TY - JOUR
T1 - Hydrogen-promoted grain boundary embrittlement and vacancy activity in metals
T2 - Insights from ab initio total energy calculatons
AU - Geng, Wen Tong
AU - Freeman, Arthur J.
AU - Olson, Gregory B.
AU - Tateyama, Yoshitaka
AU - Ohno, Takahisa
N1 - Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2005/4
Y1 - 2005/4
N2 - 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.
AB - 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.
KW - Ab initio calculation
KW - Grain boundary embrittlement
KW - Hydrogen embrittlement
KW - Vacancy activity
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U2 - 10.2320/matertrans.46.756
DO - 10.2320/matertrans.46.756
M3 - Review article
AN - SCOPUS:20844453209
VL - 46
SP - 756
EP - 760
JO - Materials Transactions
JF - Materials Transactions
SN - 0916-1821
IS - 4
ER -