First-principles studies of the ∑5 tilt grain boundary in Ni3Al

The atomic and the electronic structures of the ∑5 (210) [001] tilt grain boundary in Ni3Al, with and without a hydrogen impurity, have been calculated using the full potential linearized-augmented plane-wave method. The strain field normal to the boundary plane and the excess grain boundary volume are calculated and compared with the results obtained using the embedded-atom method (EAM). The interlayer strain normal to the grain boundary oscillates with increasing distance from the grain boundary. The bonding charge distributions suggest that bonding in the boundary region is different from that in the bulk. Total-energy calculations show that the hydrogen impurity prefers to occupy interstitial sites on the Ni-rich grain boundary plane. Hydrogen is found to reduce the bonding charge across the boundary plane. The grain boundary energy and the Griffith cohesive energy for both the "clean" and H-segregated grain boundary are calculated and compared with the available EAM results. The hydrogen impurity is found to increase the grain boundary energy and reduce the Griffith cohesive energy of the boundary, which indicates that hydrogen is an embrittler of the grain boundary.