Processing and Characterization of AlN–SiC Composites Obtained by Spark Plasma Sintering

In this paper, the dependence of the microstructure and properties on Spark Plasma Sintering modes of an AlN-35 β-SiC (wt.%) composite is investigated. It was found that the use of a heating rate of 100 °C/min during the sintering process of the AlN-35 β-SiC (wt.%) composite leads to the formation of a solid solution (AlN)x–(SiC)x−1 at 1900 °C during 5 min, and under a pressure of 50 MPa. It was observed that, at a heating rate of 50 °C/min and a pressure of 25 MPa, yttrium oxide used as a sintering additive impedes the diffusion of SiC into AlN. This impedes the formation of a solid solution (AlN)x–(SiC)x−1 and helps preserve SiC grains, which act as the main absorbing phase in the obtained composites. It is shown that the use of sintering additives and SPS technology allows obtaining samples with a density of 3.26 g/cm3, which coincides with the theoretical value of the composite. The dielectric characteristics and absorbing properties of sintered materials are determined in the frequency bands from 5.6 to 26 GHz. It has been discovered that the reflection, transmission, and absorption coefficients can be regulated depending on the thickness of the sample. In addition, it is shown that composites containing solid solutions and silicon carbide grains in their structures have the best absorbing properties. On the other hand, the material containing only solid solutions is a promising material that can be used as microwave filters.