Strengthening mechanisms of graphene in copper matrix nanocomposites: A molecular dynamics study

To clarify the strengthening mechanism of coated/embedded graphene in metal matrix nanocomposites, nanoindentation responses of graphene-coated/embedded copper nanocomposites are investigated using molecular dynamics simulations, with the consideration of indentation force-displacement relation, stress distribution, evolution of microstructure and dislocation, and elastic recovery. Results show that two mechanisms, graphene layer bearing surface tensile stress disperses the contact stress and blocks the propagation of dislocations, contribute to the enhanced hardness and improved load bearing capacity, but one is often dominant for different nanocomposites. The former dominates in graphene-coated structure while the latter dominates in graphene-embedded structure, and the reinforcement is more obvious in the coated structure. The graphene delays the plastic deformation of matrix, and its elastic recovery is boosted due to the stress homogenization effect. The embedded graphene promotes the stress concentration and accelerates the plastic deformation of up Cu film, weakening its width elastic recovery. The observations will provide a practical guide for the mechanical optimization and design of metal-graphene nanocomposites.