Hydrogen embrittlement of a carbon segregated Σ5(310)[001] symmetrical tilt grain boundary in α-Fe
Hydrogen embrittlement of a carbon segregated Σ5(310)[001] symmetrical tilt grain boundary in α-Fe
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DOI：
10.1016/j.msea.2014.06.071
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发表时间：
2014-08
期刊：
影响因子：
6.4
通讯作者：
A. M. Tahir;R. Janisch;A. Hartmaier
中科院分区：
文献类型：
--
作者：
A. M. Tahir;R. Janisch;A. Hartmaier
通过从头计算晶界处不同数量的 C 和 H 原子的影响，研究了体心立方 (bcc) Fe 中 Σ 5 (310)[001] 对称倾斜晶界 (STGB) 的物理和机械性能。所得结果表明，随着C原子数量的增加，晶界能降低，并且在C完全覆盖晶界之前，偏析能仍然为负。因此，在具有足够量间隙C的bcc Fe-C体系中，C偏析态应被视为该界面的基态。晶界从头算单轴拉伸试验表明，随着 C 含量的增加，Σ 5 (310)[001] STGB 的分离功和理论强度显着增加。 C带来的内聚力的提高主要是化学效应，但机械贡献也增强了内聚力。氢的存在将C的内聚力增强机械贡献改变为脆化贡献，并且还减少了对内聚力的有益化学贡献。当氢与 C 一起存在于晶界时，对于共偏析情况，强度降低近 20%，如果 C 完全被 H 取代，则强度降低超过 25%。然而，与纯铁中 STGB 的强度相比，H 的影响可以忽略不计。因此，氢脆只能在三组分 Fe-C-H 体系中理解。
The physical and mechanical properties of a Σ 5 (310)[001] symmetrical tilt grain boundary (STGB) in body centred cubic (bcc) Fe are investigated by means of ab initio calculations with respect to the effect of a varying number of C and H atoms at the grain boundary. The obtained results show that with increasing number of C atoms the grain boundary energy is lowered, and the segregation energy remains negative up to a full coverage of the grain boundary with C. Thus, in a bcc Fe–C system with a sufficient amount of interstitial C, the C segregated state should be considered as the ground state of this interface. Ab initio uni-axial tensile tests of the grain boundary reveal that the work of separation as well as the theoretical strength of the Σ 5 (310)[001] STGB increases significantly with increasing C content. The improved cohesion due to C is mainly a chemical effect, but the mechanical contribution is also cohesion enhancing. The presence of hydrogen changes the cohesion enhancing mechanical contribution of C to an embrittling contribution, and also reduces the beneficial chemical contribution to the cohesion. When hydrogen is present together with C at the grain boundary, the reduction in strength amounts to almost 20% for the co-segregated case and to more than 25% if C is completely replaced by H. Compared to the strength of the STGB in pure iron, however, the influence of H is negligible. Hence, H embrittlement can only be understood in the three component Fe–C–H system.