The electronic origin of solid solution softening in body-centered cubic Mo alloys was investigated within the framework of a combined approach that included atomistic dislocation modelling with first-principles parametrization of interatomic interactions. The softening additions were found to change locally the chemical bonding which resulted in a decrease in the generalized stacking fault energy and atomic row shear resistance. Using the atomic row model, it was shown that the isotropic core of the screw dislocation in Mo tended to a "split" (planar) core upon alloying with softer solutes (Re, Os, Ir, Pt). The generalized Peierls-Nabarro model for a non-planar core was used to link the reduction in generalized stacking fault energy with the enhancement of double kink nucleation and dislocation mobility. The results appeared to explain the experimental dependence of the alloying effect upon the atomic number of the addition and to provide an understanding of the electronic basis of solid-solution softening in Mo alloys.

Solid Solution Softening in BCC Mo Alloys - Effect of Transition-Metal Additions on Dislocation Structure and Mobility. N.I.Medvedeva, Y.N.Gornostyrev, A.J.Freeman: Physical Review B, 2005, 72[13], 134107 (9pp)