The effects of interstitial impurities (C, N, O) upon the strength of grain boundaries were investigated from the point of view of the electronic structure by using a discrete variational X calculation. Grain boundary structures, for the purpose of calculation, were constructed from tetrahedral clusters which included the impurity at the center (Mo4X, where X was C, N or O). The atomic cohesion, due to covalent bonding between Mo and an impurity, was estimated for each cluster. It was found to increase in the order: Mo4O - Mo4N - Mo4C. These results were in good agreement with experimental data on the effects of impurities upon the strength of grain boundaries.

K.Hiratsuka, K.Watanabe, I.Hashimoto, H.Yamaguchi: Philosophical Magazine A, 1996, 74[2], 465-76