Interactions between glide dislocations and parallel interfacial dislocations in nanoscale strained layers

Plastic deformation in nanoscale multilayered structures is thought to proceed by the successive propagation of single dislocation loops at the interfaces. Based on this view, we simulate the effect of predeposited interfacial dislocation on the stress (channeling stress) needed to propagate a new loop parallel to existing loops. Single interfacial dislocations as well as finite parallel arrays are considered in the computation. When the gliding dislocation and the predeposited interfacial array have collinear Burgers vectors, the channeling stress increases monotonically as the density of dislocations in the array increases. In the case when their Burgers vectors are inclined at 60°, a regime of perfect plasticity is observed which can be traced back to an instability in the flow stress arising from the interaction between the glide dislocation and a single interfacial dislocation dipole. This interaction leads to a tendency for dislocations of alternating Burgers vectors to propagate during deformation leading to nonuniform arrays. Inclusion of these parallel interactions in the analysis improves the strength predictions as compared with the measured strength of a Cu-Ni multilayered system in the regime where isolated glide dislocation motion controls flow, but does not help to explain the observed strength saturation when the individual layer thickness is in the few nanometer range.