Potential regulation of strength-ductility by nucleation and growth mechanisms of shear bands in heterogeneous laminates

Abstract

Shear bands (SBs) expand rapidly in hard domains and are suppressed in soft domains, effectively improving the tensile plasticity of the material. Significant evolution of SBs during elastoplastic deformation exists in heterogeneous laminates (HLs). Molecular dynamics (MD) simulation results indicate that the activities of grain boundary (GB) and dislocation jointly mediate the nucleation and growth of SBs. SBs tend to nucleate near the interface, and then grow rapidly under the promotion of GB activities and dislocation slips, resulting in a rapid increase in plastic strain gradient. Ultimately, the density and morphology of SBs determine the magnitude of the plastic strain gradient. In structures with lower layer thickness, the band-like SBs are densely distributed, which achieves higher strain gradient strengthening capability. However, the interface serves as an accumulation site for geometrically necessary dislocations (GNDs), too low a layer thickness will induce overlapping of the interface-affected-zone (IAZ), thereby weakening the strain hardening efficiency. The simulations track the nucleation and growth of SBs at the atomic scale, and discover that the structure can better balance HL's strength and ductility when the layer thickness is three times the grain size of the soft domain.