Effects of temperature on microstructure evolution and mechanical properties of Hi-nicalon SiC fibers

Hi-Nicalon silicon carbide fibers are mainly used as the reinforcement of the ceramic-matrix composites served for high temperature. Effects of temperature on the microstructure evolution and mechanical properties of Hi-Nicalon silicon carbide fibers were investigated, which are very important for the improvement and application of the material. Hi-Nicalon silicon carbide fibers were annealed at 1400, 1600°C and 1800°C for 10 h in an argon flow, respectively. Their microstructure was characterized by high resolution transmission electron microscope and X-ray diffraction, and the tensile strength was determined by a monofilament tensile testing machine. The results indicate that with the increasing of annealing temperatures the grain size of β-SiC is increased, the stacking faults are formed gradually and organization of the free carbon phase is increased. In addition, the tensile strength decreases with the increase of annealing temperatures. The mean strength of the fibers reduces to 1.0 GPa after annealed at 1800°C for 10 h.