Developing and preparing interfacial coatings for high tensile strength silicon nitride fiber reinforced silica matrix composites

A three-dimensional silicon nitride fiber fabric with Pyrolytic carbon (PyC) interlayer reinforced silica matrix composites (Si₃N_4f/PyC/SiO₂) were prepared by sol-gel method, and the mechanical properties of the composites were investigated. The tensile strength of Si₃N_4f/PyC/SiO₂ composites at room temperature exceeded 73.8 MPa, and the tensile strengths at 1200 °C and 1400 °C were 60.9 MPa and 58.2 MPa, respectively. Compared with Si₃N_4f/SiO₂ composites without PyC coating, the strength of Si₃N_4f/PyC/SiO₂ composites improved significantly, particularly at high temperature. The experimental results show that PyC interlayer could protect silicon nitride fibers from high temperature interfacial reaction between fibers and matrix. Meanwhile, considerable fiber pull-out was observed throughout the fracture surface of Si₃N_4f/PyC/SiO₂ composites indicating that the interface bonding was weak, which resulted in the high mechanical strength of Si₃N_4f/PyC/SiO₂ composites.