Fabrication and Some Mechanical Properties of SiC Whisker-Reinforced Si<sub>3</sub>N<sub>4</sub> Composites Utilizing Underwater-Shock Pressure

Abstract

SiC whisker-reinforced Si3N4-based composites without additives were compacted by underwater-shock wave. The composites contained 10, 20 and 30vol% SiC whisker as reinforcements. There were no macrocracks in all 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. The relative density of a sintered Si3N4-10vol% SiC whisker composite was higher than that of sintered Si3N4-20 and 30vol% SiC whisker composites, and reached the theoretical density by sintering at 1973K. Hardness of each composite increased up to 1823K in proportion to sintering temperature, and then saturated above 1823K. The hardness and fracture toughness of the Si3N4-30vol% SiC whisker composite sintered at 1973K were about 29GPa and 5.0MPa√m, respectively. The fracture toughness was 25% higher than those of monolithic Si3N4 and other obtained composites sintered at the same temperature. SEM observation showed that whisker bridging and deflection were observed in sintered composites and that the matrix of the Si3N4-30vol% SiC whisker composite consisted of plate-like and submicron order fine needle-like β-Si3N4 grains.