Effect of grain boundary structures on the behavior of He defects in Ni: An atomistic study**Project supported by the Program of International S&T Cooperation, China (Grant No. 2014DFG60230), the National Basic Research Program of China (Grant No. 2010CB934504), Strategically Leading Program of the Chinese Academy of Sciences (Grant No. XDA02040100), the Shanghai Municipal Science and Technology Commission, China (Grant No.

Abstract

We investigated the effect of grain boundary structures on the trapping strength of HeN (N is the number of helium atoms) defects in the grain boundaries of nickel. The results suggest that the binding energy of an interstitial helium atom to the grain boundary plane is the strongest among all sites around the plane. The HeN defect is much more stable in nickel bulk than in the grain boundary plane. Besides, the binding energy of an interstitial helium atom to a vacancy is stronger than that to a grain boundary plane. The binding strength between the grain boundary and the HeN defect increases with the defect size. Moreover, the binding strength of the HeN defect to the grain boundary becomes much weaker than that to other grain boundaries as the defect size increases.