Density, microstructure and mechanical property of large-scale C/C composites prepared by thermal gradient CVI

2D-C/C composites with the dimension of Φ80mm×400mm were prepared rapidly by thermal gradient CVI within 104 hours. Their density reached 1.74g/m ³ and the density difference was less than 0.04g/cm ³. The pyrocarbon microstructure changed from RL to RL+SL, and then to SL along radial direction. These changes were attributed mainly to the difference of gas concentration and temperature gradient at every micro-zone during chemical vapor infiltration. After heat-treatment at high temperature, the space among layers of pyrocarbon enlarged and residual thermal stress was freed, which could lead to cracks formed in matrix. The flexural property of composites decreased with increasing heat-treatment temperature and the fracture mode changed from the brittleness to pseudo-plastic. Carbon particulars between pyrocarbon laminas can increase the flexural strength by particular reinforcement.