First-principles investigation of energetics and site preference of He in a W grain boundary

We perform first-principles calculations based on density functional theory to investigate energetics and site preference of He in a bcc-W Sigma = 5 grain boundary (GB). The segregation energy is calculated to be -1.37 eV, indicating that He prefers to segregate in the W GB. The formation energy of He in the W GB is positive and thus He is quite hard to dissolve in the W GB, similar to its behavior in the bulk. Because of its closed-shell electronic structure, He is shown to preferably occupy either interstitial or substitutional site with larger space provided by the GB, changing the GB electronic structure. Moreover, segregation of He gives rise to the W GB expansion. These structure variations can have a large effect on the mechanical properties of the W GB. (C) 2009 Elsevier B.V. All rights reserved.