The pursuit of enhancing strength and toughness remains a critical endeavor in the field of structural materials. This study explores two distinct strategies to overcome the traditional strength-toughness trade-off. Specifically, we manipulate the chemical composition and short-range order (SRO) of the NiCoCr medium-entropy alloy, which has shown remarkable fracture toughness in recent experiments. Utilizing molecular dynamics simulations, we uncover nano-scale deformation mechanisms during crack propagation. Our findings highlight that optimizing the SRO degree leads to improvements in both atomic scale strength and toughness defined as the area underneath stress-strain curves from MD simulations. In contrast, a trade-off between strength and toughness persists when only manipulating the Ni content in the NiCoCr alloy. Based on the simulation results, we establish a strong correlation between toughness, strength, surface energies, and unstable stacking fault energies. These factors are influenced by the chemical composition and SROs in NiCoCr, with SROs acting as strong obstacles to dislocations, thereby contributing to additional strength. The exceptional toughness of NiCoCr with SRO arises from a synergy of intrinsic and extrinsic mechanisms, including dislocation glide, nanobridging during nanovoid coalescence and zigzag crack path. It is found that, in the presence of SRO, intrinsic toughening mechanisms usually associated with crack tip blunting and dissipation can also facilitate the onset of extrinsic toughening mechanisms of nanobridging and zig-zag crack path associated with nanovoid formation and coalescence. This study emphasizes the importance of tailoring SRO in designing materials with enhanced strength and toughness.

中文翻译：

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调整化学短程顺序以同时增强 NiCoCr 中熵合金的强度和韧性

追求增强强度和韧性仍然是结构材料领域的一个关键努力。本研究探索了两种不同的策略来克服传统的强度-韧性权衡。具体来说，我们操纵了 NiCoCr 中熵合金的化学成分和短程有序 (SRO)，该合金在最近的实验中表现出了出色的断裂韧性。利用分子动力学模拟，我们揭示了裂纹扩展过程中的纳米级变形机制。我们的研究结果强调，优化 SRO 程度可以提高原子级强度和韧性，原子级强度和韧性定义为 MD 模拟中应力-应变曲线下方的区域。相比之下，当仅控制 NiCoCr 合金中的 Ni 含量时，强度和韧性之间的权衡仍然存在。根据模拟结果，我们建立了韧性、强度、表面能和不稳定堆垛层错能之间的强相关性。这些因素受到 NiCoCr 中化学成分和 SRO 的影响，其中 SRO 充当位错的强大障碍，从而有助于提高强度。具有 SRO 的 NiCoCr 的卓越韧性源于内在和外在机制的协同作用，包括位错滑移、纳米空隙聚结过程中的纳米桥接和锯齿形裂纹路径。研究发现，在 SRO 存在的情况下，通常与裂纹尖端钝化和消散相关的内在增韧机制也可以促进与纳米空隙形成和聚结相关的纳米桥接和锯齿形裂纹路径的外在增韧机制的发生。这项研究强调了定制 SRO 在设计具有增强强度和韧性的材料中的重要性。