Effect of grain boundary structures on the behavior of He defects in Ni: An atomistic study

We investigated the effect of grain boundary structures on the trapping strength of He_N (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 He_N 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 He_N defect increases with the defect size. Moreover, the binding strength of the He_N defect to the $\Sigma 3\left(1\overline{1}2\right)\left[110\right]$ grain boundary becomes much weaker than that to other grain boundaries as the defect size increases. (paper)