Differences in mechanical behaviors and characteristics between natural graphite/copper composites and carbon-coated graphite/copper composites

Natural graphite/copper (NG/Cu) composites and carbon-coated graphite/copper (CCG/Cu) composites were prepared via powder metallurgy by using electrolytic copper powder, natural graphite and phenolic resin as raw materials. The mechanical deformation behaviors and characteristics and the structure evolution of the two composites under the actual force form during friction (bending and compression) were investigated in detail. The results show that CCG/Cu composites exhibit ductile fracture and can withstand higher loads in the bending test, which is due to a high compactness and continuity matrix and a uniform distribution of intact CCG, while NG/Cu composites show brittle fracture. Owing to the low compactness and continuity matrix and the incomplete NG structure of NG/Cu composites themselves, the deflection and tear of matrix, the deflection and lamellar layers slide of NG and some NG connection occur from deformation to failure in the compression test, and these structural defects are exacerbated until the main crack penetrates through the sample, leading to failure. Although CCG/Cu composites eventually fail in the compression test, carbon coating with phenolic resin on natural graphite effectively delays the deformation and failure and improves the compression strength of CCG/Cu composites. This work provides a reliable mechanical analysis for the failure mechanism of graphite/copper composites during friction.