Synergistic effect of helium and hydrogen for vacancy-like defects in pure Fe and Fe9Cr alloy

Abstract

A synergistic effect between the helium and hydrogen elements exists in fusion reactors materials. To explore its microscopic mechanism, this paper meticulously investigates the H and He action for vacancy-like defects in pure Fe and Fe9Cr alloys by using first-principles calculations. The He and H vacancy-like defects were performed within atomistic simulations in body-centered cubic Fe and Fe9Cr alloys. Via analyzing the structures of the clusters, we find that He atoms in the VacHenHm clusters are more energetically favorable to occupy the center of the vacancy and the H atoms will attach to the free surface. Based on the comprehensive analysis of the vacancy trapping energy, vacancy formation energy, formation volumes, and the electron density maps, He elements play a more dominant role within the H/He synergistic effect, while H elements aggravate the bubble growth. There is no evident chemical bonding between He and H atoms. Concerning the Cr atoms, the Cr-He possesses the strongest repulsive energy within the considered diatomic molecules. The Cr element could weaken the aggregation and reduce the diffusion barriers of the vacancies, thus inhibiting the growth of vacancy-like defects to some extent. These results would help to provide insights into the synergistic effect of He and H for vacancy-like defects in Fe9Cr alloy.