Yongsheng Liu, Litong Zhang, Laifei Cheng, Yongdong Xu, Yi Liu
Online: Nov 5 2008 3:10PM
Silicon nitride particle-reinforced silicon nitride matrix composites were fabricated by chemical vapor infiltration (CVI). The particle preforms with a bimodal pore size distribution were favorable for the subsequent CVI process, which included intraagglomerate pores (0.1-4 μm) and interagglomerate pores (20-300 μm). X-ray fluorescence results showed that the main elements of the composites are Si, N, and O. The composite is composed of α-Si3N4, amorphous Si3N4, amorphous SiO2, and a small amount of β-Si3N4 and free silicon. The α-Si3N4 transformed into β-Si3N4 after heat treatment at 1600°C for 2 h. The flexural strength, dielectric constant, and dielectric loss of the Si3N4(p)/Si3N4 composites increased with increasing infiltration time; however, the pore ratios decreased with increasing infiltration time. The maximum value of the flexural strength was 114.07 MPa. The dielectric constant and dielectric loss of the composites were 4.47 and 4.25 × 10-3, respectively. The present Si3N4(p)/Si3N4 composite is a good candidate for high-temperature radomes.