R.S. Hay et al. Journal of the European Ceramic Society 20(2000)589-597 retained if those fibers were later heat-treated to higher 5. Sun, E. Y, Lin. H.-T. and Brennan, J.J., Intermediate-tempera temperatures. Again, degradation during heat-treatment ture environmental effects on boron nitride- coated silicon ca was nearly as severe in control experiments without a bide-fiber-reinforced glass-ceramic composites. J. Am. Ceram coating. Soc.,1997,80(31),609614 6. Boakye, E, Hay. R.S. and Petry. M. D. Continuous coating of Strength degradation at temperatures beneath 1200C oxide fiber tows using liquid precursors: monazite coatings on could not be caused by microstructural changes in the Nextel720.J.Am. Ceran.Soc,1999,82(9).232l-2331 fiber because there is no grain growth at those tem- 7. Morgan. P. E. D. and Marshall, D. B. Functional interfaces for peratures. An environmental cause was suggested to be oxide oxide composites. Mat Sci. Eng, 1993, A162 15-25. more likely. The chemical species in the environment or 8. Morgan, P.E. D. and Marshall, D. B, Ceramic composites of from coating degassing responsible for this degradation 9. Morgan, P. E D, Marshall, D. B and Housley, R.M,High were not successfully isolated. It is also possible that mperature stability of monazite-alumina composites. J. Ma strength degradation from the monazite coating was Sci.Eng.195,A195,215-222 related to sealing of corrosive gas decomposition pro- 10. Kanazawa, C. Johnson, S M. and Porter. J.R. Monazite coating ducts in the coating at relatively high pressure and promotes fiber pullout. J. Am. Ceram. Soc., 1997, 80(7), Back Cover I1. Kuo, D -H. and Riven, W. M, Characterization of yttrium therefore, related to transformation from open to closed phosphate and a yttrium phosphate/yttrium aluminate laminate. porosity in the coating Am. Ceran.Soc,1995,78(111),3121-3124 Lanthanum segregated from monazite to alumina 12. Goettler. R. W, Sambasivan, S. and Dravid, V.P., Isotropic mullite interphase boundaries at 1200C. Segregation omplex oxides as fiber coatings for oxide-oxide CFCC. Ceram. was associated with roughening of the fiber-coating Eng.Sci.Proc.1977,18(),279-286. 13. Davis, J. B, Marshall, D. B, Housley, R. M. and Morgan, P. E nterface and facetting of alumina grains in the fiber These microstructural changes may be at least partly responsible for low tensile strengths, but again it must 14. Hay, R.s. Davis, J.B., Marshall, D B and Morgan, P.E. D be emphasized that these tensile strengths were not much lower than those for control experiments on uncoated fibers More information on the kinetics and Hunt, A. T, Combustion chemical vapor deposition(CCVD) of LaPOa monazite and beta-alumina on alumina fibers for cerar lanthanum activity dependence for segregation are matrix composites. Mater. Sci. Eng. 4, 1998. 244, 91-96 desirable. It is clear that the tensile strength of Nextel 16. Chayka, P, personal communication. 720, with or without coating, is sensitive to processing 17. Hay, R.S., Petry, M. D. and Boakye, E.Fiber ure. furthe atings from sols and solutions Presented at the 20th Annual Conference on Composi investigation of this sensitivity is necessary to optimize processing conditions for this fiber, and to design new 18. Helmer, T, Peterlik, H and Kromp, K,Coating of carbon fibers with improved properties bers- the strength of the fibers. J. Am. Ceram. Soc., 1995 19. Parthasarathy, T.A., Folsom, C. A. and Zawada, L.P., bined effects of exposure to salt (NaCn) water and oxidatie Acknowledgements the strength of uncoated and BN- coated nicalon fibers. Ceran.Soc.,l998,81(7),1812-1818 Te thank S. Sambasivan for the monazite precursor, 20. Trumbauer, E.R. Hellmann, J.R Shelleman, D L and Ko Wilson of 3M for the Nextel 720 fiber. K. Von D. A. Effect of cleaning and abrasion induced damage on the Lehmden for thin section preparation and tensile testing. Weibull strength distribution of sapphire fiber. J. Am. Cer. Soc. 1994,77(8),2017-2024. J. Jones and P. Jero for mass spectrometry measure- 21. Inniss, D, Zhong, Q and Kurkjian, C R, Chemically corroded ments, and K. Keller for manuscript review stine silica fibers: blunt or sharp flaws. J. Am. Ceram. Soc., 1993,7612),3173-3177 22. Chang, x and Du, Y, Electrolytic treatment of continuous CVD References silicon carbide fibers. J. Am. Ceram. Soc., 1997, 80(10), 2754-2756. 23. Fernando, J.A Chawla, K. K, Ferber, M. K and Coffey, D, Effect of boron nitride coating on the tensile strength of Nextel 1. Mah. T. Mendiratta, M. G, Katz. A. P. Ruh, R. and Maz. 480fber. Mater.Sci.Eng.A,1992,154,103-108. diyasni, K. S, High-temperature mechanical behavior of fiber 24. Curtin. W. A. Strength versus gauge length in ceramic-matrix reinforced glass-ceramic-matrix composites. J. Am. Cer. Soc mposites. J. Am. Cer. Soc., 1994, 77(4). 1072-1074 1985,68(9),C248. 25. Curtin, w.A., In situ fiber strengths in ceramic-matri 2. Naslain, R, Dugne, 0, Guette, A, Sevely, J, Brosse, C. sites from fracture mirrors. J. Am. Cera. Soc.. 1994 4m4 Rocher. p and cotteret.. boron nitride i matrix composites. J. Am. Cer. Soc., 1991, 74(101), 2482-2488 26. Curtin. w.A. Ahn. B. K. and Takeda. N. d 3. Prewo. K. M. Brennan, J. J. and Starrett, S. Silicon carbide tough stress-strain behavior in unidirection amic matrIx opposites. Acta Mater., 1998, 46(10). 340 rated temperature. J. Mat. Sci., 1989, 24. 1373 27. Jones. J G.. Busbee. J. D. Jero. P. D. Kent. D. J. and 4. Zawada. L. P. and Wetherhold. R. C. The effects of thermal D. C. In situ control of interface coatings on fibers using atigue on a SIC fiber/aluminosilicate glass composite. J. Mat In: Composites and Functionally Graded Materials, ed. Sri Sci,1991,26,648-654 T.S.et al., ASME, Vol. 80, 1997, pp 379-384retained if those ®bers were later heat-treated to higher temperatures. Again, degradation during heat-treatment was nearly as severe in control experiments without a coating. Strength degradation at temperatures beneath 1200C could not be caused by microstructural changes in the ®ber because there is no grain growth at those tem￾peratures. An environmental cause was suggested to be more likely. The chemical species in the environment or from coating degassing responsible for this degradation were not successfully isolated. It is also possible that strength degradation from the monazite coating was related to sealing of corrosive gas decomposition pro￾ducts in the coating at relatively high pressure and, therefore, related to transformation from open to closed porosity in the coating. Lanthanum segregated from monazite to alumina￾mullite interphase boundaries at 1200C. Segregation was associated with roughening of the ®ber-coating interface and facetting of alumina grains in the ®ber. These microstructural changes may be at least partly responsible for low tensile strengths, but again it must be emphasized that these tensile strengths were not much lower than those for control experiments on uncoated ®bers. More information on the kinetics and lanthanum activity dependence for segregation are desirable. It is clear that the tensile strength of Nextel 720, with or without coating, is sensitive to processing conditions, environment, and temperature. Further investigation of this sensitivity is necessary to optimize processing conditions for this ®ber, and to design new ®bers with improved properties. Acknowledgements We thank S. Sambasivan for the monazite precursor, D. Wilson of 3M for the Nextel 720 ®ber, K. Von Lehmden for thin section preparation and tensile testing, J. Jones and P. Jero for mass spectrometry measure￾ments, and K. Keller for manuscript review. References 1. Mah, T., Mendiratta, M. G., Katz, A. P., Ruh, R. and Maz￾diyasni, K. S., High-temperature mechanical behavior of ®ber reinforced glass±ceramic±matrix composites. J. Am. Cer. Soc., 1985, 68(9), C248. 2. Naslain, R., Dugne, 0., Guette, A., Sevely, J., Brosse, C. R., Rocher, J. P. and Cotteret, J., Boron nitride interphase in ceramic matrix composites. J. Am. Cer. Soc., 1991, 74(101), 2482±2488. 3. Prewo, K. M., Brennan, J. J. and Starrett, S., Silicon carbide ®ber-reinforced glass ceramic composite tensile behavior at ele￾vated temperature. J. Mat. Sci., 1989, 24, 1373. 4. Zawada, L. P. and Wetherhold, R. C., The e€ects of thermal fatigue on a SIC ®ber/aluminosilicate glass composite. J. Mat. Sci., 1991, 26, 648±654. 5. Sun, E. Y., Lin, H.-T. and Brennan, J. J., Intermediate-tempera￾ture environmental e€ects on boron nitride-coated silicon car￾bide-®ber-reinforced glass±ceramic composites. J. Am. Ceram. Soc., 1997, 80(31), 609±614. 6. Boakye, E., Hay, R. S. and Petry, M. D. Continuous coating of oxide ®ber tows using liquid precursors: monazite coatings on Nextel 720. J. Am. Ceram. Soc., 1999, 82(9), 2321±2331. 7. Morgan, P. E. D. and Marshall, D. B., Functional interfaces for oxide/oxide composites. Mat. Sci. Eng., 1993, A162, 15±25. 8. Morgan, P. E. D. and Marshall, D. B., Ceramic composites of monazite and alumina. J. Am. Cer. Soc., 1995, 78(61), 1553±1563. 9. Morgan, P. E. D., Marshall, D. B. and Housley, R. M., High temperature stability of monazite±alumina composites. J. Mat. Sci. Eng., 1995, A195, 215±222. 10. Kanazawa, C., Johnson, S. M. and Porter, J. R., Monazite coating promotes ®ber pullout. J. Am. Ceram. Soc., 1997, 80(7), Back Cover. 11. Kuo, D.-H. and Kriven, W. M., Characterization of yttrium phosphate and a yttrium phosphate/yttrium aluminate laminate. J. Am. Ceram. Soc., 1995, 78(111), 3121±3124. 12. Goettler, R. W., Sambasivan, S. and Dravid, V. P., Isotropic complex oxides as ®ber coatings for oxide±oxide CFCC. Ceram. Eng. Sci. Proc., 1977, 18(3), 279±286. 13. Davis, J. B., Marshall, D. B., Housley, R. M. and Morgan, P. E. D., Machinable ceramics containing rare-earth phosphates. J. Am. Ceram. Soc., 1998, 81(8), 2169±2175. 14. Hay, R. S., Davis, J. B., Marshall, D. B. and Morgan, P. E. D., Presented at the 1998 Annual Meeting of the Am. Ceram. Soc. 15. Hwang, T. J., Hendrick, M. R., Shao, H., Hornis, H. G. and Hunt, A. T., Combustion chemical vapor deposition (CCVD) of LaPO4 monazite and beta-alumina on alumina ®bers for ceramic matrix composites. Mater. Sci. Eng. A, 1998, 244, 91±96. 16. Chayka, P, personal communication. 17. Hay, R. S., Petry, M. D. and Boakye, E. Fiber strength with coatings from sols and solutions. Presented at the 20th Annual Conference on Composites and Advanced Ceramics, Cocoa Beach, 1996. 18. Helmer, T., Peterlik, H. and Kromp, K., Coating of carbon ®bers Ð the strength of the ®bers. J. Am. Ceram. Soc., 1995, 78(1), 133±136. 19. Parthasarathy, T. A., Folsom, C. A. and Zawada, L. P., Com￾bined e€ects of exposure to salt (NaCI) water and oxidation on the strength of uncoated and BN-coated nicalon ®bers. J. Am. Ceram. Soc., 1998, 81(7), 1812±1818. 20. Trumbauer, E. R., Hellmann, J. R., Shelleman, D. L. and Koss, D. A., E€ect of cleaning and abrasion induced damage on the Weibull strength distribution of sapphire ®ber. J. Am. Cer. Soc., 1994, 77(8), 2017±2024. 21. Inniss, D., Zhong, Q. and Kurkjian, C. R., Chemically corroded pristine silica ®bers: blunt or sharp ¯aws. J. Am. Ceram. Soc., 1993, 76(12), 3173±3177. 22. Chang, X. and Du, Y., Electrolytic treatment of continuous CVD silicon carbide ®bers. J. Am. Ceram. Soc., 1997, 80(10), 2754±2756. 23. Fernando, J. A., Chawla, K. K., Ferber, M. K. and Co€ey, D., E€ect of boron nitride coating on the tensile strength of Nextel 480 ®ber. Mater. Sci. Eng. A, 1992, 154, 103±108. 24. Curtin, W. A., Strength versus gauge length in ceramic±matrix composites. J. Am. Cer. Soc., 1994, 77(4), 1072±1074. 25. Curtin, W. A., In situ ®ber strengths in ceramic±matrix compo￾sites from fracture mirrors. J. Am. Ceram. Soc., 1994, 77(4), 1075±1078. 26. Curtin, W. A., Ahn, B. K. and Takeda, N., Modeling brittle and tough stress-strain behavior in unidirectional ceramic matrix composites. Acta Mater., 1998, 46(10), 3409±3420. 27. Jones, J. G., Busbee, J. D., Jero, P. D., Kent, D. J. and Liptak, D. C. In situ control of interface coatings on ®bers using CVD. In: Composites and Functionally Graded Materials, ed. Srivatsan, T. S. et al., ASME, Vol. 80, 1997, pp. 379±384 596 R.S. Hay et al. / Journal of the European Ceramic Society 20 (2000) 589±597