PULSED CHEMICAL VAPOR INFILTRATION OF SIC TO 3-DIMENSIONAL CARBON-FIBER PREFORMS

Three-dimensional carbon fibre preforms were infiltrated with silicon carbide from a gas system of CH3SiCl3-H2 using a process of pressure pulsed chemical vapour infiltration. To infiltrate to a deep level, the temperature had to be lowered to 870-900-degrees-C, and the hold time per pulse below 1.0 s. Three-dimensional carbon fibre preforms partly filled with SiC fine powder were compared with those without filler. The weight of the preforms increased linearly with increasing number of pulses up to 10(5) when no filler was present. However, the weight increase slowed down above 8 x 10(4) pulses when the filler was used. Preforms with and without SiC filler showed three-point flexural strengths of 160 and 80 MPa after CVI of 10(5) pulses, respectively. In order to improve the strength, a denser filling of SiC powder is necessary.