In this case the matrix is formed by the CVI of SiC, a process which takes from 300-600 hours. Properly fabricated C-SiC can operate up to 1650 C in an oxidizing environment for a limited period of time. Its life is governed by cracking in the matrix which permits the oxidizing gas to attack the carbon fibers. This cracking is caused by the stresses developed due to the coefficient of expansion mismatch between the carbon fibers and the SiC matrix, which also results in through the wall porosity in the composite. To date SiC-SiC composites are limited to operating temperatures of about 1200 C because of degradation of the SiC fibers.
Typical fabrication proceeds as shown below.
A mandrel whose outside surface replicates the inner surface of the desired structure is first fabricated. The outer surface is then processed with a sufficient thickness of C-C to meet the structural requirements and the mandrel is removed.