N Igawa et al. Journal of Physics and Chemistry of Solids 66(2005)551-554 553 7 Fig 3. Cross-sections of FCvI-SiC/SiC. the carbon thickness in the thickness range from 20 to (see Fig. 6)and it seems that multilayer was very effective 250 nm. This result shows that the thicker carbon interphase for fracture behavior. However, the tensile strength was was coated well on the surface of fibers to prevent from slightly degraded at 1300C. This degradation of Sic/Sic adhering between fiber and matrix. The fabric layer with multilayer was slightly larger than that with carbon orientation was very effective to improve the tensile interphase. No significant degradation of tensile strength in strength as shown in Fig. 5. Moreover, the tensile strength Tyranno SA fiber after annealing at 1300C in Ar was of SiC/Sic with multilayer SiC/C interphase at room reported [5]. Therefore the degradation of tensile strength of temperature was by ca. 25% larger than that with the SiC/Sic was probably caused by the partial burn-out of carbon interphase. This increment was caused by the carbon interphase near the fiber surface; this interphase multiple fracture of interphase along the carbon layers disintegration brought the less deflection of cracks at the interphase and decreased the fiber pullout during the fracture. Total thickness of carbon layers in SiC/SiC with multilayer SiC/C interphase was much greater than that with carbon interphase, therefore the greater degradation could be observed in the Sic/Sic with multilayer SiC/C interphase. More optimization of thickness of multilayer 50 Thickness of carbon(nm) Fig. 4. Effect of the thickness of carbon interphase on the tensile strength. □25°ciar 嚣1300C 30°0°30”] carbon 10 um Fig. 5. High temperature tensile strength of FCVI-SiC/SiC. Fig. 6. Fracture surface of FCVl-SiC/SiC with multilayer SiC/C interphasethe carbon thickness in the thickness range from 20 to 250 nm. This result shows that the thicker carbon interphase was coated well on the surface of fibers to prevent from adhering between fiber and matrix. The fabric layer orientation was very effective to improve the tensile strength as shown in Fig. 5. Moreover, the tensile strength of SiC/SiC with multilayer SiC/C interphase at room temperature was by ca. 25% larger than that with the carbon interphase. This increment was caused by the multiple fracture of interphase along the carbon layers (see Fig. 6) and it seems that multilayer was very effective for fracture behavior. However, the tensile strength was slightly degraded at 1300 8C. This degradation of SiC/SiC with multilayer was slightly larger than that with carbon interphase. No significant degradation of tensile strength in Tyranno SA fiber after annealing at 1300 8C in Ar was reported [5]. Therefore the degradation of tensile strength of SiC/SiC was probably caused by the partial burn-out of carbon interphase near the fiber surface; this interphase disintegration brought the less deflection of cracks at the interphase and decreased the fiber pullout during the fracture. Total thickness of carbon layers in SiC/SiC with multilayer SiC/C interphase was much greater than that with carbon interphase, therefore the greater degradation could be observed in the SiC/SiC with multilayer SiC/C interphase. More optimization of thickness of multilayer Fig. 3. Cross-sections of FCVI-SiC/SiC. Fig. 5. High temperature tensile strength of FCVI-SiC/SiC. Fig. 4. Effect of the thickness of carbon interphase on the tensile strength. Fig. 6. Fracture surface of FCVI-SiC/SiC with multilayer SiC/C interphase. N. Igawa et al. / Journal of Physics and Chemistry of Solids 66 (2005) 551–554 553