本研究根據晶格扭曲程度設計了五款面心立方(Face-Centered Cubic, FCC)合金，分別為Ni (1A)、Ni-2 at.% W (1A2)、Ni-4 at.% W (1A4)、CrFeNi (3A)、CoCrFeMnNi (5A)，並各自於不同狀態及溫度下進行機械性質的量測、變形行為的觀察，以及探討不同方向晶粒之塑性變形行為的差異，希望藉此釐清高熵合金所特有嚴重扭曲之晶格與其優異機械性能表現之間的關係。結果顯示，1A至5A隨著溶質原子的添加，晶格扭曲程度越趨嚴重，加上添加元素特性的影響，使得疊差能下降而讓分解的差排越難交叉滑移因此而提升加工硬化能力，進而減弱了晶體塑性變形異向性。拉伸性質方面，從1A、1A2到1A4，隨著W的添加，強度以及延展性都能有明顯的提升，展現出顯著的固溶強化效果。3A具有五種合金中最大的強度，但延展性最差。5A的強度比3A稍弱一點，但擁有較優異的延展性。透過應變硬化速率、應變硬化指數、Modified C-J analysis來進行分析，證實了1A至5A在越低溫環境具有越優異之應變硬化能力；且1A4、3A及5A在低溫下除了差排滑移以外，還能以變形雙晶的機制提供額外的加工強化並展現出更優異之機械性能。

FCC high-entropy alloy (HEA) CoCrFeMnNi exhibits outstanding tensile properties at room temperature and even better at cryogenic temperature. So far, by our limited knowledge, it could be roughly deduced that the deformation behavior of the CoCrFeMnNi HEA is related to its low stacking fault energy and the significant effect of solid solution strengthening. However, it’s still unclear that how the severely distorted lattice structure would alter the deformation behavior in the CoCrFeMnNi HEA. In this study, Ni (1A), Ni-2 at.%W (1A2), Ni-4 at.%W (1A4), CrFeNi (3A), and CoCrFeMnNi (5A) were designed based on the degree of lattice distortion. The results showed that the crystallographic plastic anisotropy of 5A is the weakest, which was also discussed with the relationship between lattice distortion and earing phenomenon. As for the tensile properties, from 1A, 1A2, and 1A4, with the addition of W, the strength and ductility could be significantly improved, showing a remarkable solid solution strengthening effect. 3A has the highest strength among the five alloys, but the ductility is the worst, while the strength of 5A is slightly weaker than that of 3A, but it has superior ductility. Strain hardening rate, strain hardening exponent, and modified C-J analysis were investigated in order to further understand the strain hardening behavior as the temperature decreases, and it’s confirmed that strain hardening ability of 1A to 5A all became better at lower temperature.

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