Damage of carbon–carbon composite surfaces under high pressure and shear strain

Under the influence of high contact pressure, the tribological performance of carbon–carbon composite materials essentially depends on the carbon fiber texture and on the properties of the transferred layers. In this study, employing a combination of scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS), the authors explored the friction track properties and described the role of the transferred layers in friction and wear of copper/carbon–carbon composite couples in open air of 20–30% relative humidity at room temperature. Two multidirectional carbon fiber-reinforced carbonaceous matrix materials were investigated. One of the tested composites is based on a three-directional (3D) construction consisting of multiple yarn bundles located within the structure forming, with the longitudinal fibers, a mailing texture at the surface. The other is a 2D array with a taffeta texture. The results of the tribological tests indicated that the friction coefficient and wear rate decrease when the carbon fibers exhibit a mail texture. For a 2D carbon–carbon composite, the contact surface has a rough appearance and the fiber surfaces are marked with wear grooves. Patches of scattered wear debris and worn fibers with longitudinally oriented structure are clearly visible on the contact surface of the 2D composites. The carbon matrix appears to be covered with a very granular layer made of a mixture of copper oxide and copper particles as revealed by EDS analysis. The friction track of the 3D carbon–carbon composite is covered with a layer of film-like structure debris. Again, wear grooves on the carbon fibers are observed. However, these wear grooves are relatively narrow and shallow compared with the grooves observed on the taffeta composite surface, leading to a wear rate lower in this case.