Electronic effects of sulphur in nickel

Abstract

This paper reports the first study employing detailed electronic structure calculations to investigate a model of grain boundary embrittlement. The results show that adding sulphur to a cluster of nickel atoms causes strong bonds to be formed between the sulphur atom and the nickel atoms nearest to it, while simultaneously weakening bonds between these nickel atoms and their neighbouring nickel atoms in the cluster. As a consequence one can suggest that sulphur forms very strong bonds within the plane of the boundary but weakens metal–metal bonds perpendicular to this plane. Although, for the present, the results can be considered only as suggesting one possible embrittling mechanism, they do demonstrate the insight which such calculations can provide into this very central question of grain boundary embrittlement.