Preparation of three-dimensional silica fiber reinforced silicon nitride composites using perhydropolysilazane as precursor

Abstract

Three-dimensional silica fiber reinforced silicon nitride composite materials (3D SiO2f/Si3N4) were prepared through five cycles of vacuum infiltration of perhydropolysilazane (PHPS) and subsequent pyrolysis under ammonia atmosphere. The effects of pyrolysis temperature on densification behavior, mechanical properties and microstructures of the composites were investigated. Preceramic polymer infiltration and pyrolysis process is a fast route for fabrication of dense SiO2f/Si3N4 composites due to the precursor's good wettability with silica fibers and high ceramic yield. With the increase of pyrolysis temperature from 600 to 800 °C, the density of SiO2f/Si3N4 composites increases from 1.80 to 1.91 g/cm3, while the flexural strength decreases from 45.4 to 33.5 MPa, and the elastic modulus decreases from about 23.8 to 16.3 GPa. The higher temperatures generate strong adhesion of fiber/matrix interface and hence lead to brittle, low-strength composites. It is the different interfacial microstructures that result in different mechanical properties.