這篇論文主要想要瞭解高熵合金在壓力下的變化機制，利用高強度的X光繞射，可以非常清楚的知道高熵合金的內部構造。在不斷加壓之下，觀察其結構之變化。一般來說，當壓力不斷增大，高熵合金內部受到擠壓及應力影響，並且導致結構相變。
結構相變的定義為因為溫度、壓力等物理環境因素的改變而引起的結構的變化。在實驗中嘗試以壓力誘導〖Al〗_0.5 CrFe〖Co〗_1.5 〖Ni〗_1.5, 〖Ti〗_0.5 CrFe〖Co〗_1.5 〖Ni〗_1.5和〖Al〗_0.2 CrFe〖Co〗_1.5 〖Ni〗_1.5 〖Ti〗_0.3相變。A部分從Laue diffraction顯示在常壓下的三種高熵合金都是FCC結構。XRD圖顯示出高熵合金在高壓下緩慢的壓縮形變，但是整體結構依然維持穩定，傳壓介質氖在5 GPa的時候結晶化並且也隨著壓力形變。三種高熵合金的體積模數都在136 GPa左右，遠大於氖的10 GPa，其硬度以及高壓下的表現都非常相似。
B部分優化了我們數據遮罩的技術，將傳壓介質氖的訊號移除。〖Al〗_0.5 CrFe〖Co〗_1.5 〖Ni〗_1.5, 〖Ti〗_0.5 CrFe〖Co〗_1.5 〖Ni〗_1.5和〖Al〗_0.2 CrFe〖Co〗_1.5 〖Ni〗_1.5 〖Ti〗_0.3 三個樣品分別在14 GPa, 11.9 GPa和13.1 GPa相變，在FCC(111)的低角度出現了HCP(100)的峰。顯示高熵合金受壓力引導相變，導致部分FCC結構轉變為HCP結構。

This paper mainly wants to understand the mechanism of high-entropy alloys under pressure. Using high-intensity X-ray diffraction can clearly know the structure of high-entropy alloys, and observe the changes of structure under high pressure. Generally speaking, when pressure is continuously increased, the HEAs will be affected by distortion and stress, leading to the phase transformation.
Phase transformation is defined as the change in structure caused by changes in physical environmental factors such as temperature and pressure. The experiment tried to induce 〖Al〗_0.5 CrFe〖Co〗_1.5 〖Ni〗_1.5, 〖Ti〗_0.5 CrFe〖Co〗_1.5 〖Ni〗_1.5 and 〖Al〗_0.2 CrFe〖Co〗_1.5 〖Ni〗_1.5 〖Ti〗_0.3 phase transformation by pressure. Part A shows that the three HEAs are all FCC structures at atmospheric pressure in Laue diffraction. XRD patterns show the HEAs slowly compressed and deformed under high pressure, but the structure remains stable. Pressure medium neon crystallized at around 5 GPa and also deformed with the increasing pressure. The bulk modulus of the three HEAs is around 136 GPa, which is much larger than the 10 GPa of neon. The hardness and behavior under high-pressure of the three HEAs are very similar.
Part B optimizes our data masking technology to remove the signal of the pressure-transmitting medium neon. 〖Al〗_0.5 CrFe〖Co〗_1.5 〖Ni〗_1.5, 〖Ti〗_0.5 CrFe〖Co〗_1.5 〖Ni〗_1.5 and 〖Al〗_0.2 CrFe〖Co〗_1.5 〖Ni〗_1.5 〖Ti〗_0.3 have phase transformation at 14 GPa, 11.9 GPa and 13.1 GPa, respectively. HCP (100) appears at the low angle of FCC (111). It is shown that the high-entropy alloys undergo the pressure-induced phase transformation, resulting in a partial transformation of the FCC structure into the HCP structure.

摘要---I
Abstract---II
致謝---III
Contents---IIV
List of Figures---VII
List of Tables---XI
Chapter 1 Introduction---1
1.1 HEAs---1
1.2 Four core effects---3
1.2.1 High entropy effect---4
1.2.2 Sluggish diffusion---5
1.2.3 Severe lattice distortion---5
1.2.4 Cocktail effects---8
1.3 Motivation---10
Chapter 2 Literature review---13
Chapter 3 Instrumentation---19
3.1 Synchrotron radiation---19
3.2 APS beamline---23
3.2.1 13ID-D beamline---23
3.2.2 Diamond-anvil cell---24
3.2.3 Data analysis---26
3.3 TPS 21A beamline---29
3.3.1 Nanodiffraction---29
3.3.2 Sample preparation---30
Chapter 4 Results and Discussion---33
4.1 〖Al〗_0.5 CrFe〖Co〗_1.5 〖Ni〗_1.5, 〖Ti〗_0.5 CrFe〖Co〗_1.5 〖Ni〗_1.5 and 〖Al〗_0.2 CrFe〖Co〗_1.5 〖Ni〗_1.5 〖Ti〗_0.3 at atmospheric pressure---33
4.1.1 Laue diffraction mapping---33
4.1.2 X-ray fluorescence---43
4.1.3 X-ray diffraction at atmospheric pressure---46
4.2 X-ray diffraction pattern vs. Pressure---48
4.2.1 〖Al〗_0.5 Cr Fe〖Co〗_1.5 〖Ni〗_1.5---48
4.2.2 〖Ti〗_0.5 Cr Fe〖Co〗_1.5 〖Ni〗_1.5---53
4.2.3 〖Al〗_0.2 CrFe〖Co〗_1.5 〖Ni〗_1.5 〖Ti〗_0.3---57
4.3 Deformation---61
4.3.1 D-spacing vs. pressure---61
4.3.2 Lattice constant---63
4.3.3 Bulk modulus---66
4.4 X-ray diffraction pattern with neon masked---70
4.4.1 Pressurize---70
4.4.2 Depressurize---78
4.4.3 Deformation---81
4.5 Lattice strain and crystallite size---84
Chapter 5 Conclusion---91
Chapter 6 Future Works---92
Chapter 7 Reference---93

[1] Yeh, J‐W., et al. "Nanostructured high‐entropy alloys with multiple principal elements: novel alloy design concepts and outcomes." Advanced engineering materials 6.5 (2004): 299-303.
[2] Zhang, Weiran, Peter K. Liaw, and Yong Zhang. "Science and technology in high-entropy alloys." Science China Materials 61.1 (2018): 2-22.
[3] Yeh, J‐W. "Recent progress in high entropy alloys." Ann. Chim. Sci. Mat 31.6 (2006): 633-648.
[4] Yong Zhang. "History of high-entropy materials." High-Entropy Materials. Springer, Singapore (2019): 1-33.
[5] Yong Zhang. , et al. "Microstructures and properties of high-entropy alloys." Progress in materials science 61 (2014): 1-93.
[6] He, Quanfeng, and Yong Yang. "On lattice distortion in high entropy alloys." Frontiers in Materials 5 (2018): 42.
[7] Yeh, J‐W., et al. "Anomalous decrease in X-ray diffraction intensities of Cu–Ni–Al–Co–Cr–Fe–Si alloy systems with multi-principal elements." Materials chemistry and physics 103.1 (2007): 41-46.
[8] Ranganathan, S. "Alloyed pleasures: Multimetallic cocktails." Current science 85.10 (2003): 1404-1406.
[9] Cheng, Benyuan, et al. "Pressure-induced phase transition in the AlCoCrFeNi high-entropy alloy." Scripta Materialia 161 (2019): 88-92.
[10] Wang, Chenxu, et al. "Phase transformations of Al-bearing high-entropy alloys AlxCoCrFeNi (x= 0, 0.1, 0.3, 0.75, 1.5) at high pressure." Applied Physics Letters 114.9 (2019): 091902.
[11] Lin, Qingyun, et al. "Cryogenic-deformation-induced phase transformation in an FeCoCrNi high-entropy alloy." Materials Research Letters 6.4 (2018): 236-243.
[12] Wikipedia contributors. "Linear particle accelerator." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 16 May. 2021. Web. 15 Sep. 2021.
[13] Britannica, The Editors of Encyclopaedia. "Cyclotron". Encyclopedia Britannica, 8 Feb. 2018, https://www.britannica.com/technology/cyclotron. Accessed 15 September 2021.
[14] Eberhardt, W. "Synchrotron radiation: A continuing revolution in X-ray science—Diffraction limited storage rings and beyond." Journal of Electron Spectroscopy and Related Phenomena 200 (2015): 31-39.
[15] Wikipedia contributors. "Diamond anvil cell." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 4 Sep. 2021. Web. 15 Sep. 2021.
[16] Cornelius, Thomas W., and Olivier Thomas. "Progress of in situ synchrotron X-ray diffraction studies on the mechanical behavior of materials at small scales." Progress in Materials Science 94 (2018): 384-434.
[17] Li, Rui, et al. "Effect of defects on the phase transition of Al0. 1CoCrFeNi high-entropy alloy under high pressure." Intermetallics 140 (2022): 107388.
[18] Sistla, Harihar Rakshit, Joseph W. Newkirk, and F. Frank Liou. "Effect of Al/Ni ratio, heat treatment on phase transformations and microstructure of AlxFeCoCrNi2− x (x= 0.3, 1) high entropy alloys." Materials & Design 81 (2015): 113-121.
[19] Singh, A. K., et al. "Strength of iron under pressure up to 55 GPa from X-ray diffraction line-width analysis." Journal of Physics and Chemistry of Solids 67.9-10 (2006): 2197-2202.