The effect of sol/particle reaction on properties of two-dimensional ceramic matrix composites

Two-dimensional (2-D) ceramic matrix composites composed of carbon fiber fa bric and alumina/mullite matrices have been fabricated by sol-gel processin g using silica sol and alumina particles. The pressure infiltration method can effectively infiltrate the mixture of sol and particles into the fabric . and multiple infiltration is followed to increase the green density. Afte r five infiltration cycles, the composite green density increased from 75% to approximately 81.7%, and to around 88% by hot pressing. Using the silica gel/alumina particles route, the mullite matrix was verified to exist by X -ray diffraction (XRD). and increased the shear strength of the composite b y enhancing interfacial bonding. The effect of nitric acid treatment of the carbon fabric on the mechanical properties of the composites is evaluated. The average shear strength and work of fracture of composites with a fiber volume fraction of 24.7% were, respectively, 60.7 MPa and 213.3 kJ/m(3) wi th treated fibers, and 40.4 MPa and 116.0 kJ/m(3) with untreated fibers. Lo cal kink is the major failure mode for composites with treated fibers, whil e delamination is the major failure mode for composites with untreated fibe rs. (C) 2001 Elsevier Science B.V. All rights reserved.