ations of the American Ceramic Sociery Vol 81. No. 10 30 and 50 MPa and therefore suitable to References sired fiber/matrix interaction with crack d and fiber A G. Evans and F. w. Zok, Review: The Physics and Mechanics of Fibre-Reinforced Brittle Matrix Composites, J. Mater. Sci, 29, 3857-96 So far. no substantial differences have been observed be tween sintered and annealed samples. Similar load/deflection Oxide Composites" Pais(Bordeaux, France, 199 the 6th Europ curves were obtained in both cases. A certain variety of pea naslainence stresses(interfacial strength values)may be due to inhomoge 3T. J. Mackin, J. Y. Yang, C. G. Levi, and A. G. Evans, ""Environmentally neous platinum coating of the fibers by the simple dip-coating Compatible Double Coating Concepts for Sapphire Fiber-Reinforced y-TiAl, technique, but nevertheless, the interfacial properties remain unchanged. Therefore, any degradation of the platinum inter- Composites." Am. Ceram. so;76图2y phase due to corrosion or evaporation can be neglected and SM. A. Stough, J. R. Hellmann, and M. S. Angelone, ""Interfacial Degradation stifles the expensive coating with precious metals. Looking at Ceramic Transactions, Vol 46, Chances in Ceramic- Matrir Composites .Edited the ductile deformation behavior of the platinum coating, a by J. P Singh and N P Bansal. American Ceramic Society, Westerville, OH, 1994 significant reduction of the coating thickness should be pos- " Ceramic Composites of Monazite and sible. Depending on the surface roughness of the fibers, coatin Alumina, J. Am. Ceram. Soc., 78[6] 1553-63(1995) 'D. B. Marshall, J. B. Davies, P. E. D. Morgan, and R. M. H that the precious metal is the dominant parameter. Neverthe Lake Louise, Canada, October 12-17, 1997 ss, with commercially available oxide fibers like polycrystal- B J. Dalgleish, E. Saiz, A P. Tomsia, R. M. Cannon, and R O. Ritchie line Al2O, fibers, thin platinum coatings, and the benefits of the Interface Formation and Strength in Ceramic-Metal Systems, ' Scr. Metall. RBAO process, composite prices below $700 "R K. Bordia and A Jagota, ""Crack Growth and Damage in Constrained ossible at fiber volume contents of =35% t Regarding the Sintering Films, "J.Am. Ceram Soc., 76[10]2475-85(1993) igh-temperature capabilities, such composites can have rea- oR S Hay, Fiber-Matrix Interfaces for Alumina Fiber-YAG Matrix Com- onable commercial relevance. Therefore, we think that plati IR S Hay, T May, and C. Cooke, ""Molybdenum-Palladium Fiber-Matrix num coatings represent a viable means to control the interfacial terlayers for Ceramic Composites, "Ceram. Eng. Sci. Proc., 1515] 760-68 properties of pure oxide composites for high-temperature use. (1-H w. Carpenter,JWBohlen, and w.s. Steffier,"Method of Forming a Ductile Fiber Coating for Toughening Non-oxide Ceramic Matrix Compos- IV. Conclusions ites,"U.S.Pat.No.5162271,1992 IK. L Luthra,""Ceramic Composite, "U.S. Pat. No 4 921 822, 1990 Reinforced e Using the bao technique, homogeneous fiber rein with Noble Metal Coated Ceramic Fibers. ' U.S. Pat. No 4 309 1989 orced oxide matrix co ites can be manufactured by simple ISN. Claussen, T. Le, and S. Wu, ""Low Shrinkage Reaction Bonded Alu- powder metallurgical processing and pressureless sintering Thin platinum coatings are suitable as compatible inter- ace layers between fibers and the matrix providing weak in 7J. Wendorff, R Janssen, and N. Claussen, "Model Experiments on Pure terfaces and ductile deformation behavior during fracture Oxide Composites, Mater. Sci. Eng. A, in pres These coatings are suitable for long-time use in oxygen- High Temperatures for Interface Characterization of Ceramic/Ceramic Com- ch atmospheres even at high temperatures First results indicate that very thin coatings should be posites,Pp:ng and Stan tion(Hamburg, Germany ) Edited by P. J. Hoe K Schulte, and H. Wittich. Woodhead Publishing Ltd, Cambridge, U.K., 1995. composite. Therefore, the overall price of such a composite Reinforced BAo, Ceram. Eng. san. noc. I5 5)36560(199-phire should be tolerable rained by Dens indrical Cores, Acta Metall. Mater, 37 [2]697-704(1989) ID Holz, M. Roger, R. Janssen, and N. Claussen, "Mechanical of Reaction-Bonded Al, OyZrO, Composites, " Ceram. Eng. Sci. Proc. 23J. 1. Eldridge,"Elevated Temperature Fiber Push-Out Testing, " Mater fThe calculation is based on a price for commercial fibers of about Res. Soc. Symp. Proc., 365, 283-90 er Push-Out Testing Apparatus for he market price assumed for platinum is -s 24H Janczak, L Rohr, P. Schulz, and H P, Degischer, ""Grenzflachenunt The stock market price has been in the close suchungen an endlosfaserverstarkten Aluminiummatrix Verbundwerkstoffen fur for the last 12 months die Raumfahrttechnik, ""Oberflachen, 6, 17-19(1995)30 and 50 MPa and therefore suitable to achieve the de￾sired fiber/matrix interaction with crack deflection and fiber bridging.17,22–24 So far, no substantial differences have been observed be￾tween sintered and annealed samples. Similar load/deflection curves were obtained in both cases. A certain variety of peak stresses (interfacial strength values) may be due to inhomoge￾neous platinum coating of the fibers by the simple dip-coating technique, but nevertheless, the interfacial properties remain unchanged. Therefore, any degradation of the platinum inter￾phase due to corrosion or evaporation can be neglected and justifies the expensive coating with precious metals. Looking at the ductile deformation behavior of the platinum coating, a significant reduction of the coating thickness should be pos￾sible. Depending on the surface roughness of the fibers, coating thickness down to 0.2 mm or even below should be suitable. Calculating the overall price of such a composite, it is obvious that the precious metal is the dominant parameter. Neverthe￾less, with commercially available oxide fibers like polycrystal￾line Al2O3 fibers, thin platinum coatings, and the benefits of the RBAO process, composite prices below $700/kg should be possible at fiber volume contents of ≈35%.† Regarding the high-temperature capabilities, such composites can have rea￾sonable commercial relevance. Therefore, we think that plati￾num coatings represent a viable means to control the interfacial properties of pure oxide composites for high-temperature use. IV. Conclusions ● Using the RBAO technique, homogeneous fiber rein￾forced oxide matrix composites can be manufactured by simple powder metallurgical processing and pressureless sintering. ● Thin platinum coatings are suitable as compatible inter￾face layers between fibers and the matrix providing weak in￾terfaces and ductile deformation behavior during fracture. ● These coatings are suitable for long-time use in oxygen￾rich atmospheres even at high temperatures. ● First results indicate that very thin coatings should be sufficient to achieve a damage-tolerant fracture behavior of the composite. Therefore, the overall price of such a composite should be tolerable. References 1 A. G. Evans and F. W. Zok, ‘‘Review: The Physics and Mechanics of Fibre-Reinforced Brittle Matrix Composites,’’ J. Mater. Sci., 29, 3857–96 (1994). 2 A. Kristofferson, A. Warren, J. Brandt, and R. Lundberg, ‘‘Reaction Bonded Oxide Composites’’; pp. 151–58 in Proceedings of the 6th European Conference on Composites Materials (Bordeaux, France, 1993). Edited by R. Naslain. 3 T. J. Mackin, J. Y. Yang, C. G. Levi, and A. G. Evans, ‘‘Environmentally Compatible Double Coating Concepts for Sapphire Fiber-Reinforced g-TiAl,’’ Mater. Sci. Eng., A, 161, 285–93 (1993). 4 J. B. Davis, J. P. A. Löfvander, and A. G. Evans, ‘‘Fiber Coating Concepts for Brittle-Matrix Composites,’’ J. Am. Ceram. Soc., 76 [5] 1249–57 (1993). 5 M. A. Stough, J. R. Hellmann, and M. S. Angelone, ‘‘Interfacial Degradation and Surface Modification in Zirconia-Coated Sapphire Fibers’’; pp. 839–49 in Ceramic Transactions, Vol. 46, Advances in Ceramic-Matrix Composites II. Edited by J. P. Singh and N. P. Bansal. American Ceramic Society, Westerville, OH, 1994. 6 P. E. D. Morgan, D. B. Marshall, ‘‘Ceramic Composites of Monazite and Alumina,’’ J. Am. Ceram. Soc., 78 [6] 1553–63 (1995). 7 D. B. Marshall, J. B. Davies, P. E. D. Morgan, and R. M. Housley, ‘‘Design of Ceramic Composites for high Temperature Oxidizing Environments’’; TNM5 in Proceedings of the 1st Conference on Composites at Lake Louise ’97, Lake Louise, Canada, October 12–17, 1997. 8 B. J. Dalgleish, E. Saiz, A. P. Tomsia, R. M. Cannon, and R. O. Ritchie, ‘‘Interface Formation and Strength in Ceramic–Metal Systems,’’ Scr. Metall. Mater., 31 [8] 1109–14 (1994). 9 R. K. Bordia and A. Jagota, ‘‘Crack Growth and Damage in Constrained Sintering Films,’’ J. Am. Ceram. Soc., 76 [10] 2475–85 (1993). 10R. S. Hay, ‘‘Fiber–Matrix Interfaces for Alumina Fiber–YAG Matrix Com￾posites,’’ Ceram. Eng. Sci. Proc., 14 [9–10] 922–30 (1993). 11R. S. Hay, T. May, and C. Cooke, ‘‘Molybdenum–Palladium Fiber–Matrix Interlayers for Ceramic Composites,’’ Ceram. Eng. Sci. Proc., 15 [5] 760–68 (1994). 12H. W. Carpenter, J. W. Bohlen, and W. S. Steffier, ‘‘Method of Forming a Ductile Fiber Coating for Toughening Non-oxide Ceramic Matrix Compos￾ites,’’ U.S. Pat. No. 5 162 271, 1992. 13K. L. Luthra, ‘‘Ceramic Composite,’’ U.S. Pat. No. 4 921 822, 1990. 14K. L. Luthra, ‘‘Process for Producing a Ceramic Composite Reinforced with Noble Metal Coated Ceramic Fibers,’’ U.S. Pat. No. 4 933 309, 1989. 15N. Claussen, T. Le, and S. Wu, ‘‘Low Shrinkage Reaction Bonded Alu￾mina,’’ J. Eur. Ceram. Soc., 5, 29–35 (1989). 16N. Claussen, R. Janssen, and D. Holz, ‘‘Reaction Bonding of Aluminum Oxide (RBAO) Science and Technology,’’ J. Ceram. Soc. Jpn., 103 [8] 749–58 (1995). 17J. Wendorff, R. Janssen, and N. Claussen, ‘‘Model Experiments on Pure Oxide Composites,’’ Mater. Sci. Eng. A, in press. 18J. Wendorff, R. Janssen, and N. Claussen, ‘‘The Fiber Push-Out Test at High Temperatures for Interface Characterization of Ceramic/Ceramic Com￾posites’’; pp. 69–74 in Proceedings of the 2nd European Conference on Com￾posites Testing and Standardization (Hamburg, Germany). Edited by P. J. Hogg, K. Schulte, and H. Wittich. Woodhead Publishing Ltd., Cambridge, U.K., 1995. 19J. Wendorff, D. E. Garcia, R. Janssen, and N. Claussen, ‘‘Sapphire-Fiber Reinforced RBAO,’’ Ceram. Eng. Sci. Proc., 15 [5] 364–70 (1994). 20F. F. Lange, ‘‘Densification of Powder Rings Constrained by Dense Cy￾lindrical Cores,’’ Acta Metall. Mater., 37 [2] 697–704 (1989). 21D. Holz, M. Ro¨ger, R. Janssen, and N. Claussen, ‘‘Mechanical Properties of Reaction-Bonded Al2O3/ZrO2 Composites,’’ Ceram. Eng. Sci. Proc., 15 [5] 651–58 (1994). 22J. I. Eldridge, ‘‘Elevated Temperature Fiber Push-Out Testing,’’ Mater. Res. Soc. Symp. Proc., 365, 283–90 (1995). 23J. I. Eldridge and B. T. Ebihara, ‘‘Fiber Push-Out Testing Apparatus for Elevated Temperatures,’’ J. Mater. Res., 9 [4] 1035–42 (1994). 24H. Janczak, L. Rohr, P. Schulz, and H. P. Degischer, ‘‘Grenzfla¨chenunter￾suchungen an endlosfaserversta¨rkten Aluminiummatrix Verbundwerkstoffen fu¨r die Raumfahrttechnik,’’ Oberfla¨chen, 6, 17–19 (1995). h † The calculation is based on a price for commercial fibers of about $500/kg, $10/kg for RBAO matrix, a fiber volume content of 35%, fiber diameter of 25 mm, coating thickness of 0.2 mm. This leads to an overall platinum content of 0.6 vol% of the composite. The market price assumed for platinum is ≈$14,850/kg plus 10% handling charge. The stock market price has been in the close vicinity of this value for the last 12 months. 2740 Communications of the American Ceramic Society Vol. 81, No. 10