Abstract
Wave-transparent ceramic composites with excellent comprehensive performances are of particular significance for the development of space vehicles. In this study, Si3N4w was prepared by the gel-casting process and then combined with chemical vapor infiltration (CVI)-obtained Si3N4 to yield Si3N4w/Si3N4 composites with five Si3N4w volume fractions. The influence of the Si3N4w volume fraction on the microstructures, mechanical properties, and dielectric characteristics of the Si3N4w/Si3N4 composites were all studied. The results showed that Si3N4w/Si3N4 composites possess A sandwich structures. Higher Si3N4w volume fractions led to less incorporated amounts of the Si3N4 matrix at the same depth. The 25 vol% Si3N4w/Si3N4 composites integrated relatively higher Si3N4w 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 Si3N4w/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 Si3N4w/Si3N4 composites.
Highlights
High-temperature wave-transparent materials are used in spacecraft radomes and antenna windows, which require good mechanical and dielectric properties, as well as high-temperature resistance
The results suggested that the 25 vol% Si3N4w/Si3N4 possessed the highest comprehensive performances
The smooth and flat surface revealed the advantages of the gel-casting in terms of near net-size forming
Summary
High-temperature wave-transparent materials are used in spacecraft radomes and antenna windows, which require good mechanical and dielectric properties, as well as high-temperature resistance. At a fiber volume fraction of 25%, the maximum flexural strengths of the composites reached 48.86 MPa. Using the hot-pressing sintering method, Xu et al (1994) prepared SiCf/Si3N4 with a fiber volume fraction of 14, 29, and 55 vol%. Using the hot-pressing sintering method, Xu et al (1994) prepared SiCf/Si3N4 with a fiber volume fraction of 14, 29, and 55 vol% Their data suggested that the flexural strength of the composites first increased with the fiber volume fraction and decreased. The effects of whisker volume fractions on the microstructures, mechanical properties, and dielectric characteristics of the Si3N4w/Si3N4 composites were all studied. The influences of volume fractions of Si3N4w on the microstructures, mechanical properties, and dielectric characteristics of Si3N4w/ Si3N4 were all studied. The experiments were performed at a standard dielectric sample size of 22.86 mm × 10.16 mm × h mm and a testing frequency band of 8.2–12.4 GHz
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