Microstructure and mechanical properties of graphene-reinforced copper matrix composites prepared by in-situ CVD, ball-milling, and spark plasma sintering

Graphene-reinforced copper matrix composites were fabricated by in-situ chemical vapor deposition (CVD), ball-milling, and spark plasma sintering (SPS). The effects of different space structures of the graphene/copper powders imparted by ball-milling on the microstructure and mechanical properties of the composites were investigated. It was found that the in-situ CVD process gave complete coating structures of the graphene/copper powders, while subsequent ball-milling damaged the coating structure by breaking the graphene film into pieces on the copper surface. Compared to pure copper, the yield strength and tensile strength of the graphene copper matrix composites were improved by 136.6 and 16.7%, respectively, while its elongation was maintained at 35.2%. In the absence of ball-milling, the composite showed a lower tensile strength and poor electrical conductivity, with an elongation of merely 5.5%. This difference in mechanical properties originates from the different bonding behaviors between the graphene/copper powders. More specifically, weak mechanical interlocking dominates for the composite powders with the coating structure, while strong metallurgical bonding is achieved for the composite powders with uncoating structures. The strengthening mechanisms of graphene were attributed to thermal mismatch, grain refinement, load transfer, and Orowan strengthening.