FABRICATION AND SOME MECHANICAL-PROPERTIES OF SIC WHISKER-REINFORCED SI3N4 COMPOSITES UTILIZING UNDERWATER-SHOCK PRESSURE

SiC whisker-reinforced Si3N4-based composites without additives were c ompacted by underwater-shock wave. The composites contained 10, 20 and 30 vol% SiC whisker as reinforcements. There were no macrocracks in a ll shock compacted composites. The as-compacted and specimens sintered at various temperatures for 5h were characterized by the measurements of relative density, micro Vickers hardness and fracture toughness. T he relative density of a sintered Si3N4-10 vol% SiC whisker composite was higher than that of sintered Si3N4-20 and 30 vol% SiC whisker comp osites, and reached the theoretical density by sintering at 1973 K. Ha rdness of each composite increased up to 1823 K in proportion to sinte ring temperature, and then saturated above 1823 K. The hardness and fr acture toughness of the Si3N4-30 vol% SiC whisker composite sintered a t 1973 K were about 29 GPa and 5.0 MPa square-root m, respectively. Th e fracture toughness was 25% higher than those of monolithic Si3N4 and other obtained composites sintered at the same temperature. SEM obser vation showed that whisker bridging and deflection were observed in si ntered composites and that the matrix of the Si3N4-30 vol% SiC whisker composite consisted of plate-like and submicron order fine needle-lik e beta-Si3N4 grains.