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Screw dislocations in bcc metals display non-planar cores at zero temperature which result in high lattice friction and thermally-activated strain rate behavior. In bcc W, electronic structure molecular statics calculations reveal a compact, non-degenerate core with an associated Peierls stress between 1.7 and 2.8 GPa. However, a full picture of the dynamic behavior of dislocations can only be gained by using more efficient atomistic simulations based on semiempirical interatomic potentials. In this paper we assess the suitability of five different potentials in terms of static properties relevant to screw dislocations in pure W. Moreover, we perform molecular dynamics simulations of stress-assisted glide using all five potentials to study the dynamic behavior of screw dislocations under shear stress. Dislocations are seen to display thermally-activated motion in most of the applied stress range, with a gradual transition to a viscous damping regime at high stresses. We find that one potential predicts a core transformation from compact to dissociated at finite temperature that affects the energetics of kink-pair production and impacts the mechanism of motion. We conclude that a modified embedded-atom potential achieves the best compromise in terms of static and dynamic screw dislocation properties, although at an expense of about ten-fold compared to central potentials.

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The trapping and mobility of hydrogen in nanostructured tungsten grain boundaries (GBs) have been studied by combining experimental and density functional theory (DFT) data. Experimental results show that nanostructured W coatings with a columnar grain structure and a large number of (1 1 0)/(2 1 1) interfaces retain more H than coarsed grained W samples. To investigate the possible influence of GBs on H retention, a complete energetic analysis of a non-coherent W(1 1 0)/W(1 1 2) interface has been performed employing DFT. Our results show that this kind of non-coherent interface largely attracts point defects (both a H atom and a metallic monovacancy separately) and that the presence of these interfaces contributes to a decrease in the migration energy of the H atoms with respect to the bulk value. When both the W monovacancy and H atom are introduced together into the system, the HV complex becomes the most stable configuration and one of the mechanisms explaining the H retention in the radiation damaged GB observed experimentally.