Thermal and mechanical stabilities of Hi-Nicalon SiC fiber under annealing and creep in various oxygen partial pressures

Thermal and mechanical stabilities were investigated on Hi-Nicalon SiC fibers under annealing and creep in various oxygen partial pressures by mass change, mechanical properties as well as microstructural features. In the case of mechanical stability, the tensile strength of fiber is strongly dependent on the oxygen partial pressure of testing environment, but a weak dependence of BSR creep resistance on oxygen partial pressure is appeared. The analyses of surface morphology and mass change indicated the thermal stability of fiber under annealing in different environments was different. At different exposure temperatures and oxygen partial pressure levels, the different oxidation regimes are responsible for the strength degradation and microstructure change of fibers. Furthermore, the microstructure change is also affected by the stress applied through BSR test. This means the thermal stability of fibers is related to not only the exposed environments, but also the mechanical state of fibers.