Sintering and Vickers Hardness on Composite of Si3N4-SiC System

The Si3N4-SiC composite (0 to 0.25wt fraction of SiC) system was investigated to understand the effect of addition of one metal oxide (e.g. MgO, Al2O3, Y2O3 or CeO2) and two metal oxides (e.g. Y2O3-Al2O3, CeO2-Al2O3 etc.) on the sintering and Vickers hardness. The composites were hot-pressed at 1700°C under 400kg·mm-2 or pressureless-sintered at 1700° and 1800°C. The results are as follows: The relative density of the composite decreased with the increasing of SiC content. The hot-pressed composites with 5wt% Y2O3+10wt% Al2O3 and 5wt% CeO2+10wt% Al2O3 had 96 to 98% relative density and 1800 to 2000kg·mm-2 Vickers hardness (at 5kg load), and pressureless-sintered composites with 5wt% Y2O3+10wt% Al2O3 fired at 1700°C far 4h had 87% relative density and 1200kg·mm-2 Vickers hardness.