Morphologies, microstructure and mechanical properties of 2D carbon/carbon composites during the CVI densification process

The processing-structure-properties relationship of two-dimensional carbon/carbon (C/C) during the chemical vapor infiltration (CVI) process was investigated. The weight gain, density, porosity, flexural strength and flexural modulus of CC composites were measured as a function of CVI processing time up to 72 hours. Three regions corresponding to different microstructures were observed in the CVI densification process. In region I, the highest weight-gain rate was observed due to the largest surface area available for the deposition of PyroC. The improvement of flexural strength and modulus is most significant in this region due to the closing of microcracks in the porous CC composites. In region II, the open pores are closed from small to large size due to PyroC deposition. In region III, the open pores are almost closed and exhibit the lowest weight-gain rate; in this region, the improvement of density and flexural strength is insignificant. However, the presence of new cracks in the final stage of the CVI process decrease the flexural modulus of CC composites.