CrCoNi-based medium- and high-entropy alloys display outstanding damage tolerance, especially at cryogenic temperatures. In this study, we examined the fracture toughness values of the equiatomic CrCoNi and CrMnFeCoNi alloys at 20 kelvin (K). We found exceptionally high crack-initiation fracture toughnesses of 262 and 459 megapascal-meters ½ (MPa·m ½ ) for CrMnFeCoNi and CrCoNi, respectively; CrCoNi displayed a crack-growth toughness exceeding 540 MPa·m ½ after 2.25 millimeters of stable cracking. Crack-tip deformation structures at 20 K are quite distinct from those at higher temperatures. They involve nucleation and restricted growth of stacking faults, fine nanotwins, and transformed epsilon martensite, with coherent interfaces that can promote both arrest and transmission of dislocations to generate strength and ductility. We believe that these alloys develop fracture resistance through a progressive synergy of deformation mechanisms, dislocation glide, stacking-fault formation, nanotwinning, and phase transformation, which act in concert to prolong strain hardening that simultaneously elevates strength and ductility, leading to exceptional toughness.

中文翻译：

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CrCoNi 基中熵合金和高熵合金在 20 开尔文时具有出色的断裂韧性

基于 CrCoNi 的中熵和高熵合金显示出出色的损伤容限，尤其是在低温下。在这项研究中，我们检查了 20 开尔文 (K) 下等原子数 CrCoNi 和 CrMnFeCoNi 合金的断裂韧性值。我们发现了 262 和 459 兆帕米的异常高的裂纹起始断裂韧性½(兆帕·米½) 分别用于 CrMnFeCoNi 和 CrCoNi；CrCoNi 显示出超过 540 MPa·m 的裂纹扩展韧性½经过 2.25 毫米的稳定开裂。20 K 时的裂纹尖端变形结构与高温下的裂纹尖端变形结构截然不同。它们涉及堆垛层错、精细纳米孪晶和转变的 epsilon 马氏体的成核和受限生长，具有可以促进位错停滞和传输以产生强度和延展性的相干界面。我们认为，这些合金通过变形机制、位错滑移、堆垛层错形成、纳米孪晶和相变的渐进协同作用而产生抗断裂性，这些协同作用可延长应变硬化，同时提高强度和延展性，从而获得卓越的韧性。