Mechanical properties of silicon carbide ceramics densified with rare-earth oxide and alumina additions

Based on the processing strategy of improving the mechanical properties of liquid-phase-sintered materials by tailoring the secondary phase chemistry, four rare-earth oxides (RE(2)O(3)), La(2)O(3), Nd(2)O(3), Y(2)O(3) and Yb(2)O(3), in combination with alumina, were used as sintering aids for a submicron-size P-SiC powder. Doped with 5 vol% RE(2)O(3)+Al(2)O(3), additives, all samples were densified to near theoretical densities by hot pressing at 1800degreesC. The phase compositions, microstructures and mechanical properties of the various SiC ceramics were characterized. It was found that a decrease in the cationic radius of the rare-earth oxides was accompanied by an increase in the hardness and flexural strength and a decrease in the fracture toughness of the SiC ceramics.