Effect of Sintering Pressure on Mechanical Properties of BN-Si<sub>3</sub>N<sub>4</sub> Ceramic Composites Prepared by Spark Plasma Sintering

BN-Si 3 N 4 composite ceramic wave-transparent materials with excellent mechanical properties were prepared by spark plasma sintering (SPS) using h-BN and α-Si 3 N 4 powders as raw materials, Al 2 O 3 and Y 2 O 3 as sintering aids. The influence of sintering pressure on density and mechanical properties of BN-Si 3 N 4 composite ceramics were studied. The phases were observed by X-ray diffraction (XRD), and the microstructures were identified by scanning electron microscopy (SEM). The results showed that with the sintering pressure increases, the relative density, bending strength and fracture toughness of the composite ceramics were significantly increased, and the porosity decreased rapidly. The effects of pressure on the properties of the composite ceramics was not significant at >40MPa, so 40MPa is optimal for the composite ceramics to gain good overall performance, i.e. the relative density was 89.1%, the porosity was 2.3%, the bending strength reached 215.4 MPa, and the fracture toughness was 3.1/MPa·m 1/2 .