GRAIN-GROWTH AND FRACTURE-TOUGHNESS OF FINE-GRAINED SILICON-CARBIDE CERAMICS

Fine-grained silicon carbide ceramics with an average grain size of 0.11 mu m were liquid-phase sintered from fine beta-SiC powder by hot pressing. The hot-pressed materials were subsequently annealed to enhance grain growth, The diameters and aspect ratios of grains in the hot-pressed and annealed materials were measured on polished and etched surfaces. The bimodal grain size distribution in annealed materials was obtained at 1850 degrees C without appreciable phase transformation. The average diameter and average aspect ratio increased with annealing time. The fracture toughness of a fine-grained silicon carbide ceramic determined by the Vickers indentation method was 1.9 MPa . m(1/2). The fracture toughness increased to 6.1 MPa . m(1/2) after grain growth by annealing at 1850 degrees C for 12 h. Higher fracture toughness of annealed materials is due to bridging by elongated grains as evidenced by R-curve-like behavior.