Effect of nano-SiO₂ on mechanical properties of SiC_f/SiC composites fabricated via precursor infiltration pyrolysis process

The 2.5-dimensional silicon carbide fiber reinforced silicon carbide (2.5D-SiC_f/SiC) composites were fabricated via a precursor infiltration pyrolysis (PIP) process with a nano-sized silica powder as a filler. The influence of nano-SiO₂ content in the precursor solution on the mechanical properties of the as-received SiC_f/SiC composites was investigated. The results show that the introduction of nano-SiO₂ can restrain the shrinkage upon the pyrolysis and densify the composites efficiently. However, the excessive amount of SiO₂ could cause a high viscosity of impregnation solution, resulting in the lower infiltration efficiency. The content of nano-sized SiO₂ had an influence on the mechanical properties of the composites. The flexural strength and fracture toughness of the composites with the nano-sized SiO₂ filler both were better than those without the nano-sized SiO₂ filler. The flexural strength of the composites firstly increased and then decreased with the increase of nano-sized SiO₂ content. The superior mechanical properties could be obtained, i.e., the flexural strength could reach 211.1 MPa, when the nano-sized SiO₂ content was 6%.