The effect of reduced graphene oxide content on the microstructural and mechanical properties of copper metal matrix composites

This study focuses on the relationship between the microstructure and the resulting mechanical and thermal properties of copper (Cu)/reduced graphene oxide (rGO) composites produced by spark plasma sintering as a function of rGO content (varying from 0 to 0.4 wt%). At the lowest rGO loading (0.025 wt%) the strength of the composite was double that of unreinforced Cu, with higher rGO fractions showing progressively lower improvements. Unexpectedly, the composites displayed a tensile yield drop (discontinuous yielding) on straining in contrast to the unreinforced Cu, ascribed to the influence of rGO nanoparticles pinning dislocations, causing a shortage of mobile dislocations. At loadings below 0.1 wt% rGO, the Cu-rGO interface was free of cracks, impurities, and voids, and the composites contained nano-sized Cu grains and well-distributed rGO nanoparticles with negligible agglomeration. However, at loadings beyond 0.1 wt% rGO, pores and rGO agglomerates were observed. The results suggest that an effective dispersion of rGO is critical, and the primary strengthening mechanisms relate to microstructure refinement, load transfer strengthening, and dislocation pinning. This work points to the efficacy of very low loadings in significantly improving strength with only a minor decrement in thermal diffusivity (<10%), opening up a number of applications.