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

Introduction le 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 m1/2. The Si3N4(p)/Si3N4 composite attained an acceptable strength, 113.4 MPa and low dielectric constant, about 4.2–4.3.