The behaviors of helium atoms in tantalum, rhenium and osmium

摘要: We present systematic first-principles studies of occupancy, diffusion, and segregation of He atoms, as well as underlying evolution mechanism of He clusters in Ta, Re and Os precipitates to help to understand the effect of alloying solutes on He retention and bubble formation. It is found that single He atom prefers tetrahedral (T) site in Ta and basal octahedral (BO) site in Re and Os. Single He atom prefers the diffusion path from one T site to the closest T site in Ta, and the diffusion path from one BO site to the next BO site passing an octahedral site along $\langle$0001$\rangle$ direction in Re and Os. The diffusion of single He atom in Ta, Re and Os is relatively difficult than that in W. He atoms are energetically favorable to segregate at interstitial sites forming He$_{n}$ clusters in Ta, Re and Os, and form close-packed He monolayer structure between (110) planes in Ta. The binding strength of He$_{n}$ cluster in Ta, Re and Os is relatively small than that in W (W>Os>Re>Ta). Compared with interstitial sites, He atoms are more energetically favorable to aggregate in vacancy cluster forming VacmHen. The binding strength order of VacmHen cluster in the systems obeys W>Os>Re>Ta. We thus expect that the presence of Ta and Re may contribute to reduce He retention and bubble formation in W.