等莫耳CoCrFeMnNi高熵合金為含有五個以上等莫耳原子比的主元素的固溶合金，其可展現出傳統單主元素合金具有更好的機械性能。本研究將以純鎳為底基，藉由添加不同數量的等莫耳主元素以形成不同熵值的合金，並就巨觀變形行為和內部微觀缺陷演化關係進行探討。本實驗使用的是國家同步輻射中心(National Synchrotron Radiation Research Center, NSRRC)的台灣光源(Taiwan Light Source, TLS) BL01B1(Nano-transmission X-ray Microscope)、BL17B2 (X-ray Scattering)、以及台灣光子源(Taiwan Photon Source, TPS) 的TPS-21A (X-ray Nanodiffraction)光束線，透過各式臨場高分辨率的X-光技術，以探討樣品在拉伸過程中合金內部微結構的演化與其變形行為間的關聯性，藉此了解多晶材料的織構特徵形成與缺陷演化。透過臨場所獲得的X-光繞射圖譜，能夠定量的估計差排密度、疊差機率、疊差能、以及雙晶機率等微結構特性參數，我們發現高熵合金與傳統合金在變形行為具有顯著的差異。由於高熵合金的嚴重晶格扭曲致使晶格能量提高，因此相較於中低熵合金有較低的疊差能。疊差能的下降，除了使得疊差在加工過程中更容易產生之外，也意味著更容易產生雙晶結構。值得一提的是，我們在實驗中發現疊差能會隨著應變量的增加而下降，此結果顛覆疊差能為定值的傳統觀念。除此之外，高熵合金織構的形成會隨著熵值越高而弱化，顯示高熵合金較一般傳統合金有較低的塑性異向性。另外本研究也使用J-PARC中心TAKUMI實驗站進行室溫臨場中子拉伸實驗，分析了不同熵值鎳基合金的彈性模數。實驗結果也證實除塑性異向性之外，高熵合金相對於中低熵合金有較低的彈性異相性。

Equiatomic CoCrFeMnNi high-entropy alloys (HEAs) are solid solution alloys, which contain more than five principal elements with nearly equal atomic percentage, reveals extra-ordinary mechanical properties relative to traditional single principal element alloys. In this work, we compared deformation behavior and internal defect evolutions among nickel-based low-to-high entropy alloys, including the CoCrFeMnNi high-entropy alloy. The experiment performed at BL01B1 and BL17B2 beamlines of Taiwan Light Source and TPS 21A Nanodiffraction beamline of Taiwan Photon Source. In-situ high-resolution synchrotron X-ray diffraction and microscopy techniques are used to reveal texture formation and defect evolution of the alloys during tensile deformation. Quantitative evolutions of dislocation density, stacking faults probability, twinning faults probability as well as corresponding stacking fault energy can be calculated using the X-ray diffraction analysis methods. We found that high-entropy alloys are very different from the traditional low entropy alloys in the deformation behavior. The stacking fault energy of high-entropy alloy is significantly lower than that of medium and low entropy alloys due to its severe lattice distortion. Therefore, stacking faults and twins can be produced easily in high-entropy alloys. We also found that the stacking fault energy decreases with the increase of strain, which is different from the traditional concept of fixed stacking fault energy during deformation. In addition, the texture formation is obvious as the increase of alloy entropy, which implies that high-entropy alloys exhibit lower plastic anisotropy than traditional alloys. Besides, elastic moduli of nickel-based alloys with different entropies were analyzed by using in-situ room temperature tensile neutron experiments carried out at TAKUMI beamline of Japan Proton Accelerator Research Complex facility. The experimental results also suggest that elastic anisotropy of high-entropy alloys is less obvious than medium- and low-entropy alloys.

1. Yeh, J. W.; Chen, S. K.; Lin, S. J.; Gan, J. Y.; Chin, T. S.; Shun, T. T.; Tsau, C. H.; Chang, S. Y., Nanostructured high‐entropy alloys with multiple principal elements: novel alloy design concepts and outcomes. Advanced Engineering Materials 2004, 6, 299-303.
2. Sun, S.; Tian, Y.; Lin, H.; Dong, X.; Wang, Y.; Zhang, Z.; Zhang, Z., Enhanced strength and ductility of bulk CoCrFeMnNi high entropy alloy having fully recrystallized ultrafine-grained structure. Materials & Design 2017, 133, 122-127.
3. Yeh, J.-W., Recent progress in high-entropy alloys. Annales de Chimie. Science des Materiaux (Paris) 2006, 31, 633-648.
4. Murty, B. S.; Yeh, J.-W.; Ranganathan, S.; Bhattacharjee, P., High-entropy alloys. Elsevier: 2019.
5. Ranganathan, S., Alloyed pleasures: multimetallic cocktails. Current science 2003, 85, 1404-1406.
6. Rao, J.; Diao, H.; Ocelík, V.; Vainchtein, D.; Zhang, C.; Kuo, C.; Tang, Z.; Guo, W.; Poplawsky, J.; Zhou, Y., Secondary phases in AlxCoCrFeNi high-entropy alloys: An in-situ TEM heating study and thermodynamic appraisal. Acta Materialia 2017, 131, 206-220.
7. Lim, X., Mixed-up metals make for stronger, tougher, stretchier alloys. Nature News 2016, 533, 306.
8. Sun, S.; Tian, Y.; An, X.; Lin, H.; Wang, J.; Zhang, Z., Ultrahigh cryogenic strength and exceptional ductility in ultrafine-grained CoCrFeMnNi high-entropy alloy with fully recrystallized structure. Materials Today Nano 2018, 4, 46-53.
9. Otto, F.; Dlouhý, A.; Somsen, C.; Bei, H.; Eggeler, G.; George, E. P., The influences of temperature and microstructure on the tensile properties of a CoCrFeMnNi high-entropy alloy. Acta Materialia 2013, 61, 5743-5755.
10. Joo, S.-H.; Kato, H.; Jang, M.; Moon, J.; Tsai, C.; Yeh, J.; Kim, H., Tensile deformation behavior and deformation twinning of an equimolar CoCrFeMnNi high-entropy alloy. Materials Science and Engineering: A 2017, 689, 122-133.
11. Yoshida, S.; Bhattacharjee, T.; Bai, Y.; Tsuji, N., Friction stress and Hall-Petch relationship in CoCrNi equi-atomic medium entropy alloy processed by severe plastic deformation and subsequent annealing. Scripta Materialia 2017, 134, 33-36.
12. Gao, M. C.; Yeh, J.-W.; Liaw, P. K.; Zhang, Y., High-entropy alloys: fundamentals and applications. Springer: 2016.
13. Wu, Y.; Liu, W.; Wang, X.; Ma, D.; Stoica, A. D.; Nieh, T.; He, Z.; Lu, Z., In-situ neutron diffraction study of deformation behavior of a multi-component high-entropy alloy. Applied Physics Letters 2014, 104, 051910.
14. Smith, W. F.; Hashemi, J.; Presuel-Moreno, F., Foundations of materials science and engineering. Mcgraw-Hill Publishing: 2006.
15. Laplanche, G.; Kostka, A.; Horst, O.; Eggeler, G.; George, E., Microstructure evolution and critical stress for twinning in the CrMnFeCoNi high-entropy alloy. Acta Materialia 2016, 118, 152-163.
16. Reed, R., The physical metallurgy of nickel and its alloys. Superalloys-Fundamentals and Applications 2006, 33-120.
17. Groves, G.; Kelly, A., Independent slip systems in crystals. Philosophical Magazine 1963, 8, 877-887.
18. Smallman, R.; Green, D., The dependence of rolling texture on stacking fault energy. Acta Metallurgica 1964, 12, 145-154.
19. Zaddach, A.; Niu, C.; Koch, C.; Irving, D., Mechanical properties and stacking fault energies of NiFeCrCoMn high-entropy alloy. Jom 2013, 65, 1780-1789.
20. Liu, J.; Chen, C.; Xu, Y.; Wu, S.; Wang, G.; Wang, H.; Fang, Y.; Meng, L., Deformation twinning behaviors of the low stacking fault energy high-entropy alloy: an in-situ TEM study. Scripta Materialia 2017, 137, 9-12.
21. Howie, A.; Swann, P., Direct measurements of stacking-fault energies from observations of dislocation nodes. Philosophical Magazine 1961, 6, 1215-1226.
22. Loretto, M.; Phillips, P.; Mills, M., Stacking fault tetrahedra in metals. Scripta Materialia 2015, 94, 1-4.
23. Otte, H. M., Measurement of Stacking‐Fault Energies by X‐Ray Diffraction. Journal of Applied Physics 1967, 38, 217-222.
24. Mote, V.; Purushotham, Y.; Dole, B., Williamson-Hall analysis in estimation of lattice strain in nanometer-sized ZnO particles. Journal of Theoretical and Applied Physics 2012, 6, 6.
25. Brown, L., The self-stress of dislocations and the shape of extended nodes. Philosophical Magazine 1964, 10, 441-466.
26. Silcox, J.; Hirsch, P., Dislocation loops in neutron-irradiated copper. Philosophical Magazine 1959, 4, 1356-1374.
27. Sousa, T. G.; Diniz, S. B.; Pinto, A. L.; Brandao, L. P., Dislocation Density by X-ray Diffraction in α Brass Deformed by Rolling and ECAE. Materials Research 2015, 18, 246-249.
28. Jenkins, R.; Snyder, R. L., Introduction to X-ray powder diffractometry. 1996.
29. Ribárik, G., Modeling of diffraction patterns based on microstructural properties. Material Science and Solid State Physics Program. Eötvös Loránd University Institute of Physics Department of Materials Physics 2008.
30. Groma, I.; Ungár, T.; Wilkens, M., Asymmetric X-ray line broadening of plastically deformed crystals. I. Theory. Journal of applied crystallography 1988, 21, 47-54.
31. Ribárik, G.; Ungár, T.; Gubicza, J., MWP-fit: a program for multiple whole-profile fitting of diffraction peak profiles by ab initio theoretical functions. Journal of Applied Crystallography 2001, 34, 669-676.
32. Dey, S.; Chatterjee, P.; Sen Gupta, S., Deformation stacking fault probability and dislocation microstructure of cold worked Cu–Sn–5Zn alloys by x-ray diffraction line profile analysis. Journal of applied physics 2006, 100, 073509.
33. Nyce, D. S., Linear position sensors. Wiley, New York 2004, 4, 62-77.
34. Patriksson, M., The traffic assignment problem: models and methods. Courier Dover Publications: 2015.
35. Varvenne, C.; Luque, A.; Curtin, W. A., Theory of strengthening in fcc high entropy alloys. Acta Materialia 2016, 118, 164-176.
36. Callister, W. D.; Rethwisch, D. G., Materials science and engineering: an introduction. John wiley & sons New York: 2007; Vol. 7.
37. Kocks, U.; Mecking, H., Physics and phenomenology of strain hardening: the FCC case. Progress in materials science 2003, 48, 171-273.
38. Jang, M. J.; Ahn, D.-H.; Moon, J.; Bae, J. W.; Yim, D.; Yeh, J.-W.; Estrin, Y.; Kim, H. S., Constitutive modeling of deformation behavior of high-entropy alloys with face-centered cubic crystal structure. Materials Research Letters 2017, 5, 350-356.
39. Guodong, W. S. L. Z. W., Influence of grain size on TWIP effect in a TWIP steel. Acta Metall Sin 2009, 45, 1083-1090.
40. Ren, S.; Wen, C.; Wu, X.; Gong, Y.; Long, Y.; Cheng, L.; Zhu, X., Influence of stacking fault energy and strain rate on the mechanical properties in Cu and Cu–Al–Zn alloys. Materials Science and Engineering: A 2013, 585, 174-177.
41. Zhang, P.; An, X.; Zhang, Z.; Wu, S.; Li, S.; Zhang, Z.; Figueiredo, R.; Gao, N.; Langdon, T., Optimizing strength and ductility of Cu–Zn alloys through severe plastic deformation. Scripta Materialia 2012, 67, 871-874.
42. Datta, A.; Waghmare, U.; Ramamurty, U., Structure and stacking faults in layered Mg–Zn–Y alloys: A first-principles study. Acta Materialia 2008, 56, 2531-2539.
43. Zhang, J.; Dou, Y.; Liu, G.; Guo, Z., First-principles study of stacking fault energies in Mg-based binary alloys. Computational Materials Science 2013, 79, 564-569.
44. Fan, Z.; Mingzhi, H.; Deke, S., The relationship between the strain-hardening exponent n and the microstructure of metals. Materials Science and Engineering: A 1989, 122, 211-213.
45. Lonsdale, D. K., International tables for X-ray crystallography. Kynoch Press: 1968.
46. Warren, B., X-ray studies of deformed metals. Progr. in Metal Phys. 1959, 8.
47. Peterson, N., MEASUREMENT OF PLANAR FAULT PROBABILITIES IN AUSTEMPERED DUCTILE IRON AND 304L STAINLESS STEEL. 2018.
48. Cohen, J. t.; Wagner, C., Determination of twin fault probabilities from the diffraction patterns of fcc metals and alloys. Journal of Applied Physics 1962, 33, 2073-2077.
49. Hull, D.; Bacon, D. J., Introduction to dislocations. Butterworth-Heinemann: 2001.
50. Reed, R. C., The superalloys: fundamentals and applications. Cambridge university press: 2008.
51. Zhang, J.-S., High temperature deformation and fracture of materials. Elsevier: 2010.
52. Suzuki, H., Segregation of solute atoms to stacking faults. Journal of the Physical Society of Japan 1962, 17, 322-325.
53. Lee, Y.-K.; Lee, S.-J.; Han, J., Critical assessment 19: stacking fault energies of austenitic steels. Taylor & Francis: 2016.
54. Park, M. C.; Kim, K. N.; Yun, J. Y.; Shin, G. S.; Kim, S. J., Strain-induced ε/α′ martensitic transformation behavior and solid particle erosion resistance of austenitic Fe–Cr–C–Mn/Ni alloys. Tribology Letters 2014, 54, 51-58.
55. Saeed-Akbari, A.; Imlau, J.; Prahl, U.; Bleck, W., Derivation and variation in composition-dependent stacking fault energy maps based on subregular solution model in high-manganese steels. Metallurgical and Materials Transactions A 2009, 40, 3076-3090.
56. Yen, C.-C.; Huang, G.-R.; Tan, Y.-C.; Yeh, H.-W.; Luo, D.-J.; Hsieh, K.-T.; Huang, E.-W.; Yeh, J.-W.; Lin, S.-J.; Wang, C.-C., Lattice distortion effect on elastic anisotropy of high entropy alloys. Journal of Alloys and Compounds 2019, 152876.
57. Reed, R.; Schramm, R., Relationship between stacking‐fault energy and x‐ray measurements of stacking‐fault probability and microstrain. Journal of Applied Physics 1974, 45, 4705-4711.
58. Latanision, R.; Ruff, A., The temperature dependence of stacking fault energy in Fe-Cr-Ni alloys. Metallurgical Transactions 1971, 2, 505-509.
59. Liu, S.; Wu, Y.; Wang, H.; Lin, W.; Shang, Y.; Liu, J.; An, K.; Liu, X.; Wang, H.; Lu, Z., Transformation-reinforced high-entropy alloys with superior mechanical properties via tailoring stacking fault energy. Journal of Alloys and Compounds 2019, 792, 444-455.