Effects of infiltration conditions on the densification behavior of carbon/carbon composites prepared by a directional-flow thermal gradient CVI process Original Research Article

Multiple quasi three-dimensioned carbon fibre preforms with disk-like shape were simultaneously densified by a directional flow thermal gradient CVI process. The effects of infiltration conditions, including temperature (ranging from 850 to 1050 °C), temperature gradient (5 and 10 °C/mm), pressure (2.5, 5.0, 7.5 and 9.5 kPa) and the type of carrier gas (N2 or H2), on the densification behavior of the resultant carbon/carbon composites were investigated. The results showed that lower temperatures (below 900 °C), a larger temperature gradient and higher pressure are favorable for higher average bulk density and homogeneous infiltration. Carbon/carbon composites disks with an average bulk density of 1.78 g/cm3 were achieved in one CVI cycle at a total pressure of 9.5 kPa. It was also found that adding N2 carrier gas has no pronounced influence on the densification of the preforms. As compared to N2, H2 had positive effects on the densification of the preforms for temperatures above 900 °C, but it had negative effects on the densification when the control temperature was as low as 850 °C.