On the role of weak interfaces in blocking slip in nanoscale layered composites

Layered composites of Cu/Nb achieve very high strength levels when the individual layer thicknesses are 1-10 nm, attributable to the interfaces acting as barriers to slip. Atomistic models of Cu/Nb bilayers were used to explore the origins of this resistance. The models clearly show that dislocations placed near an interface experience an attraction toward the interface, regardless of the sign of the Burgers vector or the material in which it is placed. This attraction is caused by shear of the interface induced by the stress field of the dislocation. Furthermore, the dislocation, upon reaching the interface, is absorbed by it in the sense that the core spreads within the interface. We develop a model, using a fractional dislocation approach, which provides an estimate of the strength of the attraction as a function of distance from the interface and also the dependence of the interaction on the type of dislocation. A screw dislocation is much more effective in shearing the interface, and the resulting attractive forces on screws are larger than for edge dislocations.