Fabrication and mechanical properties of SiC platelet reinforced mullite matrix composites

Hot-pressing of mullite and SiC-mullite matrix composites was performed at temperatures and pressures between 1500 and 1650 degrees C and 5 and 15 MPa , respectively. Composites were produced using different precursors; sol-ge l derived mullite and kaolinite/alpha-alumina. The precursor did not strong ly affect the optimum density achieved, reaching 97.5% of theoretical for a 20 vol% SiC addition in both cases. The SiC platelet addition impaired den sification kinetics in all composites compared to mullite monoliths. Fractu re toughness, measured by the indentation strength in bending technique, wa s marginally higher for the sol-gel precursor material in both monolith and composite. Fracture toughness increased with SiC content for both material s. For example, for the sol-gel precursor material it increased from 2.9 +/ - 0.1 MPa m(1/2) for the monolith to 3.9 +/- 0.1 MPa m(1/2) for the 20 vol% SiC composite. Similarly, hardness increased with SiC addition for both ma terials, but the hardness of the sol-gel material was greater than that of the kaolinite + alpha-alumina material for all compositions. The relationsh ip between microstructure and mechanical proper ties is discussed. (C) 1999 Published by Elsevier Science Limited. All rights reserved.