The intricate mechanism underlying brittle fractures in steel materials, particularly Zn-induced liquid metal embrittlement in BCC Fe, remains poorly understood. Accordingly, systematic investigations on crack propagation in BCC Fe, leveraging the anisotropic linear elastic fracture mechanics and a state-of-the-art Fe-Zn binary machine learning moment tensor potential, were performed in this work. Both theoretical analyses and atomic simulations reveal that the (001)[110] crack is intrinsically brittle, whereas the (110)[11¯0] crack can be blunted due to the emission of 〈111〉 dislocations, exhibiting a certain degree of toughness. At elevated temperatures, the reduced unstable stacking fault energy promotes dislocation emission. Zn doping facilitates the (001)[110] crack to propagate at lowered loads and enhances the dislocation emission of the (110)[11¯0] crack. Notably, our atomic simulations reveal a novel mechanism of Zn-induced liquid metal embrittlement: while Zn enhances dislocation emission at the crack tip, it fails to effectively blunt the crack. Instead, Zn infiltrates the crack surface via the steps caused by dislocation emission, ultimately driving brittle crack propagation.

中文翻译：

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BCC Fe 中的裂纹扩展和 Zn 的影响：原子探索


人们对钢材料脆性断裂的复杂机制，特别是 Zn 诱导的 BCC Fe 液态金属脆化仍然知之甚少。因此，本工作利用各向异性线性弹性断裂力学和最先进的 Fe-Zn 二进制机器学习矩张量势，对 BCC Fe 中的裂纹扩展进行了系统研究。理论分析和原子模拟均表明，（001）[110] 裂纹本质上是脆性的，而 （110）[11 ̄0] 裂纹由于〈111〉位错的发射而变钝，表现出一定的韧性。在高温下，不稳定堆积故障能量的降低促进了位错发射。Zn 掺杂有利于 （001）[110] 裂纹在较低载荷下扩展，并增强了 （110）[11 ̄0] 裂纹的位错发射。值得注意的是，我们的原子模拟揭示了 Zn 诱导液态金属脆化的一种新机制：虽然 Zn 增强了裂纹尖端的位错发射，但它无法有效地钝化裂纹。相反，Zn 通过位错发射引起的步骤渗入裂纹表面，最终驱动脆性裂纹扩展。