氢原子对镍晶界位错发射的影响机制研究

氢脆是指金属材料中溶解的氢原子导致其机械性能急剧下降，从而引发材料突然断裂失效的现象。该现象严重威胁石油化工、航空航天等行业设备的服役安全性，严重限制了相关行业的发展。然而氢脆机理经历一个世纪的研究仍然未形成统一认识，其主要原因在于实验研究中难以准确表征氢原子，同时氢原子与晶界之间的纳米级相互作用机理尚未完全明晰。本文以典型氢脆金属镍为研究对象，运用分子动力学方法深入研究氢原子对晶界处位错发射的作用机理。

现有算法无法准确计算晶界处氢原子的平衡偏析分布及其对位错发射的影响。此外，分子动力学模拟中的应变率通常过高。为了解决这些问题，本研究提出了一种基于晶格的粒子群算法，用于计算氢原子在镍晶界的偏析，并对一系列<110>轴晶界构型进行了计算。计算结果表明，随着氢原子的偏析，除了Σ3(111)晶界外，其他晶界的晶界能下降，而所有晶界自由体积上升。本研究主要对Σ3(111)、Σ9(221)、Σ11(113)与Σ27(115)晶界在不同氢覆盖率下进行单轴拉伸模拟，计算结果表明随着氢覆盖率的增加，晶界处原子应力升高，晶界处位错发射能垒降低，同时晶界处存在自由体积易使得原子可以重排以发射位错，氢原子促进了晶界处的位错形核发射。本文还将基于晶格的粒子群算法与分步应变策略相结合，实现了在分子动力学尺度下对镍晶界中氢原子的动态分布进行了拉伸模拟。随着应变的增加，氢原子在Σ3(111)晶界处形成了短程有序结构。氢-短程有序结构的形成降低了氢促进局部塑性所需的临界氢浓度，是低氢浓度下发生氢脆的一个重要促进因素。

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