Abstract: Direct coagulation casting (DCC) is a novel in-situ shape-forming method for ceramic green bodies, especially for fabricating parts with complex shapes. On
the basis of a series of studies, such as surface modification of silicon nitride powder, adjustment of pH in dispersing medium and introduction of efficient dispersant,
silicon nitride suspension with low viscosity and high solid loading was prepared. After optimizing the forming parameters, silicon nitride green body with 60% of
the theoretical density and sufficient strength for demoulding was produced. The green body has homogeneous microstructure and smooth fractured surface. The pore
size distribution of the green body is uniform, narrow and unimodal. At a lower sintered temperature (1750℃), bulk density of the material by pressless
sintered is 98% of the theoretical value. The specimen sintered at 1800℃ for 2h has a homogeneity microstructure, flexure strength of 758.4MPa and a fracture toughness of 6.3 MPa·m^1/2.

Key words: silicon nitride, direct coagulation casting, microstructure, mechanical properties