Tensile behavior and microstructural characterization of SiC fibers under loading

Loading tests were performed on SiC fiber yarns by applying different dead loads at elevated temperatures in Ar atmosphere. After each loading test, the room temperature tensile properties as a function of load, exposure time and temperature, were evaluated on these fibers. Obvious strength degradation was occurred under the combined effect of exposure temperature and applied load. Meanwhile, the near stoichiometric SiC fiber, Hi-Nicalon™ Type-S, showed higher strength retention than did Hi-Nicalon™ fiber which contains excess carbon and small amount of amorphous phase. The microstructural observation revealed that the oxidation and loading accelerated new flaw nucleation and growth resulting in stress corrosion cracks. The latter acted as critical flaws and could be responsible for the strength degradation.