Microstructure evolution and failure mechanism of 2D C_f/SiBCN–ZrB₂ composite at elevated temperatures

SiBCN ceramic has already been widely used in the thermal insulation field. To further enhance their mechanical properties in high-temperature environments, the preparation of SiBCN and ZrB₂ based pyrolytic carbon (PyC) modified carbon fiber reinforced composite, i.e., 2D C_f/SiBCN–ZrB₂, was proposed in this study. By using five cycles of polymer impregnation and pyrolysis (PIP), the composite could be synthesized with a high flexural strength at room temperature, i.e., 275 ± 15 MPa. To understand the evolution of the microstructure caused by high temperatures and their influences on the mechanical properties, the composite samples were heat treated at 1200, 1400, 1600, and 1800 °C for 2 h, respectively. Comparing the flexural strengths of the samples before and after the heat treatments, and meanwhile combining the advanced microstructural characterizations, it was found that the composite was stable when the treating temperature was below 1400 °C, i.e., the flexural strength was 250 ± 15 MPa with a strength retention rate of over 90 %. However, once the temperature was above 1600 °C, due to the crystallization of SiBCN–ZrB₂ matrix, the pyrolysis of PyC interfaces, the carbothermal reduction reaction and the erosion of carbon fibers, the mechanical properties of the composite would reduce to 74 ± 9 MPa. This study provides a new method for preparing 2D C_f/SiBCN–ZrB₂, which reduces the number of PIP cycles of composite materials and enables rapid prototyping of composite materials. Additionally, this research can help materials scientists understand the mechanical properties of 2D C_f/SiBCN–ZrB₂ composite materials in high-temperature environments and the evolution of their microstructure, identifying the range of application temperatures for 2D C_f/SiBCN–ZrB₂.