T. Nozawa et al. Journal of Nuclear Materials 307-311(2002)1173-1177 fibers and B-Sic as matrix swells due to the lattice ex- diminished easily because of their high mobility. Con pansion by the accumulation of radiation-induced point sequently the radiation effect was slightly limited. On the defects.However at higher temperature, most of them contrary, Hi-Nicalon"M fibers are known to shrink and to increase their strength slightly by densification. How ever fiber shrinkage was also hard to occur in such a low 500 dose and high temperature irradiation for the same Neutron irradiation: 1073K, -0 4 dpa(at JMTR) eason. Similarly, proportional limit stress of all F-CVI 40 CHOI Sic/SiC was not also changed against the irradiation up CSOl to 0. 4 dpa because of good stabilities of fiber and matrix. 300 CS02 However reduction of elastic modulus of f-cvi sic Sic cannot be ignored. According to Osborne et al, the elastic modulus of B-Sic composing matrix and high crystalline Sic fibers has severe degradation against 100 Non-Irrad. Irac neutron irradiation at about 773 K up to about 0.5 dpa [5]. This degradation of stiffness was attributed to lat- Non-Irrad tice expansion of high-crystalline SiC caused by swelling mensional changes of fiber and matrix considered Displacement[mm] to be quite small in the irradiation at higher tempera tures like this experiment. From this reason, reduction Fig. 2. Stress-displacement relationships of irradiated and non- of composite stiffness seems mainly due to another irradiated F-CVI SiC/SiC composites mechanism. Possibly, degradation of F/M interface re- although the were no visible differences in fracture behaviors before 口 Elastic modulus口on% Yield Stress口 lexural strength and after neutron irradiation(Figs. 4 and 5). The F/M interface lost its load transferring function due to the degradation of PyC, which is sensitive to radiation [16]. even at low dose neutron irradiation 3. 2. Neutron effect on RS SiC/SiC Hi-NicalonTM fiber reinforced rs derived Sic matri composite with bn interphase was damaged by neutron irradiation up to 0.4 dpa(Figs. 6 and 7). All mechanical characteristics such as flexural strength, elastic modulus HNL-S/PyC/FCVI-SiC TySA/PyC/FCVI-SiC HNUPyCFCVI-Sic and proportional limit stress tended to decrease after eutron irradiation Fig. 3. Neutron irradiation effect on flexural properties of Similar to F-Cvi derived SiC matrix, rs derived Sic F-CVI SiC/SiC composites. matrix is, in general, highly crystalline. Hence, it is Cso Cso2 CHO1 RHO1 Fig. 4. Fracture appearances of non-irradiated F-CVl, RS and PIP SiC/SiC composites.fibers and b-SiC as matrix swells due to the lattice ex￾pansion by the accumulation of radiation-induced point defects. However at higher temperature, most of them diminished easily because of their high mobility. Con￾sequently the radiation effect was slightly limited. On the contrary, Hi-NicalonTM fibers are known to shrink and to increase their strength slightly by densification. How￾ever fiber shrinkage was also hard to occur in such a low dose and high temperature irradiation for the same reason. Similarly, proportional limit stress of all F-CVI SiC/SiC was not also changed against the irradiation up to 0.4 dpa because of good stabilities of fiber and matrix. However reduction of elastic modulus of F-CVI SiC/ SiC cannot be ignored. According to Osborne et al., the elastic modulus of b-SiC composing matrix and high￾crystalline SiC fibers has severe degradation against neutron irradiation at about 773 K up to about 0.5 dpa [15]. This degradation of stiffness was attributed to lat￾tice expansion of high-crystalline SiC caused by swelling. However, as mentioned previously, influences of di￾mensional changes of fiber and matrix were considered to be quite small in the irradiation at higher tempera￾tures like this experiment. From this reason, reduction of composite stiffness seems mainly due to another mechanism. Possibly, degradation of F/M interface re￾sulted in a decreasing composite stiffness, although there were no visible differences in fracture behaviors before and after neutron irradiation (Figs. 4 and 5). The F/M interface lost its load transferring function due to the degradation of PyC, which is sensitive to radiation [16], even at low dose neutron irradiation. 3.2. Neutron effect on RS SiC/SiC Hi-NicalonTM fiber reinforced RS derived SiC matrix composite with BN interphase was damaged by neutron irradiation up to 0.4 dpa (Figs. 6 and 7). All mechanical characteristics such as flexural strength, elastic modulus and proportional limit stress tended to decrease after neutron irradiation. Similar to F-CVI derived SiC matrix, RS derived SiC matrix is, in general, highly crystalline. Hence, it is 0 100 200 300 400 500 0 0.5 1 1.5 2 Displacement [mm] Flexure Stress [MPa] Irrad. Irrad. Irrad. Non-Irrad. Non-Irrad. Non-Irrad. CS01 CS02 CH01 Neutron irradiation: 1073K, ~0.4 dpa (at JMTR) Fig. 2. Stress–displacement relationships of irradiated and non￾irradiated F-CVI SiC/SiC composites. 0 0.5 1 1.5 HNL-S/PyC/FCVI-SiC (CS01) TySA/PyC/FCVI-SiC (CS02) HNL/PyC/FCVI-SiC (CH01) Irrad./Unirrad. Elastic Modulus 0.01% Yield Stress Flexural Strength Fig. 3. Neutron irradiation effect on flexural properties of F-CVI SiC/SiC composites. Fig. 4. Fracture appearances of non-irradiated F-CVI, RS and PIP SiC/SiC composites. T. Nozawa et al. / Journal of Nuclear Materials 307–311 (2002) 1173–1177 1175