826 Y Liu et al/ Corrosion Science 51(2009)820-826 SiC. 88.6%. According to previous reference [21, thermal [31 R. Naslain Rebillat. R. Pailler. F s.x. Bourrat, Boron-bearing nock would lead to the strength loss for C/SiC composites. species in ceramic matrix composites for long-term aerospace applications, J. Moreover, strength loss from thermal shock increased due 14] D.W. Mckee, Borate treatment of carbon fibres and carbon/carbon composites to the increasing temperature. Therefore, the strength los for improved oxidation resistance, Carbon 24(1986)737-741 of composites at 1200C should be mainly attributed the [5 D W. Mckee, C L Spiro, E.]. Lamby, The effects of boron additives on the mal shock influence on the composites [6IP. [7 A Derre, L Filipozzi, Ne have demonstrated the preparation and oxidation protec multilayer CVD SiC/B/SiC coatings for 3D C/SiC composite, Mater. Sci. Eng. A tion of Sic/ a-BC/SiC coatings for 3D C/SiC composites. Th [91 S J. Wu, LF. Cheng, W.B. Yang, Y.S. Liu, LT. Zhang, Y D. Xu, Oxidation prot and cross-section morphologies of the a-BC coating are ultilayer CVD SiC coatings modified by a graphitic B-Cinterlayer for 3D C/Sic nous and amorphous. The boron concentration of a-BC 5.0at%.The carbon concentration of this coating is 82.0 at.%. [10]S. Goujard andenbulcke oxida The main bonding states of boron are B-C bond and b dissolve materials protected by Si-B-C CVD coatings, Thin Solid Films 24 in graphite lattice, which condensations are 33.5 at.% and 37 at. % 111S. Goujard, L Vandenbulcke. The oxidation behaviour of two- and three- respectively. The thickness of a-BC layer is 18 um, and the thick poly layers coatings, ]. Mater. Sci. 29( ness of each Sic layer is about 25 um. [12IS. Lab H. Blanchard. R Pailler. R Naslain. En After oxidation 700. 1000. and 1200oC for 100 h in 14 vol% oxidation re of interfacial area in C/C composites. Part 1: oxidation H20/8 vol% O2/78 vol% Ar atmosphere, the weight change ratios esistance of B-C, Si-B-C and Si-C coated carbon fibres, Eur Ceram Soc. 22 e-0.49, -0.011 and 0. 14 wt%, respectively. The strength re- [131 S. Labruquere, H. Blanchard, R. Pailler. R. Naslain, Enhancement of the tained ratios of 3D C/Sic composites coated with Sic/a-BC/SiC coat- xidation resistance of interfacial area in C/C composites. Part ll: oxidation 88.6%, respectively, for SiC/SiC/Sic coatings. The strength loss /14/S. Labr. Eur. Ceram Soc. 22(2002),bon ings are 83. 2%, 96.4% and 82.6%, respectively, 65.8%, 94.9%, and comes from oxidation and thermal shock of the composites. The resistance of interfacial area in C/ c composites. Part strength loss can mainly be attributed to oxidation at 700C. The oxidation in dry or wet air on mechanical pro composites with ns.JEur. Ceram.Soc.22(2002)1023-1030. strength loss can mainly be attributed to thermal shock at [15]. Jacques, A. Guette, F. Langlais, R. in, S. Goujard, Preparation and 1200C. Therefore, the maximum value of strength retained ratio occurs at1000° Key Eng Mater.127(1997)543-550 [16] T Piquero, H. Vincent, C. Vincent, J. Boui oxidation behaviour of carbon fibres, Carbon 33(1995)455-46 Acknowledgments [17] H.T. Tsou, W. Kowbel, Design of multilayer assisted cvd coatings fo the oxidation protection of composite materials, Surf. Coat. Tech 139-150. This work was supported by the National Science Foundation in (18) E. Lamouroux, S. Bertrand, R. Pailler, R. Naslain, M Cataldi, Oxidation-resistal China(No.90405015,No.50672076,N0.50425208,No.50642039, 50820145202, 50802076). This work was also supported by the Doctorate Foundation of Northwestern Polytechnical University [191 J.P. Viricelle, P. Goursat, D. Bahloul-Hourlier, Oxidation behaviour of a multi (CX200505) [201 J. Berjonneau, G. Cholon, F. Langlais, Deposition process o Referenc arbide from CH4/BCl3/H precursor, Electrochem. Soc. 153(2006)C795- [211 S. Wu, Thermochemical environmental behaviours of 3D SiC/SiC composites, [1 R. Naslain, Design, preparation and properties of non-oxide CMcs for D thesis, North Western Polytechnical University, Xi'an, China, 2006 and nuclear reactors: an overvie chnol64(2004)155-17 [22IP. Vinicelle, P Goursat, D. Bahloul-Hourlier, Oxidation behaviour of a boron Preparation and application bases of B-c ceramic by CVD/CVL PhD arbide based material in dry and wet oxygen, Therm. Anal. Calorim. 63 thesis, North Western Polytechnical University, XI'an, China, 2008 (in Chinese). 2001)507-515SiC, 88.6%. According to previous reference [21], thermal shock would lead to the strength loss for C/SiC composites. Moreover, strength loss from thermal shock increased due to the increasing temperature. Therefore, the strength loss of composites at 1200 C should be mainly attributed ther￾mal shock influence on the composites. 4. Conclusions We have demonstrated the preparation and oxidation protec￾tion of SiC/a-BC/SiC coatings for 3D C/SiC composites. The surface and cross-section morphologies of the a-BC coating are homoge￾nous and amorphous. The boron concentration of a-BC coating is 15.0 at.%. The carbon concentration of this coating is 82.0 at.%. The main bonding states of boron are B–C bond and B dissolved in graphite lattice, which condensations are 33.5 at.% and 37 at.%, respectively. The thickness of a-BC layer is 18 lm, and the thick￾ness of each SiC layer is about 25 lm. After oxidation 700, 1000, and 1200 C for 100 h in 14 vol.% H2O/8 vol.% O2/78 vol.% Ar atmosphere, the weight change ratios are 0.49, 0.011 and 0.14 wt.%, respectively. The strength re￾tained ratios of 3D C/SiC composites coated with SiC/a-BC/SiC coat￾ings are 83.2%, 96.4% and 82.6%, respectively, 65.8%, 94.9%, and 88.6%, respectively, for SiC/SiC/SiC coatings. The strength loss comes from oxidation and thermal shock of the composites. The strength loss can mainly be attributed to oxidation at 700 C. The strength loss can mainly be attributed to thermal shock at 1200 C. Therefore, the maximum value of strength retained ratio occurs at 1000 C. Acknowledgments This work was supported by the National Science Foundation in China (No. 90405015, No. 50672076, No. 50425208, No. 50642039, 50820145202, 50802076). This work was also supported by the Doctorate Foundation of Northwestern Polytechnical University (CX200505). References [1] R. Naslain, Design, preparation and properties of non-oxide CMCs for application in engines and nuclear reactors: an overview, Compos. Sci. Technol. 64 (2004) 155–170. [2] Y.S. Liu, Preparation and application bases of B–C ceramic by CVD/CVI. PhD thesis, North Western Polytechnical University, Xi’an, China, 2008 (in Chinese). [3] R. Naslain, A. Guette, F. Rebillat, R. Pailler, F. Langlais, X. 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