The effect of high-temperature annealing on tensile strength and its mechanism of Hi-Nicalon SiC fibres under inert atmosphere
Hi-Nicalon SiC (silicon carbide) fibres were annealed in an argon flow for 10 h at 1400 °C, 1600 °C and 1800 °C. The strength of the fibres was determined by a monofilament tensile testing machine, their fracture surfaces were analysed by SEM (scanning electron microscope) and their microstructure was characterized by a TEM (transmission electron microscope) and XRD (X-ray diffractometer). The results indicated that the strength of the fibres obeyed the Weibull distribution and the tensile strength decreased with the increase of annealing temperatures. The specimens showed brittle/flat fracture; most of the cracks initiated at the inner region of the fibres. After being annealed at 1800 °C for 10 h, the specimens showed cleavage and transcrystalline fracture. Statistical analysis revealed that the defects at the surface of the fibres had a negligible effect on their strength.