Mechanical Properties and Microstructural Characteristics of Carbon Fiber Reinforced Silicon Carbide Matrix Composites by Chemical Vapor Infiltration

Three dimensional carbon/silicon carbide composites were prepared by chemical vapor infiltration, and the microstructure and the mechanical properties were investigated. For the composites (C/SiC) with no pyrolytic carbon interfacial layer, the mechanical properties (flexural strength, flexural elastic modules, shear strength, and fracture toughness) increase with the density of the composites. High density (ρ=2.1g·cm^-3) C/SiC composites exhibit high fracture toughness (16.5 MPa·m^1/2) but brittle fracture behavior because of strong bonding between fiber/matrix. Low density composites show non-catastrophic failure mode with long bundle pull-out. The composites (C/PyC/SiC) with pyrolytic carbon interfacial layer exhibit good mechanical properties and a typical failure behavior. Microstructural observations reveal that the tortuosity and bottleneck effect of the pores are two key issues which hinder the densification of composites.