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

Wen Tong Geng, Arthur J. Freeman, Gregory B. Olson, Yoshitaka Tateyama, Takahisa Ohno

Research output: Contribution to journalReview article

33 Citations (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 density functional calculations on the energetics of interstitial H, vacancy, and H-monovacancy complexes (VacHn) in bcc Fe have shown that the predominant complex under ambient condition of H pressure is VacH2, not VacH6 as previously suggested by effective-medium theory calculations. The linear structure of VacH2 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.

Original languageEnglish
Pages (from-to)756-760
Number of pages5
JournalMaterials Transactions
Volume46
Issue number4
DOIs
Publication statusPublished - Apr 1 2005

Keywords

  • Ab initio calculation
  • Grain boundary embrittlement
  • Hydrogen embrittlement
  • Vacancy activity

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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