Effect of SNNWS content on the microstructure and properties of SNNWS/Si-C-N ceramic composites via PIP

Abstract

Si-C-N ceramic composites containing well distributed silicon nitride nanowires (SNNWs) were fabricated by die-pressing and precursor infiltration and pyrolysis process at a low temperature. The structure, composition, mechanical and thermophysical properties of the composites were investigated. The results show that the composites consisted of amorphous SiCN, α-Si3N4 and α-cristobaslite. The composites with different contents of SNNWs possessed a density of 2.02–2.07gcm−3 and open porosity of 7.9–9.9%. SNNWs can effectively restrain the contraction of matrix with a decrease by 25% in linear shrinkage. The composites with 3wt% SNNWs owned the highest flexural strength (83.7MPa) and elastic modulus (54.0GPa) at room temperature, which increase by 13.2% and 62.3% respectively, compared with pure SiCN ceramics. The SNNWs displayed good reinforcement function at high temperature due to the fact that the composites with 7wt% SNNWs had a 96.8% retention rate of bending strength at 1200°C. The composites had relatively low coefficient of thermal expansion and thermal diffusivity which were less than 2.2 × 10−6K−1 and 0.62mm2s−1, respectively.