Thermal Shock Resistance of Mullite-Based SiC-Whisker Composites

摘要

The influence of the addition of silicon carbide (SiC) whiskers and zirconia on the material properties and constants of pure mullite was examined. SiC whisker weight percentages of 0, 10, 20, and 30 were examined, and a zirconia content of 36.1 wt.% was studied. A theoretical approach similar to Hasselman's high-E, low-E theory was used to determine the theoretical values of the material properties which were then compared to experimental results. Using experimental and theoretical values for Young's modulus of elasticity, bend strength, mean coefficient of thermal expansion, thermal diffusivity, and Poisson's ratio, the thermal stress resistance parameters were calculated, and compared to experimental results for critical quench temperatures. Microstructures were characterized by x-ray diffraction (XRD) analysis, chemical analysis, density determinations, light microscopy (LM), and scanning electron microscopy (SEM). The mullite was alumina-rich with particles of silica present. Whisker composites contained 2H, 4H, and 15R polytypes of SiC and impurities from the whisker. Mullite-zirconia microstructures contained partially-stabilized zirconia with monoclinic:tetragonal ratios of 90%. Increasing SiC whisker content decreased the Poisson's ratio and mean coefficient of thermal expansion of the specimen and increased the elastic modulus, bend strength, and thermal diffusivity of the composites.