Microstructures and Mechanical Properties of Three-Dimensional Braided Carbon Fiber Reinforced Mullite Composites with Different Sols as Raw Materials

In order to efficiently fabricate dense three-dimensional carbon fiber reinforced mullite matrix composites (3D C/mullite), two kinds of Al2O3-SiO2sols with high solid content were used as raw materials. The ceramic yield and mullitization behavior of the sols and the densification process were investigated. It is indicated that the two sols have proper solid content and ceramic yield and can be completely transformed into mullite at 1573K, which make them be able to prepare composites. 3D C/mullite composites with a porosity of ∼25% were prepared by repeating less than 20 cycles of infiltration-drying-heating of sols, and the microstructures and mechanical properties were examined. The results suggest that the sol with smaller particle size derived composites exhibit well-sintered dense matrix and physically stronger interfacial bonding, which are beneficial to improve load-bearing and load-transferring capacity of matrix. As a result, this composites show much higher mechanical properties. The flexural strength and modulus are 2.4 times and 1.3 times as those of the sol with larger particle size derived composites, respectively.