Abstract
Liquid phase sintering based on the dissolution-precipitation mechanism was applied to densify a 0.8 micrometer SiC powder with alumina (1.2 vol%)-yttria (0.9-3.3 vol%) additives. To uniformly distribute the sintering additives around the SiC particles, a heterocoagulated particle network was formed among negatively charged SiC particles, positively charged 0.2 micrometer alumina and yttrium ions in an aqueous suspension at pH 5. Yttrium ions were electrostatically adsorbed on the negatively charged SiC surfaces. The consolidated green compacts were highly sintered to 97-99% of theoretical density by hot-pressing at 1950°C. The mechanical properties (four-point strength, fracture toughness and Weibull modulus) were highly enhanced when a bimodal particle size system of SiC (0.8 micrometer-30 nanometer SiC) was sintered. The maximum strength of 75 vol% 0.8 micrometer SiC-25 vol% 30 nanometer SiC reached 1.1 GPa at room temperature. The fracture toughness was about 6 MPa·m 1/2 and the Weibull modulus was 5.9. When a small amount of SiC precursor polymer was infiltrated in the green compact, the strength and Weibull modulus were further improved.
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