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Reexamination Certificate
2000-01-21
2002-03-12
Weisberger, Rich (Department: 1774)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S299100, C501S094000, C501S095200, C264S068000, C264S068000, C264S068000, C264S068000
Reexamination Certificate
active
06355338
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to continuous composite coextrusion methods, apparatus for coextrusion, and compositions for preparing composites, such as continuous fiber reinforced ceramic matrix composites, using dense fibers and green matrices as well as to methods for the preparation of composites having interfaces between dense fibers and green matrices.
2. Background of the Invention
Composites are combinations of two or more materials present as separate phases and combined to form desired structures so as to take advantage of certain desirable properties of each component. The materials can be organic, inorganic, or metallic, and in various forms, including but not limited to particles, rods, fibers, plates and foams. Thus, a composite, as defined herein, although made up of other materials, can be considered to be a new material have characteristic properties that are derived from its constituents, from its processing, and from its microstructure.
Composites are made up of the continuous matrix phase in which are embedded: (1) a three-dimensional distribution of randomly oriented reinforcing elements, e.g., a particulate-filled composite; (2) a two-dimensional distribution of randomly oriented elements, e.g., a chopped fiber mat; (3) an ordered two-dimensional structure of high symmetry in the plane of the structure, e.g., an impregnated cloth structure; or (4) a highly-aligned array of parallel fibers randomly distributed normal to the fiber directions, e.g., a filament-wound structure, or a prepreg sheet consisting of parallel rows of fibers impregnated with a matrix.
Monolithic ceramic materials are known to exhibit certain desirable properties, including high strength and high stiffness at elevated temperatures, resistance to chemical and environmental attack, and low density. However, monolithic ceramics have one property that limits their use in stressed environments, namely their low fracture toughness. While significant advances have been made to improve the fracture toughness of monolithic ceramics, mostly through the additions of whisker and particulate reinforcements or through careful control of the microstructural morphology, they still remain extremely damage intolerant. More specifically, they are susceptible to thermal shock and will fail catastrophically when placed in severe stress applications. Even a small processing flaw or crack that develops in a stressed ceramic cannot redistribute or shed its load on a local scale. Under high stress or even mild fatigue, the crack will propagate rapidly resulting in catastrophic failure of the part in which it resides. It is this inherently brittle characteristic which can be even more pronounced at elevated temperatures, that has not allowed monolithic ceramics to be utilized in any safety-critical designs.
Research and development for these high temperature and high stress applications have focused on the development of continuous fiber reinforced ceramic matrix composites, hereafter referred to as CFCCs. The use of fiber reinforcements in the processing of ceramic and metal matrix composites is known in the prior art, and has essentially provided the fracture toughness necessary for ceramic materials to be developed for high stress, high temperature applications. See J. J. Brennan and K. M. Prewo, “High Strength Silicon Carbide Fiber Reinforced Glass-Matrix Composites,”
J. Mater. Sci.,
15 463-68 (1980); J. J. Brennan and K. M. Prewo, “Silicon Carbide Fiber Reinforced Glass-Ceramic Matrix Composites Exhibiting High Strength Toughness,” i J. Mater. Sci., 17 2371-83 (1982); P. Lamicq, G. A. Gernhart, M. M. Danchier, and J. G. Mace, “SiC/SiC Composite Ceramics,”
Am. Ceram. Soc. Bull.,
65 [2] 336-38 (1986); T. I. Mah, M. G. Mendiratta, A. P. Katz, and K. S. Mazdiyasni, “Recent Developments in Fiber-Reinforced High Temperature Ceramic Composites,”
Am. Ceram. Soc. Bull.,
66 [2] 304-08 (1987).; K. M. Prewo, “Fiber-Reinforced Ceramics: New Opportunities for Composite Materials,”
Am. Ceram. Soc. Bull.,
68 [2] 395-400 (1989); H. Kodama, H. Sakamoto, and T. Miyoshi, “Silicon Carbide Monofilament-Reinforced Silicon Nitride or Silicon Carbide Matrix Composites,”
J. Am. Ceram. Soc.,
72 [4] 551-58 (1989); and J. R. Strife, J. J. Brennan, and K. M. Prewo, “Status of Continuous Fiber-Reinforced Ceramic Matrix Composite Processing Technology,”
Ceram. Eng. Sci. Proc.,
11 [7-8] 871-919 (1990).
Under high stress conditions, the fibers are strong enough to bridge the cracks which form in the ceramic matrix allowing the fibers to ultimately carry the load, and catastrophic failure can be avoided. This type of behavior has led to a resurgence of CFCCs as potential materials for gas turbine components, such as combustors, first-stage vanes, and exhaust flaps. See D. R. Dryell and C. W. Freeman, “Trends in Design in Turbines for Aero Engines,” pp. 38-45
in Materials Development in Turbo-Machinery Design;
2nd Parsons International Turbine Conference, Edited by D. M. R. Taplin, J. F. Knott, and M. H. Lewis, The Institute of Metals, Parsons Press, Trinity College, Dublin, Ireland, 1989. CFCCs have also been given serious consideration for heat exchangers, rocket nozzles, and the leading edges of next-generation aircraft and reentry vehicles. See M. A. Karnitz, D. F. Craig, and S. L. Richlin, “Continuous Fiber Ceramic Composite Program,”
Am. Ceram. Soc. Bull.,
70 [3] 430-35 (1991), and
Flight Vehicle Materials, Structures and Dynamics—Assessment and Future Directions,
Vol. 3, edited by S. R. Levine, American Society of Mechanical Engineers, New York, 1992. In addition, CFCCs with a high level of open porosity are currently being utilized as filters for hot-gas cleanup in electrical power generation systems, metal refining, chemical processing, and diesel exhaust applications. See L. R. White, T. L. Tompkins, K. C. Hsieh, and D. D. Johnson, “Ceramic Filters for Hot Gas Cleanup,”
J. Eng. for Gas Turbines and Power,
Vol. 115, 665-69 (1993).
CFCCs are currently fabricated by a number of techniques. The simplest and most common method for their fabricating has been the slurry infiltration technique whereby a fiber or fiber tow is passed through a slurry containing the matrix powder; the coated fiber is then filament wound to create a “prepreg”; the prepreg is removed, cut, oriented, and laminated into a component shape; and the part undergoes binder pyrolysis and a subsequent firing cycle to densify the matrix. See J. J. Brennan and K. M. Prewo, “High Strength Silicon Carbide Fibre Reinforced Glass-Matrix Composites,”
J. Mater. Sci.,
15 463-68 (1980); D. C. Phillips, “Fiber Reinforced Ceramics,” Chapter 7 in
Fabrication of Composites,
edited by A. Kelly and S. T. Mileiko, North-Holland Publishing Company, Amsterdam, The Netherlands, 1983; and K. M. Prewo and J. J. Brennan, “Silicon Carbide Yarn Reinforced Glass Matrix Composites,”
J. Mater. Sci.,
17 1201-06 (1982).
Other techniques for fabricating CFCCs also typically involve an infiltration process in order to incorporate matrix material within and around the fiber architecture, e.g. a fiber tow, a preformed fiber mat, a stack of a plurality of fiber mats, or other two dimensional (2D) or three dimensional (3D) preformed fiber architecture. These techniques include the infiltration of sol-gels. See J. J. Lannutti and D. E. Clark, “Long Fiber Reinforced Sol-Gel Derived Alumina Composites”, pp. 375-81 in
Better Ceramics Through Chemistry,
Material Research Society Symposium Proceedings, Vol. 32, North-Holland, New York, 1984; E. Fitzer and R. Gadow, “Fiber Reinforced Composites Via the Sol-Gel Route”, pp. 571-608 in Tailoring Multiphase and Composite Ceramics, Materials Science Research Symposium Proceedings, Vol. 20, edited by R. E. Tressler et al., Plenum Press, New York, 1986. Other techniques include polymeric precursors which are converted to the desired ceramic matrix material through a post-processing heat treatment. See J. Jamet, J. R.
Beeaff Dustin R.
Hilmas Gregory E.
Mulligan Anthony C.
Opeka Mark M.
Rigali Mark J.
Advanced Ceramics Research, Inc.
Banner & Witcoff , Ltd.
Weisberger Rich
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