Effect of Different Sintering Additives on the Microstructure, Phase Compositions and Mechanical Properties of Si3N4/SiC Ceramics

Y 2 O 3 and CeO 2 were chosen as additives to investigate the effect of different additives on the microstructure, composition of phases, and mechanical properties of Si 3 N 4 /SiC ceramics using pressureless sintering.Si 3 N 4 /SiC ceramic without additives had a high density, while after adding Y 2 O 3 and CeO 2 , the density and flexural strength of Si 3 N 4 /SiC ceramics were significantly decreased due to the increase in porosity.The main phase compositions of the samples were β-Si 3 N 4 and SiC.Moreover, the liquid phases Y-Si-O-N and Ce-Si-O-N were observed after adding Y 2 O 3 and CeO 2 respectively.It also indicated that for Si 3 N 4 /SiC composite ceramics, the high aspect ratio β-Si 3 N 4 overlapped with each other and closely bonded with the glass phase could improve flexure strength effectively.Besides, the SiC crystal grains mainly existed in the grain boundary, which could inhibit the secondary recrystallization to avoid the decrease of flexural strength caused by the overgrowth of β-Si 3 N 4 grains.