Microstructure and properties of particle reinforced silicon carbide and silicon nitride ceramic matrix composites prepared by chemical vapor infiltration

Introduction: Particle reinforced silicon carbide and silicon nitride ceramic matrix composites were fabricated using designed particle agglomeration and chemical vapor infiltration (CVI) technique. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) were employed to observe the microstructures of the preforms and as-infiltrated composites. In the preform, the inter-agglomeration and intra-agglomeration pores had an approximate size of 500-800 μm and 5-10 μm, respectively. After infiltrated, a large amount of silicon carbide and silicon nitride matrix were infiltrated in the preform, the sizes of inter-agglomeration and intra-agglomeration pores were 200-400 μm and 2-4 μm, respectively. The SiC and Si₃N₄ whiskers were observed in the residual intra-agglomeration pores. The flexural strength of SiC_(p)/SiC composites changed with first-step pressure and second-step pressure. The maximum of the strength was 284 MPa, and the ratio of the retained strength was 95.4% at 1600 °C. The fracture toughness of SiC_(p)/SiC composites was around 7 Mpa m^1/2. The Si₃N_4(p)/Si₃N₄ composite attained an acceptable strength, 113.4 MPa and low dielectric constant, about 4.2-4.3.