T. Taguchi et al I Journal of Nuclear Materials 329-333(2004)572-576 10 Fig. 4. SEM micorophotographs of fracture surface after(a) fexural test and (b) tensile test. much smaller than that of Sic matrix. Cao reported that multi-layer was around 50 nm Table 1). Results indicate the flexural strength of Sic increased with decreasing the that 50 nm-thick C layer was thick enough for the crack grain size [16]. The strength of inner SiC layer might be deflection. The particular SiC/C multi-layer configura higher than that of Sic matrix. By the crack deflection tion in this study operated efficiently to improve the within the outer C layer, the apparent thick fibers, which mechanical properties consisted of Sic fiber and inner Sic/c layer,were formed. These apparent thick fibers were able to retain higher load compared to the Sic fibers. Furthermore 4. Conclusion the pull-out length might be increased because of the apparent thick fibers. From above reasons, the Sic/SiC composite with SiC/C multi-layer interphase mechanical strength of composite with SiC/C multi-layer coated on Tyranno SA SiC fibers was fabricated by F- was higher than that of composite with single C layer CVI process. The characterization of SiC/C multi-layer The chemical composition of fiber surface on the and the effect of Sic/C multi-layer on the mechanical fracture surface was slightly large amount of C com- properties of the composite were investigate paring to the amount of Si by EPMA evaluation. The chemical composition of fracture surface after fexural (1) The sEM and tEM observation verified that SiC/C test evaluated by epma is summarized in Table 2. The multi-layer interphase was formed on Sic fibers in analyzed points of EPMA are also given in Fig 4. This this process result indicates that the crack passed within the C layer (2)Both flexural and tensile strengths of Sic/Sic com- although the very thin C existed between SiC fiber and posite with Sic/c multi-layer interphase were first SiC layer. The reason is that the bonding strength approximately 10%o higher than that with single C between SiC fiber and C layer was high enough since the interphase surface of Tyranno SA fiber was as rough as the Sic (3)Pull-out of fiber bundles as well as pull-out of single layer(Fig. 2). fiber occurred in the composite with SiC/C multi The results of epma reveal that the crack defection occurred at almost every C layer. The SEM observation (4) Crack deflections occurred at almost every 50 nm reveals that the measured thickness of each c in the thick C layer. The particular SiC/C multi-layer con- figuration used in this study operated efficiently to improve the mechanical properties of Sic/Sic com Table posite Chemical composition of the fracture surface within SiC/C multi-layer evaluated by EPMA oints Si(at % C(at % Acknowledgements This study was carried out under the US-DOE JAERI Collaborative Program on FWB Structur Materials in Mixed-Spectrum Fission Reactors, Phase IV. This study was also supported by CREST-ACE 709 ( Core Research for Evolutional Science and Technology/ Advanced Material Systems for Energy Conversion) The analyzed poir program sponsored by the Japan Science and Technol ints were shown in Fig 4 ogy Corporation.much smaller than that of SiC matrix. Cao reported that the flexural strength of SiC increased with decreasing the grain size [16]. The strength of inner SiC layer might be higher than that of SiC matrix. By the crack deflection within the outer C layer, the apparent thick fibers, which consisted of SiC fiber and inner SiC/C layer, were formed. These apparent thick fibers were able to retain higher load compared to the SiC fibers. Furthermore, the pull-out length might be increased because of the apparent thick fibers. From above reasons, the mechanical strength of composite with SiC/C multi-layer was higher than that of composite with single C layer. The chemical composition of fiber surface on the fracture surface was slightly large amount of C com￾paringto the amount of Si by EPMA evaluation. The chemical composition of fracture surface after flexural test evaluated by EPMA is summarized in Table 2. The analyzed points of EPMA are also given in Fig. 4. This result indicates that the crack passed within the C layer although the very thin C existed between SiC fiber and first SiC layer. The reason is that the bondingstrength between SiC fiber and C layer was high enough since the surface of Tyranno SA fiber was as rough as the SiC layer (Fig. 2). The results of EPMA reveal that the crack deflection occurred at almost every C layer. The SEM observation reveals that the measured thickness of each C in the multi-layer was around 50 nm (Table 1). Results indicate that 50 nm-thick C layer was thick enough for the crack deflection. The particular SiC/C multi-layer configura￾tion in this study operated efficiently to improve the mechanical properties. 4. Conclusions SiC/SiC composite with SiC/C multi-layer interphase coated on Tyranno SA SiC fibers was fabricated by F￾CVI process. The characterization of SiC/C multi-layer and the effect of SiC/C multi-layer on the mechanical properties of the composite were investigated. (1) The SEM and TEM observation verified that SiC/C multi-layer interphase was formed on SiC fibers in this process. (2) Both flexural and tensile strengths of SiC/SiC com￾posite with SiC/C multi-layer interphase were approximately 10% higher than that with single C interphase. (3) Pull-out of fiber bundles as well as pull-out of single fiber occurred in the composite with SiC/C multi￾layer. (4) Crack deflections occurred at almost every 50 nm thick C layer. The particular SiC/C multi-layer con- figuration used in this study operated efficiently to improve the mechanical properties of SiC/SiC com￾posite. Acknowledgements This study was carried out under the US-DOE/ JAERI Collaborative Program on FWB Structural Materials in Mixed-Spectrum Fission Reactors, Phase IV. This study was also supported by CREST-ACE (Core Research for Evolutional Science and Technology/ Advanced Material Systems for Energy Conversion) program sponsored by the Japan Science and Technol￾ogy Corporation. Fig. 4. SEM micorophotographs of fracture surface after (a) flexural test and (b) tensile test. Table 2 Chemical composition of the fracture surface within SiC/C multi-layer evaluated by EPMA Analyzed points Si (at.%) C (at.%) A 51 49 B 33 67 C 47 53 D 32 68 E 41 59 F 27 63 G 30 70 H 39 61 The analyzed points were shown in Fig. 4. T. Taguchi et al. / Journal of Nuclear Materials 329–333 (2004) 572–576 575