Hydrogen trapping in helium-implanted W and W-Ta alloy: First-principles approach

We reveal the interaction of H with He in pure W and W-Ta alloy based on first-principles calculations. We show a strong attraction between H and He in both systems that drives H segregation towards He. The substitutional He and tetrahedral interstitial H defects in W-Ta alloy are more energetically favorable than pure W due to the decreased electronic density of the replaced Ta atom. Moreover, 1 He-Vac complex in both systems can trap as many as 12 H atoms. Based on the calculated formation energy of Hn-He-Vac complexes, the H3-He-Vac has the lowest formation energy in both systems. We believe that such understanding is generally applicable for H bubble formation in metals and metal alloys.