从原子水平揭示氢如何使金属遭受破坏

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氢气对金属的化学力学削弱作用已有大量观察报道，但其在原子尺度上的作用机理仍不清楚。确定金属晶界处的所有氢吸收位点可对金属失效过程进行定量预测。由佐治亚理工学院的Ting Zhu领导的国际研究团队发展了一种方法，对金属镍按其晶格几何结构划分成原子级多面体堆积单元，以原子的多面体堆积单元来划分晶界，由此获得氢在晶界处的吸附位点，进而从原子水平对镍的晶界氢脆化加以研究。通过对晶界的原子水平模拟发现，氢通过电子效应与镍结合，并在较高温度下恶化和破坏晶界；晶界强度降低不仅取决于氢嵌入镍晶界的位置，也取决于晶界处的氢浓度。该研究还进一步分析了局部电子密度对氢吸附能的影响，揭示了晶界氢脆化的物理极限。上述用于量化氢脆化导致金属失效的计算模拟框架将有助于减缓含氢压力容器和管道的失效。该文近期发表于npj Computational Materials 3:28 (2017); doi:10.1038/s41524-017-0031-1; 标题与摘要如下，论文PDF文末点击阅读原文可以获取。

Hydrogen embrittlement of grain boundaries in nickel: an atomistic study (镍晶界的氢脆化：原子水平上的研究)

Shan Huang, Dengke Chen, Jun Song, David L. McDowell & Ting Zhu

The chemomechanical degradation of metals by hydrogen is widely observed, but not clearly understood at the atomic scale. Here we report an atomistic study of hydrogen embrittlement of grain boundaries in nickel. All the possible interstitial hydrogen sites at a given grain boundary are identified by a powerful geometrical approach of division of grain boundary via polyhedral packing units of atoms. Hydrogen segregation energies are calculated at these interstitial sites to feed into the Rice–Wang thermodynamic theory of interfacial embrittlement. The hydrogen embrittlement effects are quantitatively evaluated in terms of the reduction of work of separation for hydrogen-segregated grain boundaries. We study both the fast and slow separation limits corresponding to grain boundary fracture at fixed hydrogen concentration and fixed hydrogen chemical potential, respectively. We further analyze the influences of local electron densities on hydrogen adsorption energies, thereby gaining insights into the physical limits of hydrogen embrittlement of grain boundaries. 

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