高熵合金為多種主元素以相近比例混合形成之合金，由於組成元素種類眾多，原子間尺寸差異導致嚴重晶格扭曲效應，造就了許多異於傳統的特殊機械性質與變形行為。尤其在不同溫度下，高熵合金仍能表現出擁有高強度、高延展性、破壞韌性、高溫穩定性、抗疲勞能力等絕佳的機械性質。其中，BCC 結構的耐火高熵合金在高溫下能夠維持相穩定性，同時具備極佳的抗軟化能力。因此延續本實驗室過去對BCC 低熵至高熵合金室溫機械性質與變形行為的研究，本研究在不同溫度下對BCC結構一元 (1B) W、三元 (3B) WTaMo與五元 (5B) WTaMoNbV 高熵合金不同晶粒方向進行奈米壓測試、微米柱壓縮測試及微米柱TEM 縱剖面分析，來探討溫度對高熵合金特殊機械性質影響及其背後的變形機制。實驗結果顯示，高熵合金彈性異向性及塑性異向性在任何溫度皆比傳統合金來得小。高熵合金微米柱壓縮滑移平面及應力應變曲線抖動皆較傳統合金不明顯，顯示高熵合金差排移動傾向短程差排滑移為主，同時高熵合金維持較高降伏強度的特性，表現出高熵合金優於傳統合金的高溫抗軟化能力。

High-entropy alloys (HEAs) are solid solutions that consist of multi-principal elements with near-equimolar ratios. Due to the diversity of constituent elements, atomic size difference leads to severe lattice distortion effect, which results in many special mechanical properties that are unique from traditional ones. At different temperatures, high-entropy alloys also exhibit excellent mechanical properties such as high strength, ductility, fracture toughness, high temperature stability and fatigue resistance. Among all this family, the refractory high-entropy alloy with BCC structure can maintain phase stability at high temperatures and has excellent softening resistance. Therefore, continuing our laboratory's previous research on the mechanical properties and deformation behavior of BCC low to high-entropy alloys at room temperature, in this research we conducted nanoindentation tests, micropillar compression test and TEM cross-section observation on grains with different crystallographic orientations from W, WTaMo and WTaMoNbV high-entropy alloys at different temperature to explore the effect of temperature on mechanical properties and deformation mechanism. Research shows that the elastic and plastic anisotropy of high-entropy alloys are smaller than traditional alloys at any temperature. Slip plane of high-entropy alloys and serrations of stress-strain curve are less obvious than traditional alloys, showing that high-entropy alloys tend to move in short-range dislocation slips. High-entropy alloys maintain the characteristics of high yield strength, which has better high-temperature softening resistance than traditional alloys.

目錄
誌謝 I
摘要 II
Abstract III
目錄 IV
圖目錄 VII
表目錄 XIV
壹、前言 1
貳、文獻回顧 2
2-1高熵合金 2
2-1-1高熵合金發展 2
2-1-2四大核心效應 5
2-1-3不同溫度下高熵合金之特殊性質表現 7
2-2高熵合金之機械行為 12
2-2-1部分差排與疊差 12
2-2-2變形雙晶 14
2-2-3相變誘發塑性 16
2-2-4高熵合金特殊差排/缺陷行為 18
2-3材料機械行為及其影響因素 25
2-3-1晶體結構 25
2-3-2組成元素 27
2-3-3尺寸效應 29
2-3-4異向性 31
2-4微奈米機械性質分析 35
2-4-1奈米壓痕測試 (Nanoindentation) 35
2-4-2微奈米柱壓縮測試 37
2-4-3臨場TEM拉伸測試 (In-situ TEM) 39
2-5研究目的 41
3-1實驗規劃 42
3-2實驗流程 43
3-2-1低、中、高熵合金試片 43
3-2-2 XPM機械性質量測 45
3-2-3聚焦離子束 (FIB) 微米柱試片製備 47
3-2-4不同溫度下之微米柱壓縮測試 49
3-2-5縱剖面TEM試片製備及觀察 51
肆、結果與討論 52
4-1晶粒方向鑑定 52
4-2不同溫度下之奈米壓痕測試分析 54
4-2-1楊氏模數 (Young’s Modulus) 54
4-2-2奈米硬度 (Nano Hardness) 61
4-3不同溫度下之微米柱壓縮測試 68
4-3-1低溫壓縮測試 68
4-3-2高溫壓縮測試 69
4-3-3應力應變曲線及鋸齒抖動行為 85
4-4縱剖面TEM試片觀察 90
伍、結論 94
陸、參考文獻 96
 

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