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Abstract

The embrittlement of metals by H is a long-standing problem, whose underlying mechanisms are still largely unclear. Here we consider the atomistic basis of the HELP mechanism, which asserts that H mobilises dislocations by shielding elastic dislocation-dislocation interactions.
Using a combination of density-functional theory calculations, semiempirical EAM potentials and an effective lattice gas Hamiltonian we determine the effect of H on the stress field around edge dislocations in fcc metals. The density of the H distribution around the dislocation core is determined by the H-H interaction: weak H-H interactions give rise to a dilute H distribution, while attractive H-H interactions entail a dense H distribution. The stress field around the dislocation in the presence of a dilute and a dense H distribution is used to critically discuss the H-induced shielding effect postulated by the HELP mechanism.