Fabrication and Tribological Performance of Copper/Graphite Self-Lubricating Composites with 3D Bi-Continuous Structure

In this paper, polyurethane sponge was used as a three-dimensional continuous network structure template, and graphite slurry was uniformly coated on the surface of the polyurethane sponge skeleton by dipping to construct a graphite skeleton with a three-dimensional continuous network structure, and then populate a quantity of copper alloy powder was filled in the graphite skeleton. Then, the copper/graphite self-lubricating composites with a bi-continuous three-dimensional structure of graphite phase and metallic copper were prepared by degumming-hot pressing sintering process. The study investigated the effect of the three-dimensional bi-continuous structure on the carrying capacity and impact resistance of the material, and explored friction and wear behavior of the material under heavy load. The results showed that the enrichment state and distribution form of graphite phase could be effectively changed by three-dimensional bi-continuous structure design, and the anti-wear properties of the material under heavy load were significantly improved by the high bearing capacity of copper matrix. When the experimental load was up to 180 N and the friction pair was bearing steel, the Cu663 block and the homogeneous copper/graphite composites both showed severe wear and ‘jamming’ against with the friction pair. The test stopped due to the serious ‘jamming’ of Cu663 block and the friction pair. Although the homogeneous copper/graphite composite did not stop experiment with the friction pair ‘jamming’, its grinding depth was as high as 1.38 mm. However, the friction coefficient of the copper/graphite composites with a three-dimensional bi-continuous structure could be maintained at about 0.12 over time, and the wear scar depth was 0.16 mm. Compared to the other two composites, this material exhibited excellent long-time wear stability, the wear rate was only about 5.3×10⁻⁶ mm³/(N∙m). At the same time, the structure design greatly reduced the number of weak interfaces between graphite phase and copper matrix, and effectively utilized the ‘disproportionation’ guidance of continuous graphite on the crack propagation path and the passivation effect of metal copper on extended cracks, so that the composites maintained the high load capacity of the copper alloy and significantly improved impact resistance of the material. The bending strength of copper/graphite composites with three-dimensional bi-continuous structure was as high as 372±38 MPa (comparable to the Cu663 block), which was twice stronger than that of homogeneous copper/graphite composites. In addition, the copper/graphite composite material with a three-dimensional bi-continuous structure also had better resistance to external load impact damage, and its impact toughness was as high as 32.8±3.1 J/cm², which was 11.1 times higher than that of the homogeneous copper/graphite composites, and even 2.2 times higher than that of the Cu663 block.