Structural evolution and properties of SiC/SiBCN composites at elevated temperatures

Abstract

The SiC/SiBCN composites were prepared via polymer infiltration and pyrolysis (PIP) technique. The structural composition and property evolution behavior of the composites under inert high-temperature environment were investigated to reveal the failure mechanism of the composites. With the increase of the heat treatment temperature from 1500 °C to 1600 °C, the composite properties underwent a sharp decline. Among them, the weight loss rate gradually increased from 3% to 9% and the density decreased from 2.4 g/cm3 to 2.3 g/cm3. Especially, the room temperature flexural strength decreased from 267 ± 7 MPa to 179 ± 3 MPa and the strength retention were 46%. The degradation of SiC fiber properties is the main factor for the decrease in flexural strength of the composites at below 1500 °C. When heat treatment temperature above 1600 °C, the mechanical properties of SiC fiber dramatically decline, and the SiBCN ceramic matrix initially precipitated Si3N4 crystalline phase leading to a carbothermal reduction reaction. Hence, the mechanical properties of the composite at T > 1600 °C deteriorate sharply under the influences of the above two negative factors.