Effects of heat treatment on mechanical and dielectric properties of 3D Si3N4f/BN/Si3N4 composites by CVI

• Published in: Journal of the European Ceramic Society 2020-12, Vol.40 (15), p.5305-5315
• Main Authors: Zhou, Jie, Cheng, Laifei, Ye, Fang, Zhang, Litong, Liu, Yongsheng, Cui, Xuefeng, Fu, Zhiqiang
• Format: Article
• Language: English
• Subjects: Composites; Dielectric properties; Interfacial diffusion and reaction; Mechanical properties; Si3N4f/BN/Si3N4
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2020.06.018

In this study, three-dimensional silicon nitride fiber-reinforced silicon nitride matrix (3D Si3N4f/BN/Si3N4) composites with a boron nitride (BN) interphase were fabricated through chemical vapor infiltration. Through comparing the changes of microstructure, thermal residual stress, interface bonding state, and interface microstructure evolution of composites before and after heat treatment, the evolution of mechanical and dielectric properties of Si3N4f/BN/Si3N4 composites was analyzed. Flexural strength and fracture toughness of composites acquired the maximum values of 96 ± 5 MPa and 3.8 ± 0.1 MPa·m1/2, respectively, after heat treatment at 800 °C; however, these values were maintained at 83 ± 6 MPa and 3.1 ± 0.2 MPa·m1/2 after heat treatment at 1200 °C, respectively. The relatively low mechanical properties are mainly attributed to the strong interface bonding caused by interfacial diffusion of oxygen and subsequent interfacial reaction and generation of turbostratic BN interphase with relatively high fracture energy. Moreover, the Si3N4f/BN/Si3N4 composites also displayed moderate dielectric constant and dielectric loss fluctuating irregularly around 5.0 and 0.04 before and after heat treatment, respectively. They were mainly determined based on the intrinsic properties of materials system and complex microstructure of composites.