Pulsed chemical vapour infiltration of SiC to three-dimensional carbon fibre 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°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 10⁵ when no filler was present. However, the weight increase slowed down above 8×10⁴ 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 10⁵ pulses, respectively. In order to improve the strength, a denser filling of SiC powder is necessary.