臺灣博碩士論文加值系統

等莫耳比高熵合金CoCrFeMnNi在常溫常壓下為單一Face-centered cubic (FCC)相的合金，近期研究相信該高熵合金有低疊差能，低溫下因奈米雙晶有優秀的機械性質，但未觀察到相變現象。本研究利用角度解析式X-光繞射(Angular-dispersive X-ray diffraction ,ADXRD)高壓實驗，結果發現該高熵合金在7.1GPa時觀察到FCC至Hexagonal close packing (HCP)相的高壓相變，兩相持續共存到實驗最大壓力20GPa，卸載回常壓後仍有殘存HCP相，此過程為不可逆高壓相變。本研究也計算兩相的晶格常數、相比例與半高寬，也確認該高熵合金在高壓下非受到靜水壓力，受到非等向性的壓縮，材料在變形中將有對應的織構與滑移系統產生，與文獻比對發現高熵合金轉為HCP相後的織構分布與鋅在高壓下的結果相似，確認最終應轉變為單一HCP相，最後此研究也對高壓相變的機制進行探討。

An equal-molar CoCrFeMnNi high-entropy alloy has the cubic crystal system of face-centered-cubic (FCC) at room temperature and atmospheric pressure. The recent research believed that the high-entropy has the property of low stacking fault energy, and excellent mechanic property because of the structure of nanocrystalline in low temperature. However, there was no phase-changing observed. This research used Angular-dispersive X-ray Diffraction (ADXRD) under high-pressure, pressurized the CoCrFeMnNi high-entropy alloy system to 20GPa. After analyzing diffraction data, there was phase transformation from FCC to Hexagonal Close Packing (HCP) when the pressure reached 7.1GPa. Both phases existed until the maximum pressure of 20GPa. When the pressure was unloaded to atmospheric pressure, there are remaining HCP-phase in the alloy, which shows the phase transformation is a non-reversible phenomenon. Besides observing phase transformation under high-pressure and the remaining HCP phase, this research will also calculate the lattice constant, ratio and full width at half maximum (FWHM) of both phases. Then, the result of the analysis will be compared with other theses, and to ensure that high-entropy alloy will not be affected by hydrostatic pressure in a high-pressure environment and non-isotropic compression. During the transformation of the material, there was corresponding texture and slip system. After comparison with other thesis, we discovered that when the phase of that alloy was transformed to HCP, the texture distribution is similar with Zine under pressurized. And confirmed the final phase of the alloy should be a uniform single phase. Finally, this research will investigate the phase transformation mechanism under high-pressure environment.

一. 前言 1
二. 文獻回顧 3
2.1. 高熵合金的發展 3
2.1.1. 緣起 3
2.1.2. 高熵合金的定義 4
2.1.3. 高熵合金的主要效應 5
2.2. FCC 晶體變形系統 13
2.2.1. FCC 晶體滑移系統 13
2.2.2. 部分差排 14
2.2.3. Lomer-Cottrell Barrier 16
2.2.4. 疊差 17
2.3. 疊差能 18
2.3.1. 疊差能 18
2.3.2. 高熵合金CoCrFeMnNi的疊差能隨溫度變化 19
2.3.3. FCC結構高熵合金的負疊差能 22
2.4. 高壓實驗 26
2.4.1. 高壓相變 26
2.4.2. 純金屬Co、Cr、Fe、Mn、Ni的高壓相變 27
2.4.3. 合金CoCrNi、CoCrFeNi、CoCrFeNiPd的高壓相變 28
2.4.4. 合金Cr6Fe21MnNi9的高壓相變 32
2.4.5. 合金CoCrFeMnNi的高壓相變 34
三. 實驗步驟 36
3.1. 實驗設計 36
3.2. 實驗流程 37
3.3. 合金成分設計 37
3.4. 電弧熔煉 40
3.5. 光學式顯微鏡微結構觀察 42
3.6. 同步輻射繞射分析 43
3.7. 高壓實驗 44
3.8. 低溫XRD實驗 45
四.實驗結果 46
4.1. 金相微結構結果 46
4.2. 晶體結構分析 49
4.3. 低溫實驗結果 54
4.4. 高壓實驗 58
4.5. 應變等高線圖 64
4.6. 不同壓力下展開的繞射環 71
4.7. 晶格常數與單位晶格體積分析 82
4.8. 高壓實驗與文獻結果比較 88
五. 分析與討論 90
5.1. 半高寬分析 90
5.2. 高壓相變的穩定性 93
5.3. 高熵合金CoCrFeMnNi高壓FCC至HCP相相變機制 95
六. 結論 101
七. 未來工作 103
八.參考文獻 104
九.附錄 107
9.1. curriculum vitae (CV) 107
9.2. 熱膨脹係數量測 109
9.3. 彈性-黏塑性自我一致模型 Elastic Visco-Plastic Self Consistent model (EVPSC) 112
9.4. 第一原理模擬結果 119
9.5. 參賽海報 122
9.6. EVPSC教學 126

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