Effects of SiO2 and rare-earth oxide additions on densification and mechanical properties of silicon carbide ceramics

Effects of co-addition of SiO2 and rare earth oxide (REO) such as Eu2O3, Sm2O3, Gd2O3, Y2O3 on densification and mechanical properties of SiC ceramics were studied. Sintering was performed using hot-pressing method at 1950 degreesC with applied pressure of 40MPa for wide ranges of additive composition. Relative densities of the specimens sintered with SiO2-REO were improved compared with the specimen sintered with only REO. Grain growth of SiC was suppressed and higher bending strength more than 800 MPa was achieved via liquid phase sintering containing large amount of SiO2. Secondary phases were mostly amorphous in the case of large amount of SiO2, and rare earth silicates in the case of small amount of SiO2 addition. It was suggested that addition of large amount of SiO2 was effective to improve density and bending strength of SiC ceramics.