Multi-layer graphene/copper composites: Preparation using high-ratio differential speed rolling, microstructure and mechanical properties

The possibility of using multi-layer graphene (MLG) particles as reinforcement for enhancing the mechanical properties of Cu matrix composites was explored. The combination of ball milling and high-ratio differential speed rolling (HRDSR) techniques was utilized to fabricate the 0.5 and 1 vol.% MLG/Cu composites. In the HRDSR-processed composites, the nanosized MLG particles with 5–15 nm in diameter were dispersed densely and uniformly in the grain interiors of Cu matrix with a preferred crystallographic relationship of 〈1 1 1〉Cu//〈0 0 0 1〉MLG to the matrix. The conventionally rolled composites with the same contents of MLG, however, contained much lower densities of nanosized MLG particles. This result indicates that the large shear strain induced during HRDSR accelerated breaking up of MLGs into nanosizes and enhanced their dispersion in the matrix. The strength improvement through the addition of MLGs was obvious when HRDSR was used, but it was negligible when conventional rolling was used. The strengthening gained through the homogeneous dispersion of high-density nanosized MLG particles in the HRDSR-processed composites was attributed to Orowan strengthening. This finding is different from the HRDSR-processed carbon-nanotube (CNT)/Cu composites studied in our previous work, in which the grain-size reduction through the addition of CNTs was the major contribution to the strengthening effect.