Multiscale modelling of the influence of hydrogen on dislocation junctions in bcc iron.

Multiscale modelling of the influence of hydrogen on dislocation junctions is presented by incorporating a hydrogen core force into the total nodal force. The hydrogen core force arises due to hydrogen induced change in dislocation core energy, which was calibrated at the atomic scale accounting for the nonlinear inter-atomic interactions at the dislocation core, giving the model a sound physical basis. Hydrogen reduces the core energy of edge dislocations, which reduces the magnitude of the dislocation core force. We refer to this as hydrogen core force shielding, as it is analogous to hydrogen elastic shielding but occurs at much lower hydrogen concentrations. Hydrogen was found to strengthen binary junctions and promote the nucleation of dislocations from triple junctions. Simulations of microcantilever bend tests with hydrogen core force shielding showed an increase in the junction density and subsequent hardening. These simulations were performed at a small hydrogen concentration realistic for bcc iron.