Effects of high-temperature annealing on the microstructures and mechanical properties of C/C–ZrC–SiC composites prepared by precursor infiltration and pyrolysis

Highlights: • The ceramic phases got separated gradually as annealing temperature increased. • The heat treatment decreased the mechanical properties of the C/C–ZrC–SiC composites. • The bending fracture behavior turned to non-brittle from initially brittle. C/C–ZrC–SiC composites were fabricated by precursor infiltration and pyrolysis (PIP) process. A mixture solution of organic zirconium-containing polymer and polycarbosilane was chosen as the precursor. The porous carbon/carbon (C/C) preforms were first infiltrated in the precursor under vacuum, dried under 80 °C and then pyrolyzed at 1500 °C. After 20 cycles of PIP process, C/C–ZrC–SiC composites were obtained. The composites were further treated at 1650 °C and 1800 °C at an argon atmosphere for 2 h, respectively. The effects of high-temperature annealing on the microstructures and mechanical properties of C/C–ZrC–SiC composites were investigated. Results show that the density decreases and the different ceramic phases of the matrix get separated gradually as the annealing temperature increases. The mechanical strength decreases slightly after annealed at 1650 °C, and the downward trend is more obvious under 1800 °C in comparison to the unannealed composites. The fracture behavior of the composites changes after heat treatment. The decline of the strength and the change of the mechanical behaviors are attributed to the microstructural changes which include pores, cracks, fiber damage, weak interfacial bonding and ceramic phase separation caused by the annealing.