126 H Liu et al/ Materials Science and Engineering A 525(2009)121-127 Matri Matrix Fiber iber Crack 20 5H Fig. 10. SEM images of physical damage to KD-2 SiC fibers during composite processing. Matrix Matrix Fiber Silicon-based oxide interphase Fig. 11. Schematic representations of the interphase structures and the matrix crack propagation paths in the KD-1 (a)and KD-2(b)SiC /SiC composites. 4. Conclusions 4. For the KD Sic fibers with high oxygen and free carbon content, a PyC fiber surface layer is an ideal choice for improving the 1. XPS and Raman analysis show that the main constituents of the mechanical properties of the Sic/Sic composites, but a silicon- surface layers of the KD-1 and KD-2SiC fibers are PyC and silicon- based oxide fiber surface layer should be avoided. based oxide, respectively. 2. The tensile strength of the KD-2 Sic fiber is about 85% that of Acknowledgements ne KD-1 SiC fiber, but the flexural strength of the KD-2 Sic/Sic composite is only around 15% that of the KD-1 SiCr/Sic composite. The authors would like to thank Processor K Jian, w. Zhou and In the KD-1 SiC /SiC composite, fiber pullout and FM debonding E Wang for help with experiments and valuable discussions re obvious, and the fiber reinforcement mechanisms are oper- able. Contrarily, the KD-2 SiC/SiC composite exhibits a standard brittle fracture behavior and fails in a catastrophic manner. References 3. The fiber surface characteristics play a key role in determining the interfacial microstructure and the degree of fiber damage [1 M. Kotani, T. Inoue, A. Kohyama, K Okamura, Y Katoh, Comp. Sci. Technol. 62 for the KD Sic/SiC composites. Due in part to the layered crys- [2] M. Kotani, T. Inoue, A Kohyama, K Okamura, Y. Katoh, Mater. Sci. Eng. A 357 tal structure, crack deflection and FM debonding occur within the Pyc interphase: at the time, the Pyc interphase PIAl 141 A19993467-47 [3 R Yamada, T. Taguchi, N Igawa. J Nucl. Mater. 283-287(2000)574-578 vides protection for SiC fibers during composite processing. All C Sutoh, S Suyama, Y Itoh, S Nakagawa, J. Nucl. Mater. 271-272 those factors endow the KD-1 Sicr/SiC composite with excellent 5I K Yoshida, M Imai, T Yano, Comp. Sci. Technol. mechanical properties. For the KD-2 SiC/SiC composite, the non tte. Acta Mater. 48( yered crystal structure of the silicon-based oxide interphase N. Yu, A Kohyama, ether with rough surface morphology results in strong inter- D.B. Marshall, B N Cox, A G. Evans. Acta Metall. 33(11)(1985)2013-2021. I bonding and serious fiber damage which makes the Kd-2 Sci.29(15)(1994) Sic/Sic composite exhibit a brittle failure behavior. Ol B. Budiansky, A.G. Evans, J.W. Hutchinson. Int J Solids Struct. 32 (3-4)(1995)126 H. Liu et al. / Materials Science and Engineering A 525 (2009) 121–127 Fig. 10. SEM images of physical damage to KD-2 SiC fibers during composite processing. Fig. 11. Schematic representations of the interphase structures and the matrix crack propagation paths in the KD-1 (a) and KD-2 (b) SiCf/SiC composites. 4. Conclusions 1. XPS and Raman analysis show that the main constituents of the surface layers of the KD-1 and KD-2 SiC fibers are PyC and silicon￾based oxide, respectively. 2. The tensile strength of the KD-2 SiC fiber is about 85% that of the KD-1 SiC fiber, but the flexural strength of the KD-2 SiCf/SiC composite is only around 15% that of the KD-1 SiCf/SiC composite. In the KD-1 SiCf/SiC composite, fiber pullout and FM debonding are obvious, and the fiber reinforcement mechanisms are oper￾able. Contrarily, the KD-2 SiCf/SiC composite exhibits a standard brittle fracture behavior and fails in a catastrophic manner. 3. The fiber surface characteristics play a key role in determining the interfacial microstructure and the degree of fiber damage for the KD SiCf/SiC composites. Due in part to the layered crys￾tal structure, crack deflection and FM debonding occur within the PyC interphase; at the same time, the PyC interphase pro￾vides protection for SiC fibers during composite processing. All those factors endow the KD-1 SiCf/SiC composite with excellent mechanical properties. For the KD-2 SiCf/SiC composite, the non￾layered crystal structure of the silicon-based oxide interphase together with rough surface morphology results in strong inter￾facial bonding and serious fiber damage, which makes the KD-2 SiCf/SiC composite exhibit a brittle failure behavior. 4. For the KD SiC fibers with high oxygen and free carbon content, a PyC fiber surface layer is an ideal choice for improving the mechanical properties of the SiCf/SiC composites, but a silicon￾based oxide fiber surface layer should be avoided. Acknowledgements The authors would like to thank Processor K. Jian, W. Zhou and F. Wang for help with experiments and valuable discussions. References [1] M. Kotani, T. Inoue, A. Kohyama, K. Okamura, Y. Katoh, Comp. Sci. Technol. 62 (2002) 2179–2188. [2] M. Kotani, T. Inoue, A. Kohyama, K. Okamura, Y. Katoh, Mater. Sci. Eng. A 357 (2003) 376–385. [3] R. Yamada, T. Taguchi, N. Igawa, J. Nucl. Mater. 283–287 (2000) 574–578. [4] A. Sayano, C. Sutoh, S. Suyama, Y. Itoh, S. Nakagawa, J. Nucl. Mater. 271–272 (1999) 467–471. [5] K. Yoshida, M. Imai, T. Yano, Comp. Sci. Technol. 61 (2001) 1323–1329. [6] F. Rebillat, J. Lamon, A. Guette, Acta Mater. 48 (2000) 4609–4618. [7] W. Yang, T. Noda, H. Araki, J.N. Yu, A. Kohyama, Mater. Sci. Eng. A 345 (2003) 28–35. [8] D.B. Marshall, B.N. Cox, A.G. Evans, Acta Metall. 33 (11) (1985) 2013–2021. [9] A.G. Evans, F.W. Zok, J. Mater. Sci. 29 (15) (1994) 3857–3896. [10] B. Budiansky, A.G. Evans, J.W. Hutchinson, Int. J. Solids Struct. 32 (3–4) (1995) 315–328