Molecular dynamics simulation of hydrogen defect interaction and bubble growth in tungsten

Molecular dynamics (MD) simulations were performed to investigate the H-defect interaction in W using an analytical bond-order potential for W-H system. We first investigated the H-H interaction in W. The binding energies between H and H cluster are shown to be very small. As a result, H bubbles can not form spontaneously by self-trapping. Then we investigated the interaction between H and W self-interstitial atoms (SIAs). Although the binding energies between H atoms and small H-SIA clusters are positive, these interactions are still not strong enough for the formation of large H-SIA clusters. Finally, we analysed the binding energies of a H, a vacancy and a self-interstitial W to a H-vacancy cluster in W, respectively. The binding energies depend on the ratio of H to vacancy. The binding energies of a H atom and a self-interstitial W atom to a H-vacancy cluster both decrease as the ratio increases, while the binding energy of vacancy to H-vacancy cluster increases as the ratio increases. On the basis of these results, we conclude that H bubble formation needs a high concentration of H atoms in W, and propose a initial H bubble formation and growth process. (author)