A PSEUDOPOTENTIAL TOTAL ENERGY STUDY OF IMPURITY-PROMOTED INTERGRANULAR EMBRITTLEMENT

The authors discuss the decohesion and bond mobility models of impurity-promoted intergranular embrittlement. Both of these models are tested quantitatively using pseudopotential total energy techniques within the local density approximation. Energy calculations are for a highly simplified 'grain boundary' consisting of substitutional germanium or arsenic impurities in a crystalline aluminium lattice. They find that the germanium and arsenic impurities increase the ideal work of fracture for creating a (111) surface by up to approximately 8%. This result is inconsistent with the decohesion model of embrittlement. They also find that both impurities substantially increase the critical shear stress (by 25% for germanium and 58% for arsenic) and that arsenic impurities decrease the cleavage stress by 14%. All results are consistent with the bond mobility of intergranular embrittlement.