Interstitial hydrogen enhances the mobility of some grain boundaries in tungsten

Abstract

Segregation of interstitials at a Grain Boundary (GB) is known to generally lower its mobility. This phenomenon, called ‘solute-drag,’ has important ramifications on the process of recrystallization and microstructural evolution. In this manuscript, we present predictions from molecular dynamics (MD) simulations which demonstrate that interstitial hydrogen in tungsten can in fact increase the mobility of some GBs which exhibit shear coupling. Assuming a disconnection-based mechanism, activation energies and pre-factors for disconnection nucleation are predicted from simulations of shear-coupled motion. In GBs where enhanced mobility is predicted, interstitial H reduces both the activation energy and the pre-factor for disconnection nucleation, thus effectively increasing the mobility. For GBs with diminished mobility, MD predicts that presence of interstitial H reduces the pre-factor and, in some cases, increases the activation energy. The reduction in the activation energy inferred from MD simulations are confirmed by Nudged Elastic Band calculations. Temperature-dependent structural transitions are observed for some GBs, and the effect of interstitial H is found to change with the changes in structure. The effect of interstitial H is predicted to be complex and highly variable, providing some plausible explanations for experimental observations on the recrystallization of tungsten in presence of H-loaded plasma.

The Evolution of Structural Defects under Irradiation in W by Molecular Dynamics Simulation

“…Then, the NVE ensemble (constant number of atoms, volume, and total energy) was employed to simulate the dynamic process of the incident PKA. The potential selected in this work is the embedded-atom method potential developed by Marinica [ 32 ], which was successfully applied in many previous works to investigate the defects under the irradiation of W [ 33 , 34 , 35 , 36 , 37 ]. The Open Visualization Tool (OVITO) was used for defect analysis and visualization of the simulation results [ 38 ].…”