Using hybrid molecular dynamics and Monte Carlo simulations, we examine the role of lattice distortion (LD) and chemical short-range ordering (CSRO) on the development of defects ahead of a mode I crack in medium entropy alloy CoCrNi. We show that CSRO noticeably increases fracture toughness. The result can be explained by the effect of CSRO on lowering LD and increasing intrinsic stacking fault energy and the direct impact CSRO has on the energetic barriers for emitting partial dislocations and forming nanotwins from CoCr clusters on the crack tip. CSRO allows the nanotwin domains to further support inelastic deformation, such as dislocation glide and amorphization, leading to stable crack-tip plasticity and postponement of softening. These findings imply that the superior fracture toughness in CoCrNi can be attributed to the non-negligible CSRO that naturally exists.

中文翻译：

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化学短程有序提高中熵合金CoCrNi的断裂韧性

利用混合分子动力学和蒙特卡罗模拟，我们研究了晶格畸变 (LD) 和化学短程有序 (CSRO) 对中熵合金 CoCrNi 中 I 型裂纹之前缺陷发展的作用。我们发现 CSRO 显着提高了断裂韧性。该结果可以通过 CSRO 对降低 LD 和增加本征堆垛层错能的作用以及 CSRO 对发射部分位错和在裂纹尖端由 CoCr 团簇形成纳米孪晶的能量势垒的直接影响来解释。 CSRO允许纳米孪晶域进一步支持非弹性变形，例如位错滑移和非晶化，从而导致稳定的裂纹尖端塑性和软化的推迟。这些发现意味着 CoCrNi 优异的断裂韧性可归因于自然存在的不可忽视的 CSRO。