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 pr essing. The hot-pressed materials were subsequently annealed to enhanc e grain growth, The diameters and aspect ratios of grains in the hot-p ressed and annealed materials were measured on polished and etched sur faces. The bimodal grain size distribution in annealed materials was o btained at 1850 degrees C without appreciable phase transformation. Th e average diameter and average aspect ratio increased with annealing t ime. 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 b y annealing at 1850 degrees C for 12 h. Higher fracture toughness of a nnealed materials is due to bridging by elongated grains as evidenced by R-curve-like behavior.