Effect of high-temperature annealing in air and N2 atmosphere on the mechanical properties of Si3N4 fibers

Continuous silicon nitride (Si3N4) fibers are considered as one of the most promising high-temperature wave-transparent fibers, the high-temperature performance of which need to be investigated. The Si3N4 fibers were heat-treated at elevated temperatures for different duration times in air and N2 atmosphere, respectively. The compositions, microstructures and mechanical properties were investigated by XRD, XPS, SEM and tensile strength analysis. The results show that the heat-treatment temperature, exposure time and atmosphere all have effects on the performance of the fibers. And the decrease in strength of the Si3N4 fibers annealed in N2 is due to the thermal decomposition of SixNyO and grain growth of Si3N4, while the degradation of the fibers annealed in air is mainly owing to the oxidation reactions.