Effect of Sintering Pressure on Mechanical Properties of Silicon Nitride Ceramics

In pressure sintering of silicon nitride ceramics, nitrogen pressure has a great impact on its properties besides sintering heating system. In order to prepare silicon nitride ceramics with desired properties, this paper was aimed to elucidate the effect of nitrogen pressure on mechanical properties of silicon nitride ceramics. When the nitrogen pressure is about 4 MPa, comprehensive properties of the silicon nitride ceramic materials are the highest, while the α-β phase transition is nearly completed. The aspect ratio of β-Si₃N₄ grains is about 5.5 and the relative density is about 97.9%. The bending strength is about (671.83±30.00) MPa, the hardness is about (1670.25±50.00) HV and the fracture toughness is about (7.83±0.3.00) MPa·m^1/2. According to the microstructure of corroded surface and indentation cracks, it is found that appropriate nitrogen pressure resulted in crack deflection, bifurcation and other toughening mechanisms on the expansion path, consuming the crack diffusion energy and thus improving fracture toughness of the silicon nitride ceramics. The results could be used as a reference for the toughening of silicon nitride ceramic materials.