Helium behaviors at Mn6Ni16Si7 precipitate in α-Fe: Insights from ab initio modeling

Abstract G-phase and helium (He) are key factors for the mechanical properties degradation in stainless steels under irradiation. In this study, the stability of He atoms inside Mn6Ni16Si7, α-Fe and at α-Fe/Mn6Ni16Si7 interface are systemically studied by first principle calculations. It is shown that He atoms are most stable in Mn6Ni16Si7, followed by α-Fe/Mn6Ni16Si7 interface and α-Fe. In Mn6Ni16Si7, He atoms tend to be sparsely distributed at independent interstitial positions. The Ni vacancy can readily form in Mn6Ni16Si7, and Ni monovacancy can trap up to nine He atoms. This result suggests the Ni vacancies could be efficient sinks for He atoms inside Mn6Ni16Si7. The behaviors at the α-Fe/Mn6Ni16Si7 interface indicate that He atoms prefer to rest at interface in supercell and facilitate nearby vacancy generation, which contributes to the embrittlement of the material.