Effects of high-temperature annealing on the microstructure and properties of C/SiC–ZrB2 composites

Abstract

C/SiC–ZrB2 composites prepared via precursor infiltration and pyrolysis (PIP) were treated at high temperatures ranging from 1200°C to 1800°C. The mass loss rate of the composites increased with increasing annealing temperature and the flexural properties of the composites increased initially and then decreased reversely. Out of the four samples, the flexural strength and the modulus of the specimen treated at 1400°C are maximal at 216.9MPa and 35.5GPa, suggesting the optimal annealing temperature for mechanical properties is 1400°C. The fiber microstructure evolution during high-temperature annealing would not cause the decrease of fiber strength, and moderate annealing temperature enhanced the thermal stress whereas weakened the interface bonding, thus boosting the mechanical properties. However, once the annealing temperature exceeded 1600°C, element diffusion and carbothermal reduction between ZrO2 impurity and carbon fibers led to fiber erosion and a strong interface, jeopardizing the mechanical properties of the composites. The mass loss rate and linear recession rate of composites treated at 1800°C are merely 0.0141g/s and 0.0161mm/s, respectively.