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

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 degreesC), temperature gradient (5 and 10 degreesC/mm), pressure (2.5, 5.0, 7.5 and 9.5 kPa) and the type of carrier gas (N-2 or H-2), on the densification behavior of the resultant carbon/carbon composites were investigated. The results showed that lower temperatures (below 900 degreesC), 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/cm(3) were achieved in one CVI cycle at a total pressure of 9.5 kPa. It was also found that adding N-2 carrier gas has no pronounced influence on the densification of the preforms. As compared to N-2, H-2 had positive effects on the densification of the preforms for temperatures above 900 degreesC, but it had negative effects on the densification when the control temperature was as low as 850 degreesC. (C) 2003 Elsevier Ltd. All rights reserved.