糖變形及大量部分差排短距離移動等，許多與 傳統合金結構及變形行為顯著差異之處，為探索高熵合金核心原理 的未來研究方向提供重要的訊息。

High-entropy alloys (HEAs) are entropy-stabilized solid solutions that consist of multi-principal elements. Severe lattice distortion comes from the different atom sizes that provide HEAs a lot of unprecedented mechanical properties. Among this novel family, BCC HEAs, particularly BCC HEAs based on refractory elements like WTaMoNbV, has high phase stability and large mechanical strength at elevated temperatures. This research was thus conducted on a series of BCC alloys consisting of W, WTa, WTaMo, WTaMoNb and HEA WTaMoNbV by measuring their basic properties and mechanical properties. Basic property analyses included density measurement, X-ray diffraction and electron backscatter diffraction (EBSD). Mechanical experiments included nanoindentation, in-situ SEM compression and in-situ TEM compression. Experimental results showed numerous unique characteristics in both deformation behavior and crystal structure between traditional alloys and HEAs, including lattice distortion/expansion, reduced elastic/plastic anisotropy, gum-like deformation and the short-distance movement of abundant partial dislocations that provide further insight for future study of HEA’s core effect and compositional theory.

摘要………………………………………………………..............I
Abstract……………………………………………………….........Ⅱ
目錄………………………………………………………..............Ⅲ
表目錄………………………………………………………..........Ⅶ
圖目錄………………………………………………………..........Ⅷ
壹、前言………………………………………………………......1
貳、文獻回顧…………………………………………………......2
2-1 高熵合金…………………………………………………....2
2-1-1 高熵合金之發展……………………………………….2
2-1-2 高熵合金核心效應…………………………………….4
2-1-3 高熵合金之特性與應用……………………………….6
2-2 高熵合金之機械行為……………………………………....9
2-2-1 部分差排、疊差及變形雙晶變形機制…………….....9
2-2-2 相變化變形機制…………………………………….....10
2-2-3 晶界遷移緩慢…………………………………….........11
2-3 材料機械行為及其影響因素…………………………........16
2-3-1 晶體結構…………………………………….................16
2-3-2 異向性…………………………………….............18
2-3-3 材料成分比例………………………………….............22
2-3-4 微結構………………………………………………….26
2-3-5 尺寸效應…………………………………….................29
2-4 結構扭曲及其分析……………………………………........31
2-4-1 結構扭曲…………………………………………….....31
2-4-2 結構扭曲之理論計算……………………………….....36
2-4-3 結構扭曲之模擬分析……………………………….....38
2-4-4 結構扭曲之實驗分析……………………………….....40
2-5奈米尺度機械行為分析…………………………………….44
2-5-1 奈米壓痕測試 (Nanoindentation)……………………..44
2-5-2 臨場掃描式電子顯微鏡 (In-situ SEM) 分析…………46
2-5-3 臨場穿透式電子顯微鏡 (In-situ TEM) 分析…………49
2-6 研究目的…………………………………………………....51
參、實驗步驟…………………………………………………......53
3-1 實驗規劃…………………………………………………....53
3-2 實驗步驟…………………………………………………....54
3-2-1 低熵、中熵、高熵合金試片製備……………………54
3-2-2 成分分析與理論計算………………………………….56
3-2-3 基本特性分析……………………………………….....59
3-2-4 機械性質測試……………………………………….....62
3-2-5 聚焦離子束 (FIB) 臨場試片製備……………………64
3-2-6 臨場 SEM 壓縮測試 (In-situ SEM Compression)…….67
3-2-7 臨場 TEM 壓縮測試 (In-situ TEM Compression)……70
肆、結果與討論…………………………………………………..72
4-1 基本特性分析……………………………………………....72
4-1-1 材料密度……………………………………………....72
4-2-2 X 光繞射分析……………………………………….....74
4-2-3 EBSD 晶粒方向鑑定……………………………….....77
4-2 奈米壓痕測試分析………………………………………....79
4-2-1 彈性模數 (Elastic Modulus)…………………………...79
4-2-2 硬度 (Hardness)………………………………………..80
4-3 臨場 SEM 壓縮測試分析…………………………………91
4-3-1 低熵至高熵合金壓縮後外觀之比較………………….91
4-3-2 低熵至高熵合金之應力應變曲線…………………....92
4-4 微米柱縱剖面變形微結構觀察……………………………102
4-5 臨場 TEM 壓縮測試分析…………………………….........109
4-5-1 純鎢金屬……………………………………………….109
4-5-2 高熵合金……………………………………………….109
4-5-3 低熵至高熵合金之比較……………………………….110
4-6 變形機制綜合比較分析…………………………………...113
伍、結論……………………………………………….................118
陸、參考文獻…………………………………………..................120

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