Tensile properties and microstructure characterization of Hi-NicalonTM SiC fibers after loading at high temperature

Loading tests were performed on the Hi-NicalonTM fiber yarns by applying different dead loads at elevated temperatures in Ar atmosphere. After each loading test, the room temperature tensile properties of single filaments as a function of load, exposure time and temperature, were evaluated on these fibers. Strength degradation of single filament occurred after loading test, and strength retention decreased with increasing the exposure temperature and load. The microstructure observation revealed that oxidation and loading accelerated new flaw nucleation and growth resulting in stress corrosion cracks. The stress corrosion cracks acted as critical flaws and could be mainly responsible for the strength degradation. The mirror size corresponding to the critical flaw size was measured and fracture mechanics was applied to analyze failure mechanism of single filament.