Abstract: Silicon nitride ceramics were prepared by pressureless sintering , using α-Si3 N4 as raw material, Y2 O3 and MgO as sintering additives .In order to optimize the experiment formulation and process parameters , the effects of forming pressure , pressure-holding time , holding time , sintering temperature , the content and the ratio of sintering additives on the apparent porosity and bending strength of the silicon nitride ceramics were investigated by using the orthogonal experiment .The results show that the content and the ratio of sintering additives mainly affect the apparent porosity of ceramics , but the ratio of sintering additives and sintering temperature mainly affect the bending strength of ceramics .The optimal parameters were as follows:pressure of 16 MPa, pressure-holding time of 120 s, holding time of 2 h, sintering temperature of 1750 ℃, the content of sintering additives of 12wt% and the ratio of sintering additives of 1∶1 .Silicon nitride ceramics sintered after the optimal parameters have the density of 94.53%, apparent porosity of 1.09%and bending strength of 410.73 MPa.

Key words: silicon nitride;orthogonal experiment;porosity;bending strength