材料期刊网

The effects of B, C, N, O, H, P and S impurities on the Ni/Ni3Al interface cohesion have been investigated by employing first-principles electronic structure calculations based on the discrete variational method. The binding energy, bond order, difference electron density, orbital occupations and density of states have been calculated to study the impurity-induced changes in the energetics and electronic structure. The impurities promote the Ni/Ni3Al interface cohesion and prefer to occupy the interface interstitial sites in the order S < P < H < O < N < B < C. The impurity-nickel covalent-like bonds form mainly due to impurity-p/Ni-d hybridization (except H-s/Ni-p hybridization in the H case). Meanwhile, the Ni-Ni bonding becomes weaker because of charge depletion on Ni atoms and bond misorientation resulting from the more homogeneous electron redistribution. In the order B, C, N and O, the impurity-metal bond varies from being homopolar to being much more heteropolar with increasing ionicity percentage, which results in decreasing p-d hybridization effects. (C) 1997 Acta Metallurgica Inc.