MOLECULAR-ORBITAL APPROACH TO THE CHEMICAL BONDING AT GRAIN-BOUNDARY IN GAMMA'-NI3AL

The nature of chemical bonding at grain boundary in gamma'-Ni3Al has been analyzed by extended Hueckel molecular orbital method in order to investigate the intrinsic brittleness of grain boundary and the effect of doping element for enhancing ductility of polycrystalline gamma'-Ni3Al. For doping elements, B, C, P and S positioned at the grain boundary have been examined and following results are concluded. (1) Brittleness of gamma'-Ni3Al grain boundary attributes to the coulombic repulsive force between same atoms that arrange adjacently at the grain boundary. In particular, Al atom repels strongly against each other. (2) Boron can bind with both Ni and Al without decreasing bonding energy between constituent atoms, which would lead to improve the strength of grain boundary.