Dislocation nucleation from Zr-Nb bimetal interfaces cooperating with the dynamic evolution of interfacial dislocations

The nucleation of lattice dislocations (LDs) from bimetal interfaces is critical to the interface-mediated deformation and strengthening mechanism in nanoscale multilayered metallic composites. Such nucleation not only depends on external loadings but also closely correlates with interfacial dislocation (ID) networks and their dynamic evolution. In this study, we focused on LD nucleation cooperating with IDs dynamic evolution from Zr/Nb bimetal interfaces following Pitch-Schrader and Burgers orientation relationships. To mimic the cross interactions between Zr and Nb atoms in molecular dynamic simulations, an empirical embedded-atom method potential was developed. The automatic Nye tensor analysis method was employed to directly identify the characteristics of IDs, which showed that: (1) many segments with obvious directivity, named main segments, were regularly distributed within IDs networks; and (2) main segments were connected by several atomic steps at regions where IDs intersected with each other. These characteristics have demonstrated, for the first time, the significant details of hcp/bcc interfaces. The further analyses of IDs dynamic evolution as LDs nucleation indicated: (1) the nucleation, which preferred at or by IDs intersections, is attributed to the flexible movement of atomic steps, by which the line orientations of ID segments at intersections can be adaptively altered to be parallel to the traces of LDs glide planes; (2) the weakened block effect of main segments in low strain concentrations is responsible for the unexpected nucleation across main segments in a direction which largely deviates from main segments. This investigation gives helpful understanding of the interface-mediated deformation in not only Zr/Nb but also other hcp/bcc (especially hcp crystals with low c/a ratios) nanolayered composites, and can satisfy the renewed interest in the fundamental scientific field of dislocations-interfaces interactions.