Effect of heat treatment on the microstructure and mechanical behavior of SiC/SiC mini-composites

The SiC/SiC mini-composites and SiC fibers (KD-I SiC fibers) were both treated at high temperature for 50 h in Ar atmosphere up to 1500 degrees C. The microstructure of fibers and composites was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The tensile test and real-time matrix crack detection were conducted to obtain mechanical behavior of the fibers and SiC/SiC composites before and after heat treatment. The parameter identification method was developed to estimate mechanical parameters of SiC/SiC composites. The results show that with increasing heat treatment temperature, fiber surfaces became coarser with the development of new defects, leading to the more dispersion of fiber tensile strength and the decrease of mean fiber tensile strength. While the matrix grains were refined and the matrix saturation crack density decreased. The interfacial shear stress also decreased after heat treatment. The correlation between the microstructure and mechanical properties of SiC/SiC composites after annealing was analyzed, and it can be found that SiC/SiC composites maintained high strength with heat treatment at temperature up to 1300 degrees C, exceeding which a sharp strength degradation by 40% was observed mainly due to the decline of fiber strength and weakening of interface.