Monitoring unidirectional carbon/carbon composite processing by light microscopy

Unidirectional carbon/carbon composites were prepared using polyacrylonitrile-based carbon fibres and a commercial coal-tar pitch. The preparation includes a three-sequential-step process: (i) prepreging, (ii) moulding/pressing, and (iii) carbonization to 1000 °C. The effect of the process parameters including pressure, mould characteristics, and temperature and duration of pressure application on the microstructure of composites was monitored by light microscopy. Results show that the application of a pressure of 1 MPa close to the temperature of pitch solidification produces lower porosity composites. This porosity is significantly reduced when the solidification of the pitch is tempered by the introduction of a soak time of 10 h at the temperature at which pressure is applied.