Effect of Sintering Aids on Thermal Conductivity and Mechanical Properties of Silicon Nitride Ceramics

Abstract: β-phase high thermal conductivity silicon nitride ceramics were prepared by sintering at 1900 ℃ for 2 h using silicon nitride (α-phase≥95%, particle size 0.5 μm) as a raw material, and MgO–Y2O3 as a composite sintering aid. The effects of sintering aid content and ratio on the densification process, thermal conductivity, mechanical properties and microstructure of silicon nitride ceramics were discussed. The results show that when the addition amount of sintering aid is 5% MgO+4% Y2O3, the thermal conductivity, bending strength, fracture toughness of the sample sintered in air at 1890℃ for 2 h can reach 85.96W·m–1·K–1, 873 MPa and 8.39 MPa·m1/2, respectively. In the sintering process, Y2O3 reacts with Si3N4 to form a compound fixed at the grain boundary, which plays a role in purifying the silicon nitride lattice and improves the thermal conductivity of the sintered sample. Excessive MgO and Y2O3 will form compounds during the sintering process and remain at the grain boundary, which will reduce the mechanical properties and thermal conductivity of the material.

Keywords: silicon nitride; gas press sintering; thermal conductivity; mechanical properties; microstructure 

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