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 m ixing appropriate powders and hot pressing above the glass transition temperature. Some of the specimens were subjected to postsintering cry stallization treatments. The resultant sintered microstructure was tex tured, and within it the SiC platelets tended to be oriented with thei r basal planes perpendicular to the hot-pressing direction. The bendin g strength of the hot-pressed specimens was constant, while the fractu re toughness increased with the SiC content. Crystallization heat trea tment in argon for 30 min at 1200 degrees C caused a significant decre ase in the bending strength, but improved the fracture toughness. Frac tography has confirmed the crack deflection to be a dominant mechanism in the crystallized specimens, which contributes to the improvement i n the fracture toughness. The overall changes in the mechanical proper ties are discussed with respect to the change in the residual stresses and oxidation characteristics of the SiC platelets.