January 1999 Creep and Fatigue Behavior in Hi-Nicalon/SiC Composites at High Temperatures 121 1300°c, Creep Creep,1300°c,Ar n=5 由 Enhanced siC/ si ◇ Standard sic/SiC 10 a Time to Rupture, s Fig. 9. Time to rupture versus stress in Hi-Nicalon TM/SiC, enhanced SiC/SiC, and standard SiC/SiC composites at 1300oC in argon. 300 104 100 106 1300 C, Creep 1300C,Air 109 Enhanced SiC/SiC Hi- 1010 TIme to Rupture,s 1000 Stress, MPa Fig. 7. Time to rupture versus stress in the Hi-Nicalon TM/SiC com- posite at 1300C in air and argo Fig. 10. Minimum creep strain rate as a function of stress in Hi- NicalonTM/SiC, enhanced SiC/SiC, and standard SiC/SiC composites in air at I300°C 300 日费 Hi-Nicalon TM/SiC Enhanced siC/SIC . o.Standard SiC/SiC SiC/SIC Stress. MPa 103 um creep strain rate as a function of stress in the TIme to Rupture,s Ites at n argon. Fig. 11. Time to rupture versus stress in the Hi-Nicalon TM/SiC, er hanced SiC/SiC, and standard SiC/SiC composites in air at 1300C. widely distributed in the specimens that have been tested in air, because the filling of the glassy phases in the cracks prohibi the diffusion of oxygen along the crack paths IV. Discussion The fiber pullout under fatigue is longer than that under creep(Figs. 19 and 20). Much debris can be observed (1) Modulus Change fracture surfaces(Fig. 20) Modulus degradation in cyclic fatigue has been reported for Figure 21 shows the fibers on the fracture surface covered by unidirectional and laminated ceramic composites at room tem- Fig 22(a). However, a large amount of glassy phases formed growth has been shown to i? emperatures.$,18,19, 21, 41Damage a layer of glassy phases. In argon, there is no fiber oxidation perature, 36-0 and elevated on the interfaces(Fig. 22(b)) CMCs under fatigue on g. w mpany a modulus decrease inwidely distributed in the specimens that have been tested in air, because the filling of the glassy phases in the cracks prohibits the diffusion of oxygen along the crack paths. The fiber pullout under fatigue is longer than that under creep (Figs. 19 and 20). Much debris can be observed on the fracture surfaces (Fig. 20). Figure 21 shows the fibers on the fracture surface covered by a layer of glassy phases. In argon, there is no fiber oxidation (Fig. 22(a)). However, a large amount of glassy phases formed on the interfaces (Fig. 22(b)). IV. Discussion (1) Modulus Change Modulus degradation in cyclic fatigue has been reported for unidirectional and laminated ceramic composites at room tem￾perature23,36–40 and elevated temperatures.5,18,19,21,41 Damage growth has been shown to accompany a modulus decrease in CMCs under fatigue loading.38,40 Fig. 11. Time to rupture versus stress in the Hi-Nicalon™/SiC, en￾hanced SiC/SiC, and standard SiC/SiC composites in air at 1300°C. Fig. 6. Minimum creep strain rate as a function of stress in the Hi-Nicalon™/SiC composite at 1300°C in air and argon. Fig. 7. Time to rupture versus stress in the Hi-Nicalon™/SiC com￾posite at 1300°C in air and argon. Fig. 8. Minimum creep strain rate as a function of stress in the Hi-Nicalon™/SiC, enhanced SiC/SiC, and standard SiC/SiC compos￾ites at 1300°C in argon. Fig. 9. Time to rupture versus stress in Hi-Nicalon™/SiC, enhanced SiC/SiC, and standard SiC/SiC composites at 1300°C in argon. Fig. 10. Minimum creep strain rate as a function of stress in Hi￾Nicalon™/SiC, enhanced SiC/SiC, and standard SiC/SiC composites in air at 1300°C. January 1999 Creep and Fatigue Behavior in Hi-Nicalon™/SiC Composites at High Temperatures 121