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

The atomic and the electronic structures of the Sigma 5 (210) [001] tilt gr ain boundary in Ni3Al, with and without a hydrogen impurity, have been calc ulated using the full potential linearized-augmented plane-wave method. The strain held normal to the boundary plane and the excess grain boundary vol ume are calculated and compared with the results obtained using the embedde d-atom method (EAM). The interlayer strain normal to the grain boundary osc illates with increasing distance from the grain boundary. The bonding charg e distributions suggest that bonding in the boundary region is different fr om that in the bulk. Total-energy calculations show that the hydrogen impur ity prefers to occupy interstitial sites on the Ni-rich grain boundary plan e. 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 grai n boundary energy and reduce the Griffith cohesive energy of the boundary, which indicates that hydrogen is an embrittler of the grain boundary. [S016 3-1829(98)04245-3].