Raman spectroscopy investigation of structural and textural change in C/C composites during braking

The microstructure and texture of C/C composites with a resin-derived carbon, a rough laminar (RL) pyrocarbon and a smooth laminar pyrocarbon, before and after braking tests, were investigated by Raman spectroscopy. The full width at half maximum (FWHM) of the D-band indicates the amount of defects in the in-plane lattice, while the G-to-D band intensity (peak area) ratios (I _G/I _D) is used to evaluate the degree of graphitization. The results show that the FWHM of D-band of sample with RL pyrocarbon changes greatly from 36 cm⁻¹ to 168 cm⁻¹ after braking tests, which indicates that a large number of lattice defects are produced on its wear surface. However, the graphitization degree of resin-derived carbon sample rises significantly, because the I _G/I _D increases from 0.427 to 0.928. Braking tests under normal loading conditions, involving high temperature and high pressure, produce a lot of lattice defects on the wear surface, and induce the graphitization of the surface. Sample with RL pyrocarbon having a low hardness is easy to deform, and has the most lattice defects on the wear surface after braking. While raw materials with resin-derived carbon have the lowest graphitization degree which rises greatly during braking.