Role of interface-affected dislocation motion on the strength of Mg/Nb nanolayered composites inferred by dual-mode confined layer slip crystal plasticity

Abstract

In this work, we present a nanostructure-sensitive crystal plasticity model for the deformation response of nanolaminate composites. The model is applied to investigate the strength of Mg/Nb nanocomposites, wherein the Mg phase has either a hexagonal close-packed (HCP) or a body-centered cubic (BCC) crystal structure. To account explicitly for the effects of layer thickness and biphase interface on crystallographic slip, the model features a hardening law, called dual-mode confined layer slip (CLS). The model is applied to a suite of stress-strain measurements made on Mg/Nb nanocomposites, varying layer thickness, texture, and interface structure. Experiments show that the BCC/BCC Mg/Nb nanocomposites achieve substantially higher strength than the HCP/BCC nanocomposites. Apart from the finer layer thicknesses, the model indicates that the pseudomorphic BCC Mg phase contributes to strength by increasing the slip strengths of the 〈111〉 slip modes compared to the 〈a〉 slip modes in HCP Mg. It also suggests that the coherent interface poses less resistance to dislocation motion than the incoherent interface. It is, therefore, found that the BCC/BCC composite strength benefited from both the confinement on dislocation motion imposed by the reduced layer thickness and higher inherent strength of its BCC phase, but that it would be even higher if the interface was not a sharp coherent interface.