Reducing chemical vapour infiltration time for ceramic matrix composites

Conventional routes to producing ceramic matrix composites (CMCs) require t he use of high temperatures to sinter the individual ceramic particles of t he matrix together. Sintering temperatures are typically much higher than t he upper temperature limits of the fibres. This paper details preliminary w ork carried out on producing a CMC via chemical vapour infiltration (CVI), a process that involves lower processing temperatures, thus avoiding fibre degradation. The CVI process has been modified and supplemented in an attem pt to reduce the CVI process time and to lower the cost of this typically e xpensive process. To this end microwave-enhanced CVI (MECVI) has been chose n, along with two alternative pre-infiltration steps: electrophoretic infil tration and vacuum bagging. The system under investigation is based on sili con carbide fibres within a silicon carbide matrix (SiCf/SiC). The results demonstrate that both approaches result in an enhanced initial density and a consequent significant reduction in the time required for the MECVI processing step. Dual energy X-ray absorptiometry was used as a nond estructive, density evaluation technique. Initial results indicate that the presence of the SiC powder in the pre-form changes the deposition profile during the MECVI process.