Microstructures and mechanical properties of carbon/carbon composites prepared by impulse forced flow thermal gradient chemical vapor infiltration

Felt-based C/C composites were fabricated by an impulse forced flow thermal gradient chemical vapor infiltration technique The micro-morphologies and textural characteristics of the pyrocarbon and fracture surfaces were observed by polarized light microscopy and SEM. The mechanical properties of the composites were tested by bending experiments. Results showed that the density of the composites could be up to 1.7 g/cm³ after 100 h densification at 1000°C-1250°C. Further heat treatment at 2300°C was carried out following densification. The flexural strength of the composites could reach 125.4 MPa with a deflection of 0.61 mm. The advantages of this technique were a high densification rate, uniform density and good mechanical properties. Densification temperature had a great impact on the microstructure. A higher temperature favored rough layer pyrocarbon while a lower temperature favored for smooth layer pyrocarbon, but a mixture was obtained in most cases because of complicated densification conditions.