Effect of C/C porous preform on the microstructure and flexural strength of C/C-SiC composites

Carbon fiber reinforced silicon carbide matrix (C/C-SiC) composites were prepared by liquid silicon infiltration (LSI) process, using four kinds of quasi-three dimensional C/C preforms with the same fiber volume faction (32%) but different pyrocarbon content (from -20% to -50%, in volume) filled by chemical vapor infiltration. The microstructure and flexural strength of C/C-SiC composites have been investigated. XRD analysis results show the composites are composed of three phases of β-SiC, C and Si. With the increase of the pyrocarbon content in the C/C preforms, the content of formed silicon carbide in the C/C-SiC composites decreases but the residual pyrocarbon increases. Flexural test was performed to assess the role of the matrix in the C/C-SiC compo- sites. The results demonstrate that the flexural strength of the composite increases gradually as the increase of the content of residual pyrocarbon. The bending strength of the C/C-SiC composite produced of the C/C preform with pyrocarbon content of -42% is the highest of 320 MPa.