Hydrogen-promoted grain boundary embrittlement and vacancy activity in metals:: Insights from ab initio total energy calculatons

被引:43
作者
Geng, WT [1 ]
Freeman, AJ
Olson, GB
Tateyama, Y
Ohno, T
机构
[1] Northwestern Univ, Dept Phys & Astron, Evanston, IL 60208 USA
[2] Northwestern Univ, Dept Mat Sci & Engn, Evanston, IL 60208 USA
[3] Natl Inst Mat Sci, Tsukuba, Ibaraki 3050047, Japan
关键词
hydrogen embrittlement; grain boundary embrittlement; vacancy activity; ab initio calculation;
D O I
10.2320/matertrans.46.756
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
The rapid diffusion of H in metals permits an easy segregation to the grain boundary and an easy trapping to the vacancy. H-induced intergranular embrittlement in metals such as Fe and Ni is generally a result of coalition of segregated H and other embrittling impurities at the grain boundary. Ab initio total energy calculations based on the density functional theory have shown that H alone can also weaken the cohesion across the grain boundary. The stronger binding of H with a free surface than with a grain boundary, which results in grain boundary embrittlement according to the Rice-Wang theory, can be ascribed to its monovalency. New tensile experiments point to a H-enhanced vacancy contribution to the increased susceptibility of steel to H embrittlement. Ab initio density functional calculations on the energetics of interstitial H, vacancy, and H-monovacancy complexes (VacHn) in bee Fe have shown that the predominant complex under ambient condition of H pressure is VacH(2), not VacH(6) as previously suggested by effective-medium theory calculations. The linear structure of VacH(2) clusters, a consequence of repulsion between negatively charged H atoms, facilitates the formation of linear and tabular vacancy clusters and such anisotropic clusters may lead to void or crack nucleation on the cleavage planes. On the other hand. the H-induced increase of vacancy cluster formation energy is a support of the experimentally observed enhancement of dislocation mobility in the presence of H, which, through the mechanism of H-enhanced localized plasticity. makes fracture easier.
引用
收藏
页码:756 / 760
页数:5
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