Intuitive Analysis of the Microtribological Behavior of Copper-Coated Graphite–Graphite/Cu Composites with High Graphite Contents

To improve the combination of graphite and copper, the friction and wear of a graphite/copper composite with a high content of graphite (50 wt %), copper-coated graphite were used to modify it. To observe the distribution law of each phase in the material and the change of composite surface structure after the friction and wear experiment, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the micro-structure, friction film, debris, and friction cross section of the composites. The results show that the large particle size of copper-coated graphite is anisotropic in the material, which helps to form a friction film with a high graphite content on the contact surface. TEM images of the friction film and debris directly reflect the structure changes of graphite and copper during friction; under normal load and shear force, interlamellar detachment and interlamellar fracture of graphite occur, and its edge is folded and crimped, resulting in the loss of an ordered state in some regions, which results in the instability of crystal lattice and the transition from an ordered to disordered state of graphite, resulting in the (002) halo ring in FFT results. Severe plastic deformation and oxidation reactions occur in copper, and copper oxides are formed, forming a high-strength and smooth oxide film in the metal-rich area and improving the wear resistance of the material. TEM images of the friction section directly show that an inverted triangular deformation zone is formed on the surface of the sample after friction and wear experiments. The edge of the deformation zone is stepped, consisting of a drag zone and an accumulation zone, and the surface of the contact zone is covered by a carbon film.