Pressure swing CVI/CVD

Method of chemical vapor infiltration of a deposable carbon material into a porous carbon fiber preform in order to densify the carbon fiber preform. The method includes the steps of: situating the porous carbon fiber preform in the reaction zone; providing a linear flow of an reactant gas comprising deposable carbon material in the reaction zone at an initial reaction pressure of at most 50 torr to produce deposition of the deposable carbon material into the preform; and adjusting the pressure of thc gas to reaction pressures lower than said initial reaction pressure while deposable carbon material continues to be deposited into the porous carbon fiber preform. This method enables attainment of a target increased density in a carbon fiber preform much more quickly than known processes. A programmed pressure swing throughout the CVI/CVD run may be set in order to provide a linear increase in density. Alternatively, step changes in pressure during the course of the densification process may be made to enhance the rate of densification. This method reduces the number of cycles and the required intermediate machining steps necessary to densify preforms.