Surface Change of Carbon–Carbon Composite Materials under Friction

Carbon fiber composites based on graphitized and carbonized fibers, which are used in frictional units, were investigated. Composite samples were subjected to tribological tests on an IM-58 friction machine, which simulates operating conditions of aircraft brakes. The friction surface was studied by SEM and SPM methods, material sections were studied by SEM methods. X-ray structural analysis of the samples and the study of material porosity are carried out. Features of the friction surface structure and the wear mechanisms of materials were determined. Peculiarities of changes in the near-surface layers of the composite under high contact pressures and temperatures are revealed. It was found that differences in the fibers heat treatment temperature cause differences both in the structure of the fibers themselves and in the structure of the matrix with the distribution of fibers in the volume of the material. The stiffer graphitized fibers lie nearly parallel to the friction surface, while the more flexible carbonized fibers may lie at slight angles to the working surface. A material based on graphite fibers has a double wear resistance, a lower overall porosity (12 vs. 17%) and a shallower depth of changes in the subsurface layers during friction (~34 vs. ~64 μm). The composites considered in this study are widely used as a material for the manufacturing of aircraft brake discs. The results can be used to increase the service life of aircraft brakes and improve their characteristics.