The liquid metal embrittlement (LME) of advanced high-strength steels caused by zinc (Zn) has become a critical issue hindering their widespread application in the automotive industry. In this study, atomic-scale simulations are carried out to elucidate the underlying cause of this phenomenon, namely grain boundary embrittlement due to Zn segregation at iron (Fe) grain boundaries. A machine learning moment tensor interatomic potential for the Fe-Zn binary system is developed, based on which the thermodynamics of grain boundary segregation is evaluated. The yielded segregation energy spectrum of Zn in BCC Fe reveals the quantitative relationship between the average segregation concentration of Zn at Fe grain boundaries and the macroscopic Zn content, temperature, and fraction of grain boundary atoms. It suggests a strong thermodynamic driving force for Zn segregation at the Fe grain boundaries, which correlates directly with the grain boundary energy: high-energy grain boundaries can accommodate a large amount of Zn atoms, while low-energy grain boundaries exhibit a certain degree of repulsion to Zn. Kinetically, Zn enters the grain boundaries more easily through diffusion than by penetration. Nonetheless, the grain boundary embrittlement caused by Zn penetration is more severe than that by Zn diffusion. The embrittlement effect generally increases linearly with the increase in Zn concentration at the grain boundary. Altogether, it suggests that the LME in steels induced by grain boundary segregation of Zn emerges as a combined consequence of Zn melt penetration and solid-state diffusion of Zn atoms.

中文翻译：

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原子模拟揭示了 BCC Fe 晶界中的 Zn 偏析及其在液态金属脆化中的作用


锌 （Zn） 引起的先进高强度钢的液态金属脆化 （LME） 已成为阻碍其在汽车行业广泛应用的关键问题。在这项研究中，进行了原子尺度模拟以阐明这种现象的根本原因，即由于铁 （Fe） 晶界的 Zn 偏偏而导致的晶界脆化。开发了一种用于 Fe-Zn 二元系统的机器学习矩张量原子间势，并在此基础上评估了晶界偏析的热力学。在 BCC Fe 中产出的 Zn 偏析能谱揭示了 Fe 晶界 Zn 的平均偏析浓度与宏观 Zn 含量、温度和晶界原子分数之间的定量关系。它表明 Fe 晶界处 Zn 偏析的热力学驱动力很强，这与晶界能量直接相关：高能晶界可以容纳大量的 Zn 原子，而低能晶界对 Zn 表现出一定程度的排斥。从动力学上讲，Zn 更容易通过扩散而不是穿透进入晶界。尽管如此，Zn 渗透引起的晶界脆化比 Zn 扩散引起的晶界脆化更严重。脆化效应通常随着晶界处 Zn 浓度的增加而线性增加。总之，它表明 Zn 晶界偏析诱导的钢中的 LME 是 Zn 熔体渗透和 Zn 原子固态扩散的综合结果。