Oxidizing environment infuence on 2D-SiC)BN/SiC composites propagating through the material. The decrease of4.Evans and marshall. d. B. The mechanical beha- the mechanical properties at high temperature is vior of ceramic matrix composites. Acta Metall., 1989, 37 mainly attributed to the evolution of the carbon 256783. 5. Kerans, R.J., Jay,RS. Pagano, N J and Parthasarathy rich interfaces leading to the main formation of T.A. The role of the fiber matrix interface in ceramic silica and consequently to a stronger fiber/matrix composites. Am. Ceram. Soc. Bull, 1989, 68, 429-442 bonding. This evolution can be slowed down by 6. Brennan, J. J, Interfacial studies of chemical-vapor-infil controlling the access of oxygen till the oxidizible trated ceramic matrix composites. Mat. Sci. and Eng, 1990,A126,203-223 ayers. Thinner BN interphase decreases the inter 7. Naslain, R, Fibre-matrix interphases and interfaces in facial shear resistance and mainly the crack den- ceramic matrix composites pro by CVi. Composite sily. Thus, interfacial properties of materials with 8. Lowden. R Schwarz, O.J. and More. K. L small Bn thicknesses, even if they are initially lower are less changed and a better thermomechanical Cerarn. Eng. Sci. Proc, 1993, 14, 375-384 resistance to static and dynamic constraints Bacos, M. P, Carbon-carbon composites: oxidation obtained. The classical Sic/c/SiC materials which sup.J.Phys.I,1993,3,1895-1903 have a much higher interfacial shear resistance still 10. Vandenbulcke, L and Leparoux, M, Silicon and boron exhibit a better behavior under dynamic fatigue at ntaining components by CVD and CVI for high ten- 600C in air, while being more oxidizible. It appears perature ceramic composites. Phys. /V, Colloque C5, 1995,735-751 then of prime importance to increase greatly the ll. Grande, D H, Fibre-matrix bond strength studies of interfacial sliding resistance of SiC/BN/SiC com glass, ceramic, and metal matrix composites. J. Mat. Sci, posites to improve both the static and the dynamic 12. Leparoux, M, Vandenbulcke, L, Goujard, s, Robin- behaviors of such materials. On the other hand it Brosse, C. and Domergue, J M.. Mechanical behavior of would be interesting to prevent the formation of 2D-SiC/BN SiC processed by ICVI. In Proc. Tenth Int carbon-rich interfaces resulting from the fiber Conf on Composite Materials, Vol IV,ed. A. Poursatip and K Street. woodhead, Cambridge, UK, 1995 pp 633-40 treatment and from the sic / matrix infiltration 13. Droillard. C. Elaboration et car Finally, further studies should consider the sites a matrice SiC et a interphase sequence C/SiC. Ph. D influence of the temperature on the interfacial thesis, Bordeaux University, franc propertics and the damaging modes of the materi- 14. Kmetz. M. A. Laliberte. J. M. willis, W. s and Suib S. L, Synthesis, characterization, and tensile strength of als. If the oxygen access parallel to the fibers CVI SiC/BN/ SiC composites. Ceram. Eng. Sci. Pro through the BN interphase itself is important, the 991,12.2161-2174 bn purity, its organization and oxidation resis 15. Leparoux, M, Serin, V, Vandenbulcke, L and Sevely, J TEM and EELS studies of the interphase and interfaces tance should be improved, and multi-sequenced microstructure and chemistry of SiC/BN/SiC composites interphases that include thin BN sub-layers should processed by ICVI. J. Mat Sci., 1997, 32, 4591-4602. CVD and ICVI processes on the boron nitride deposition kinetics. In Proc. of the Xlll Int. Conf. on Chemical Vape Acknowledgements Robinson and R. K. Ulrich, The Electrochem. Society. Pennington, N, 1996, pp 594-599 17. Dambrine, B and Gauthier, G, Role de I'oxydation sur le This research has been supported by the Societe comportement en fatigue du osite Sic/SiC. Revue Europeenne de Propulsion and by the Region des composites et des materiaux avances, 1993, 3, 207-223 Centre through a grant given to M. Leparoux. The 18. Cutard, T, Caracterisation ultrasonore a haute temperature et sous contraintes de traction de composites ceramique authors acknowledge J. Gouineau and G. Lama zouade from SEP for the mechanical characteriza- /9 ceramique Ph. D thesis, Limoges University, France, 1993 tions and for the SEM observations, respectively des fibres et de la zone interfacial fibre matrice sur le co portement mecanique des composites Sic/C/SiC et SiC/ AS-L apres vieillissement thermique sous atmos controlee, Ph D. thesis, Bordeaux University, France, 199 References 20. Stephan, O, Ajayan, P. M, Colliex, C,, Redlich, P. H Lambert, J M, Bernier, P and Lefin, P,, Doping graphite I. Jouin, J. M., Cotteret, J and Christin, F. Sic-Sic inter- and carbon nanotube structures with boron and nitrogen hases case history. In Proceeding s of the 2nd europe Science,1994,266,l683-1685 Designing Ceramic Interfaces: Under- 21. Egerton, R. F,, Electron Energy-Loss Spectroscopy in the anding and tailoring interfaces for Coating, Composite 22. Kun ron Microscope. Plenum Press, New York, 1986 and Joining Applications, ed S. D. Peteves, CEE, Petten, 22. Kundman, M, EL/ P Software Instruction Manual. Gatan Netherlands, 1 1-13 November 1991, pp. 191-204 c,1993 CVD/CVI Pulse aux materiaux composites thermostructuraux. Ph. D thesis nology, Vol 3, Viscosity and Relaxation, ec Bordeaux University, france, 1993 nann and n.. Kreidl. Academic press. Inc. Orlando 3. Leparoux, M, Vandenbulcke, L. and Clinard, C, Influ 1986,p.245 ence of isothermal CVD and Cvi processes on the 24. Rockett, T. J. and Foster. W. R. Phase relations in the nitride deposition kinctics and microstructure, Submitted system boron oxide silica. J. Am. Ceram. Soc, 1965, 48, to j. Am. Ceram. sc 7580.Oxidizing environment influence on ZD-SiCIBNjSiC composites 123 propagating through the material. The decrease of the mechanical properties at high temperature is mainly attributed to the evolution of the carbon￾rich interfaces leading to the main formation of silica and consequently to a stronger fiber/matrix bonding. This evolution can be slowed down by controlling the access of oxygen till the oxidizible layers. Thinner BN interphase decreases the inter￾facial shear resistance and mainly the crack den￾sity. Thus, interfacial properties of materials with small BN thicknesses, even if they are initially lower, are less changed and a better thermomechanical resistance to static and dynamic constraints is obtained. The classical Sic/C/Sic materials which have a much higher interfacial shear resistance still exhibit a better behavior under dynamic fatigue at 600°C in air, while being more oxidizible. It appears then of prime importance to increase greatly the interfacial sliding resistance of SiC/BN/SiC com￾posites to improve both the static and the dynamic behaviors of such materials. On the other hand, it would be interesting to prevent the formation of carbon-rich interfaces resulting from the fiber treatment and from the Sic/matrix infiltration. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. Finally, further studies should consider the influence of the temperature on the interfacial properties and the damaging modes of the materi￾als. If the oxygen access parallel to the fibers through the BN interphase itself is important, the BN purity, its organization and oxidation resis￾tance should be improved, and multi-sequenced interphases that include thin BN sub-layers should be studied. 14. 15. 16. Acknowledgements 17. This research has been supported by the Societe Europeenne de Propulsion and by the Region Centre through a grant given to M. Leparoux. The authors acknowledge J. Gouineau and G. Lama￾zouade from SEP for the mechanical characteriza￾tions and for the SEM observations, respectively. 18. 19 References 20. Jouin, J. M., Cotteret, J. and Christin, F., SiCSiC inter￾phases case history. In Proceedings of the 2nd European Colloquium on Designing Ceramic Interfaces: Under￾standing and tailoring interfaces for Coating, Composite and Joining Applications, ed. S. D. Peteves, CEE, Petten, Netherlands, 11-13 November 1991, pp. 191-204. Dupel, P., CVDjCVI pulsee du pyrocarbone: application aux materiaux composites thermostructuraux. Ph.D. thesis, Bordeaux University, France, 1993. Leparoux, M., Vandenbulcke, L. and Clinard, C., Influ￾ence of isothermal CVD and CVI processes on the boron nitride deposition kinetics and microstructure. Submitted to J. Am. Ceram. Sot. 21. 22. 23. 24. Evans, A. G. and Marshall, D. B., The mechanical beha￾vior of ceramic matrix composites. Acta Metall., 1989, 37, 256783. Kerans, R. J., Jay, R. S., Pagano, N. J. and Parthasarathy, T. A., The role of the fiber matrix interface in ceramic composites. Am. Ceram. Sot. Bull, 1989, 68, 429-442. Brennan, J. J., Interfacial studies of chemical-vapor-infil￾trated ceramic matrix composites. Mat. Sci. and Eng, 1990, A126,203-223. Naslain, R., Fibre-matrix interphases and interfaces in ceramic matrix composites processed by CVI. Composite Interfaces, 1993, 1, 253-286. Lowden, R. A., Schwarz, 0. J. and More, K. L., Improved fiber coatings for Nicalon/SiC composites. Ceram. Eng. Sci. Proc, 1993, 14, 375-384. Bacos, M. P., Carbon-carbon composites: oxidation behavior and coatings protection. J. Phys. IV, ~011. C7, supl. J. Phys. ZZI, 1993, 3, 1895-1903. Vandenbulcke, L. and Leparoux, M., Silicon and boron containing components by CVD and CVI for high tem￾perature ceramic composites. J. Phys. IV, Colloque C5, 1995, 735-751. Grande, D. H., Fibre-matrix bond strength studies of glass, ceramic, and metal matrix composites. J. Mat. Sci, 1988,23, 311-328. 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Egerton, R. F., Electron Energy-Loss Spectroscopy in the Electron Microscope. Plenum Press, New York, 1986. Kundman, M., EL/P Software Instruction Manual. Gatan Inc., 1993. Scholze, H. and Kreidl, N. J., Glass-Science and Tech￾nology, Vol. 3, Viscosity and Relaxation, ed. D. R. Uhl￾mann and N. J. Kreidl, Academic Press, Inc., Orlando, FL, 1986, p. 245. Rockett, T. J. and Foster, W. R., Phase relations in the system boron oxide-silica. J. Am. Ceram. Sot, 1965, 48, 7580