Influence of ratio of multi-walled carbon nanotubes and graphene on microstructure and mechanical properties of copper-graphite composites fabricated by spark plasma sintering

Copper-graphite composites synergetic reinforced by nano-carbon (multi-walled carbon nanotubes (MWCNTs), graphene nanoplatelets (GNPs)) and ceramic particle reinforced phases (Al2O3 particles and hexagonal boron nitride (HBN)) with alloying elements were fabricated through Spark Plasma Sintering for friction material. The surface modification of MWCNTs and GNPs treated with gallic acid and rutin solutions with ultrasonic treatment can improve the dispersibility. The interfacial bonding between the matrix and the reinforcing phase in the composites was mainly mechanical, and the diffusion layer can be observed. The content of MWCNTs and GNPs remained 1 wt.%; as the proportion of MWCNTs increased, the mechanical properties of nano-carbon and ceramic particles reinforced Cu-graphite composites gradually increased. With the content of 0.8 wt.%MWCNTs-0.2 wt.%GNPs, the composites had the best performance, and the relative density, hardness and compressive strength were 96.01%, 42.75 HV and 202.37 MPa, respectively. According to the morphology of compression fracture, the fracture type was a brittle fracture. It can be determined that the strengthening mechanisms of the composites were mainly load transfer, particle strengthening and fine grain strengthening.