颗粒级配对Si₃N₄w/Si₃N₄复合材料弯曲强度与介电性能的影响

In order to obtain a nitride ceramic material with good flexural and dielectric properties, using silicon nitride whiskers (Si₃N₄w) as raw material, three kinds of Si₃N₄w spherical particle powders with different particle size distributions were prepared by spray drying process at first in this work, and the effect of the rotating speed of the atomizing disc on the particle size distribution of Si₃N₄w spherical particles was studied. Then, using the Si₃N₄w spherical particles obtained by spray drying as raw materials, three kinds of Si₃N₄w preforms with different particle gradations were prepared by dry pressing method, and the pore size distribution of the particle gradation Si₃N₄w preforms was studied. Si₃N₄ matrices were further prepared in three kinds of particle gradation Si₃N₄w preforms by chemical vapor infiltration (CVI) and precursor impregnation and pyrolysis (PIP) methods, and the phase and microstructure evolution of Si₃N_4w/Si₃N₄ composites during the preparation process were investigated. Finally, the effect of particle gradation on the microstructure, density, flexural and dielectric property of Si₃N_4w/Si₃N₄ composites was studied. The results show that the three kinds of particle gradation Si₃N₄w preforms all have bimodal pore structure characteristics, in which the pore sizes of small pores are all about 0.7 μm, and the pore sizes of large pores are 45.2, 30.1 μm and 21.3 μm, respectively. Among the as-prepared three types of Si₃N_4w/Si₃N₄ composites with particle gradation, the flexural strength of the S13 composites reaches 81.59 MPa since it has the best particle gradation effect. In addition, the dielectric constant and dielectric loss of this sample are 5.08 and 0.018, respectively. Good flexural strength and dielectric properties indicate that the as-prepared Si₃N_4w/Si₃N₄ composites are expected to be used in the field of missile radomes.