Effect of helium and vacancies in a vanadium grain boundary by first-principles

We present the preferential site, segregation and embrittlement behavior of helium (He) and vacancies in a vanadium (V) ∑3 (1 1 1) [11¯0] grain boundary (GB) by first-principles calculations. Energetically, He prefers to occupy interstitials rather than substitutional sites at the GB, and segregate to the GB with a driving force of 0.16 eV. Vacancy formation in GB is considerably easier than in bulk regardless of He presence or no for V metal, similar to the behavior of vacancy in Fe and W metals. He acts as a strong embrittler at the V GB with embrittlement energy of 2.80 eV, similar to He behaviors at the GBs of Fe and Ni metals. He segregation weakens bond strength between surrounding V atoms, leading to degradation of GB strength. The present results provide a useful reference for He effects on the mechanical properties of the GB.