Properties of hot-pressed of SiC/Si3N4 nanocomposites

SiC/Si3N4 nanocomposites were prepared with carbon black and α-Si3N4 powders by hot-pressed method. The microstructure, phase composition, dielectric and mechanical properties of the nanocomposites were investigated. The relative densities of SiC/Si3N4 nanocomposites decreased from 99 to 86% when the carbon black content increased from 0 to 10 wt%. The X-ray diffraction (XRD) analysis shows that there are SiC crystals formed during the sintering process in the samples with carbon black. The main crystalline phase in the pure Si3N4 ceramic is β-Si3N4. The scanning electrical microscope (SEM) photographs reveal that the Si3N4 grains in Si3N4 ceramic are big and elongated. But the transformation of α-Si3N4 to β-Si3N4 is impeded in the samples with carbon black. More α-Si3N4 were retained in the nanocomposites with the increase of the carbon black content. The Si3N4 grains in samples with carbon black are small and particulate. The reason is that the incorporation of carbon black increases the viscosity of sintering liquid and prevents the transformation of α-Si3N4 to β-Si3N4 and the growth of Si3N4 grain. The strength of the nanocomposites is degraded due to the addition of the carbon black. The real and imaginary parts of the permittivity and dielectric loss of the SiC/Si3N4 nanocomposites all increase with the increase of carbon black content.