Mechanical Properties of Reaction-bonded Si_3N_4/SiC Composite Ceramics

With Y2O3:Al2O3(A 2:3; B 3:1 total amount 15wt%) as sintering additives and SiC as the second phase,high flexural strength Si3N4/SiC composite ceramics were prepared via nitridation of Si powder. The phase composition,relative density,microstructure as well as mechanical properties were investigated. The experimental results showed that the α→β-Si3N4 phase transformation could be completed at 1700℃ for 2 h with sintering additives A or B. With the sintering additive A and 5wt% SiC addition,the maximum relative density of 94.8% and maximum flexural strength of 521.8 MPa were obtained for the Si3N4/SiC composite ceramics. As compared with the specimen without SiC addition which flexural strength was 338.7 MPa,flexural strength of the above mentioned Si3N4/SiC composite ceramics was improved by 54.1%. SiC powder can effectively improve the mechanical properties of the specimen and the fracture of Si3N4/SiC composite ceramics followed the typical intergranular fractural mode.