T Nozawa et aL/Journal of Nuclear Materials 384(2009)195-211 b 9苏∝ )Onm PyC case Neutron Dose [dpa-Sic] Neutron Dose [dpa-Sic c 0苏x r400C TT400 TErr=600c Turr=800C Matrix Multilane eutron Dose [dpa-Sic] b)radial stress for multilayer, (c) axial stress for monolayer and (d)axial stress for multilayer composites In calculation, radiation-induced changes in swelling and Youngs moduli of the fiber, matrix and interphase were empirically considered The effect of irradiation creep was ignored for simplicity. The fiber volume fraction and porosity are 30% and 15%, respectively. The interfacial shear strength data preliminarily defined in this The only anomaly data to be pointed out is degradation of the study therefore indicates a probable maximum shear strength at interfacial friction at 800C up to 7.7 dpa for multilayer compos- the F/M interface of irradiated Sic/SiC composites. Because of the ites. Under this irradiation condition, no serious irradiation- existence of potential irradiation-induced radial tensile es induced stress at the F/M interface is expected(Fig. 12). Alterna at the F/M interface, the interfacial shear properties may decrease. tively, the great portion of the clamping stresses is attributed to However, considering stress relaxation by irradiation creep, such the friction from the rough surface at the sliding plane As afore- degradation would be smaller than expected. An important conclu- mentioned the microstructure of PyC near the fiber is more gra sion obtained under this assumption is that the interfacial shear phitic rather than turbostratic isotropic carbon [38. possibly strength undoubtedly decreases by neutron irradiation Of particu- giving a relatively weak shear spot around graphitic PyC. Indeed, lar emphasis is that, regardless of the interface type, e.g., mono- a micrograph identified that a primary crack propagated near the yer or multilayer, the effect of neutron irradiation on interfacial fiber/interphase interface even for very thick Py C interphase com- shear properties appears to be very similar when Tirr 1000C. posites(Fig 8). For thin-layered multilayer composites, a primary Interfacial shear properties decrease first at lower neutron doses crack should propagate with a connection of two weak interfaces: and eventually approach a constant. Importantly, it can be inter- the fiber/Pyc and Py c/1st Sic matrix interfaces. This would be sup- preted as irradiation-induced change of the interfacial shear ported by the fact that flake-like Pyc debris has been observed in a strength dependent on irradiation-induced dimensional change tensile fractured surface of the multilayer composites (Fig. 13). of carbon interphase. When Tir>1000C, further deterioration of Such crack propagation produces a rough crack plane, giving nterfacial shear properties would be anticipated. strong friction at the debonded interface. It is generally reportedThe interfacial shear strength data preliminarily defined in this study therefore indicates a probable maximum shear strength at the F/M interface of irradiated SiC/SiC composites. Because of the existence of potential irradiation-induced radial tensile stresses at the F/M interface, the interfacial shear properties may decrease. However, considering stress relaxation by irradiation creep, such degradation would be smaller than expected. An important conclu￾sion obtained under this assumption is that the interfacial shear strength undoubtedly decreases by neutron irradiation. Of particu￾lar emphasis is that, regardless of the interface type, e.g., mono￾layer or multilayer, the effect of neutron irradiation on interfacial shear properties appears to be very similar when Tirr < 1000 C. Interfacial shear properties decrease first at lower neutron doses and eventually approach a constant. Importantly, it can be inter￾preted as irradiation-induced change of the interfacial shear strength dependent on irradiation-induced dimensional change of carbon interphase. When Tirr > 1000 C, further deterioration of interfacial shear properties would be anticipated. The only anomaly data to be pointed out is degradation of the interfacial friction at 800 C up to 7.7 dpa for multilayer compos￾ites. Under this irradiation condition, no serious irradiation￾induced stress at the F/M interface is expected (Fig. 12). Alterna￾tively, the great portion of the clamping stresses is attributed to the friction from the rough surface at the sliding plane. As afore￾mentioned, the microstructure of PyC near the fiber is more gra￾phitic rather than turbostratic isotropic carbon [38], possibly giving a relatively weak shear spot around graphitic PyC. Indeed, a micrograph identified that a primary crack propagated near the fiber/interphase interface even for very thick PyC interphase com￾posites (Fig. 8). For thin-layered multilayer composites, a primary crack should propagate with a connection of two weak interfaces: the fiber/PyC and PyC/1st SiC matrix interfaces. This would be sup￾ported by the fact that flake-like PyC debris has been observed in a tensile fractured surface of the multilayer composites (Fig. 13). Such crack propagation produces a rough crack plane, giving a strong friction at the debonded interface. It is generally reported Fig. 12. Calculated irradiation-induced stresses: (a) radial stress for monolayer, (b) radial stress for multilayer, (c) axial stress for monolayer and (d) axial stress for multilayer composites. In calculation, radiation-induced changes in swelling and Young’s moduli of the fiber, matrix and interphase were empirically considered. The effect of irradiation creep was ignored for simplicity. The fiber volume fraction and porosity are 30% and 15%, respectively. T. Nozawa et al. / Journal of Nuclear Materials 384 (2009) 195–211 207