Anisotropic mechanical properties of graphene/copper composites with aligned graphene

The isotropic mechanical properties of graphene/metal composites with randomly distributed graphene have been extensively studied. However, the anisotropic mechanical properties of aligned graphene/metal composites in both in-plane and through-plane directions have not yet been reported. Herein, we attempted to align graphene nanoplatelets (GNPs) in the Cu matrix via a vacuum filtration method followed by spark plasma sintering. It was demonstrated that a fairly good GNP alignment was achieved in the composites, leading to the prominent anisotropic mechanical properties with in-plane tensile strength and elongation significantly outperforming through-plane ones. Nevertheless, only moderate in-plane strength enhancement (26% at 10 vol% GNPs) was obtained in the composites, and this enhancement was further diminished to -7.1% with increasing GNP fraction to 20 vol%, which was attributed primarily to the weak GNP-Cu interface that is bonded by mechanical interlocking. Furthermore, the anisotropic mechanical behavior of aligned GNP/Cu composites was proposed to originate from the different interface failure modes of 'GNP slippage' and 'GNP peer-off with the load parallel and perpendicular to the alignment direction, respectively. Therefore, further improvement of interfacial bonding strength will be an important step towards the optimization of the anisotropic mechanical properties of aligned graphene/metal composites.