The Influence of Si₃N_4w Volume Fraction on the Microstructure and Properties of Si₃N_4w/Si₃N₄ Composites via CVI Technique

Wave-transparent ceramic composites with excellent comprehensive performances are of particular significance for the development of space vehicles. In this study, Si₃N_4w was prepared by the gel-casting process and then combined with chemical vapor infiltration (CVI)-obtained Si₃N₄ to yield Si₃N_4w/Si₃N₄ composites with five Si₃N_4w volume fractions. The influence of the Si₃N_4w volume fraction on the microstructures, mechanical properties, and dielectric characteristics of the Si₃N_4w/Si₃N₄ composites were all studied. The results showed that Si₃N_4w/Si₃N₄ composites possess A sandwich structures. Higher Si₃N_4w volume fractions led to less incorporated amounts of the Si₃N₄ matrix at the same depth. The 25 vol% Si₃N_4w/Si₃N₄ composites integrated relatively higher Si₃N_4w volume fraction and load transfer ability of the matrix, leading to better flexural strengths reaching up to 41.37 MPa. The dielectric constants of the five prepared Si₃N_4w/Si₃N₄ composites ranged from 2.25 to 4.0. The dielectric losses were all lower than 0.005, demonstrating the good dielectric properties of the Si₃N_4w/Si₃N₄ composites.