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

C/SiC-ZrB2 composites prepared via precursor infiltration and pyrolysis (PIP) were treated at high temperatures ranging from 1200 degrees C to 1800 degrees 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 degrees C are maximal at 216.9 MPa and 35.5 GPa, suggesting the optimal annealing temperature for mechanical properties is 1400 degrees 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 degrees 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 degrees C are merely 0.0141 g/s and 0.0161 mm/s, respectively. (C) 2013 Elsevier Ltd. All rights reserved.