Preparation of Al2O3/SiC nanocomposites with in-situ formed SiC

Powder mixtures containing Al2O3, SiO2 and carbon black were calcined at 1625 degrees C to form nanoscaled SiC within Al2O3 by means of the carbothermal reduction of SiO2. The prepared powders contained 5 and 10 Vol. % SiC. These powders were densified by hot pressing, and composite ceramics with densities up to 99 % obtained. Microstructural analyses of the hot-pressed composites showed a homogeneous distribution of SiC particles with a particle size mainly under 100 nm. The fracture mode was intragranular. The fracture toughness determined by the ICL method using the Niihara approach for Palmqvist cracks was in the range of 5 MPa.m(0.5). The fracture strength determined in a four-point bending test was around 540 MPa for the hot-pressed samples and around 630 MPa for the hot-pressed and postannealed samples.