Reduced Graphene Oxide-Refined Cu Matrix Composites: An Experimental and First-Principles Study

Reduced graphene oxide/copper matrix composites (RGO/Cu) are successfully fabricated via powder metallurgy methods. Composite powders of electrolytic Cu and 0.5 or 1.0 wt% graphene oxide (GO) are prepared by high-energy ball milling. The composites are then consolidated using hot-press sintering with a pressure of 22 MPa at 800 degrees C under a vacuum of 2 x 10(-2) Pa. Microstructural observations of the RGO formed from GO show that it is located along the Cu grain boundaries and CuO nanoparticles distributed inside the Cu grain. The average grain sizes are 30.11 (pure Cu), 24.75 (0.5 wt% RGO/Cu composites), and 19.66 mu m (1.0 wt% RGO/Cu composites). The Vickers hardness and tensile strengths of the RGO/Cu composites are higher than those of pure Cu. Theoretical research based on first-principles calculations shows that oxygen atoms from the decomposition of GO react with Cu to form CuO nanoparticles. This secondary phase behaves as a pin that hinders the growth of copper grains. The covalent bonding between RGO and Cu slightly limits the movement of neighboring Cu atoms. More importantly, the grain refinement mechanism is related to the RGO retarding the diffusion of Cu atoms along the interface of copper grains due to its large activation energy.