MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF SIC PLATELET CORDIERITE CLASS CERAMIC COMPOSITES

Cordierite glass-ceramics reinforced with different volume fractions (0, 10, 20, and 30%) of SiC platelets were fabricated by mechanically mixing appropriate powders and hot pressing above the glass transition temperature. Some of the specimens were subjected to postsintering crystallization treatments. The resultant sintered microstructure was textured, and within it the SiC platelets tended to be oriented with their basal planes perpendicular to the hot-pressing direction. The bending strength of the hot-pressed specimens was constant, while the fracture toughness increased with the SiC content. Crystallization heat treatment in argon for 30 min at 1200 degrees C caused a significant decrease in the bending strength, but improved the fracture toughness. Fractography has confirmed the crack deflection to be a dominant mechanism in the crystallized specimens, which contributes to the improvement in the fracture toughness. The overall changes in the mechanical properties are discussed with respect to the change in the residual stresses and oxidation characteristics of the SiC platelets.