We have used TEM to study the microstructure of friction surface of carbon fibre/carbon-silicon carbide composites brake discs after multi braking stop by using organic pads. A friction surface layer was developed consistently on the top of Si regions of the composites, but inconsistently on that of SiC and C. Inside the layer, amorphous silicon/silicon oxides appeared extensively with various non-metallic and metallic crystallites dispersed inside with sizes ranging from a few nanometers to several microns. A coherent interface between the friction layer and the composite surface was established under the braking conditions, whilst its sustainability varied notably in SiC and C regions. Microcracking near the friction surface appeared in SiC and C /C regions largely due to the extensive ductile deformation of SiC and weak interfaces between C and C . Material joining mechanisms were discussed to enlighten the friction transfer layer development on the surface of the composite discs
