Fabrication and some mechanical properties of SiC whisker-reinforced Si₃N₄ composites utilizing underwater-shock pressure

SiC whisker-reinforced Si₃N₄-based composites without additives were compacted by underwater-shock wave. The composites contained 10, 20 and 30 vol%SiC whisker as reinforcements. There were no macrocracks in all shock compacted composites. The as-compacted and specimens sintered at various temperatures for 5 h were characterized by the measurements of relative density, micro Vickers hardness and fracture toughness. The relative density of sintered Si₃N₄-10 vol%SiC whisker composite was higher than that of sintered Si₃N₄-20 and 30 vol%SiC whisker composites, and reached the theoretical density by sintering at 1973 K. Hardness of each composite increased up to 1823 K in proportion to sintering temperature, and then saturated above 1823 K. The hardness and fracture toughness of the Si₃N₄-30 vol%SiC whisker composite sintered at 1973 K were about 29 GPa and 5.0 MPa√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 Si₃N₄-30 vol%SiC whisker composite consists of plate-like and submicron order fine needle-like β-Si₃N₄ grains.