H-induced decohesion across the grain boundary and H-enhanced vacancy activity in metals

W. T. Geng, A. J. Freeman, G. B. Olson, Y. Tateyama, T. Ohno

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Citation (Scopus)

Abstract

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 calculations on the energetics of interstitial H, vacancy, and H-monovacancy complexes (VHn) in Fe have shown that the predominant complex under ambient condition of H pressure is VH2, not VH 6 as previously suggested by effective-medium theory calculations. The linear structure of VH2, 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.

Original languageEnglish
Title of host publication11th International Conference on Fracture 2005, ICF11
Pages3305-3310
Number of pages6
Publication statusPublished - Dec 1 2005
Event11th International Conference on Fracture 2005, ICF11 - Turin, Italy
Duration: Mar 20 2005Mar 25 2005

Publication series

Name11th International Conference on Fracture 2005, ICF11
Volume5

Other

Other11th International Conference on Fracture 2005, ICF11
CountryItaly
CityTurin
Period3/20/053/25/05

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ASJC Scopus subject areas

  • Geotechnical Engineering and Engineering Geology

Cite this

Geng, W. T., Freeman, A. J., Olson, G. B., Tateyama, Y., & Ohno, T. (2005). H-induced decohesion across the grain boundary and H-enhanced vacancy activity in metals. In 11th International Conference on Fracture 2005, ICF11 (pp. 3305-3310). (11th International Conference on Fracture 2005, ICF11; Vol. 5).