An 800 nm-SiC powder (75 vol%) was mixed with a 30 nm-SiC powder (25 vol%) in a 0.3 mol/l Y(NO3)3 solution containing an Al2O3 powder of median size 200 nm at pH 5 to distribute homogeneously the sintering additives (Al2O3+Y3+ ion) around the SiC particles. Polyacrylic acid of 1.0 mg/m2-SiC surface was added as a dispersant. This suspension was consolidated by casting in a gypsum mold. The green compacts of 43% theoretical density were hot-pressed to a relative density 98.1 ± 2.1% at 1950 oC in an Ar atmosphere. The strength of the dense SiC was in the range from 560 to 1080MPa (average strength 810MPa, Weibull modulus 5.9). The as-hot-pressed SiC was heat-treated in air for 24 h at 1100o and 1300 oC. The heat-treatment at 1100 oC improved the strength in the low fracture probability range (< 40%) and narrowed the strength range (700-1250MPa, average strength 820 MPa). On the other hand, the heat-treatment at 1300 oC shifted greatly the strengths in all the fracture probability range to higher values (750-1180 MPa, average strength 960MPa). The Weibull modulus was also increased to 8.3. The above results may be related to the decrease of size and shape factor of fracture origins near the SiC surfaces by the formation of SiO2. A compressive stress may be also produced on the surface region of the dense SiC which contributes to the increased strength.

Keywords: Silicon carbide, Sintering additives, Hot-pressing, Oxidation, Fracture strength, Weibull modulus.