Microstructure and mechanical properties of Hi-Nicalon™ Type S fibers annealed and crept in various oxygen partial pressures

The microstructure and mechanical properties of Hi-Nicalon™ Type S fibers annealed and crept at elevated temperatures in various oxygen partial pressures were investigated. Observations and analyses of the microstructure indicated that (i) the morphologies of the fibers were heavily dependent on the oxygen partial pressure and mechanical state; (ii) the extent of fiber oxidation under creep conditions was greater in comparison to that of fibers under annealing conditions; and (iii) the transition from passive to active oxidation was accelerated by reducing the oxygen partial pressure. For the mechanical properties of fibers annealed at 1500 °C, the tensile strengths decreased with decreasing oxygen partial pressure, while the creep resistance increased slightly with decreasing oxygen partial pressure.