Effects of heat treatment on mechanical and dielectric properties of 3D Si3N4f/BN/Si3N4 composites by CVI |
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| Affiliation: | 1. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi''an 710072, PR China;2. National Key Laboratory of Thermostructure Composites Materials, Northwestern Polytechnical University, Xi''an 710072, PR China;1. Science and Technology on Thermostructural Composite Materials Laboratory, Northwestern Polytechnical University, Xi''an, 710072, PR China;2. Key Laboratory for Advanced Corrosion and Protection of Aviation Materials, AECC Beijing Institute of Aeronautical Materials, Beijing, 100095, PR China;1. Science and Technology on Advanced Ceramic Fibers and Composites Laboratory, National University of Defense Technology, Changsha 410073, China;2. School of Materials, Sun Yat-sen University, Guangzhou 510275, China;3. Advance Interdisciplinary Technology Research Center, Academy of Military Science, Beijing 100010, China;4. Beijing Institute of Special Electromechanical Technology, Beijing 100012, China |
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| Abstract: | 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. |
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| Keywords: | Composites Mechanical properties Dielectric properties Interfacial diffusion and reaction |
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