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  Continuous fiber reinforced composites and methods, apparatuses, and compositions for making the sameUSPTO Application #: 20050230029Title: Continuous fiber reinforced composites and methods, apparatuses, and compositions for making the same Abstract: A process for continuous composite coextrusion comprising: (a) forming first a material-laden composition comprising a thermoplastic polymer and at least about 40 volume % of a ceramic or metallic particulate in a manner such that the composition has a substantially cylindrical geometry and thus can be used as a substantially cylindrical feed rod; (b) forming a hole down the symmetrical axis of the feed rod; (c) inserting the start of a continuous spool of ceramic fiber, metal fiber or carbon fiber through the hole in the feed rod; (d) extruding the feed rod and spool simultaneously to form a continuous filament consisting of a green matrix material completely surrounding a dense fiber reinforcement and said filament having an average diameter that is less than the average diameter of the feed rod; and (e) depositing the continuous filament into a desired architecture which preferably is determined from specific loading conditions of the desired object and CAD design of the object to provide a green fiber reinforced composite object. (end of abstract) Agent: Banner & Witcoff, Ltd. - Chicago, IL, US Inventors: K. Ranji Vaidyanathan, Joseph Walish, Mark Fox, John W. Gillespie, Shridhar Yarlagadda, Michael R. Effinger, Anthony C. Mulligan, Mark J. Rigali USPTO Applicaton #: 20050230029 - Class: 156089110 (USPTO) Related Patent Categories: Adhesive Bonding And Miscellaneous Chemical Manufacture, Methods, Surface Bonding And/or Assembly Therefor, With Vitrification Or Firing Ceramic Material The Patent Description & Claims data below is from USPTO Patent Application 20050230029. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATION [0001] This application is a divisional of U.S. patent application Ser. No. 10/038,957, filed on Jan. 2, 2002, which claims the benefit of U.S. Provisional Application Ser. No. 60/259,284, filed on Jan. 2, 2001, and entitled "Automated Tow Placement Process for Fabricating Fiber Reinforced Ceramic Matrix Composites". These applications are incorporated herein by reference in their entirety. TECHNICAL FIELD OF THE INVENTION [0002] The present invention relates to continuous composite coextrusion methods, apparatuses 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 and apparatuses for the preparation of composites having interfaces between dense fibers and green matrices, particularly three-dimensional objects having complex geometries. BACKGROUND OF THE INVENTION [0003] 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. [0004] 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. [0005] 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. [0006] 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," 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). [0007] 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). [0008] 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). [0009] 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. Spann, R. W. Rice, D. Lewis, and W. S. Coblenz, "Ceramic-Fiber Composite Processing via Polymer-Filler Matrices," Ceram. Eng. Sci. Proc., 5 [7-8] 677-94 (1984); and K. Sato, T. Suzuki, O. Funayama, T. Isoda, "Preparation of Carbon Fiber Reinforced Composite by Impregnation with Perhydropolysilazane Followed by Pressureless Firing," Ceram. Eng. Sci. Proc., 13 [9-10] 614-21 (1992). [0010] Other research and development has involved molten metals that are later nitrided or oxidized. See M. S. Newkirk, A. W. Urquhart, H. R. Zwicker, and E. Breval, "Formation of Lanxide Ceramic Composite Materials," J. Mater. Res., 1 81-89 (1986); and M. K. Aghajanian, M. A. Rocazella, J. T. Burke, and S. D. Keck, "The Fabrication of Metal Matrix Composites by a Pressureless Infiltration Technique," J. Mater. Sci., 26 447-54 (1991). Other research and development has involved molten materials that are later carbided to form a ceramic matrix. See R. L. Mehan, W. B. Hillig, and C. R. Morelock, "Si/SiC Ceramic Composites: Properties and Applications," Ceram. Eng. Sci. Proc., 1 405 (1980). Still other research and development has involved molten silicates that cool to form a glass or glass-ceramic matrix (see M. K. Brun, W. B. Hillig, and H. C. McGuigan, "High Temperature Mechanical Properties of a Continuous Fiber-Reinforced Composite Made by Melt Infiltration," Ceram. Eng. Sci. Proc., 10 [7-8] 611-21 (1989)), and chemical vapors which decompose and condense to form the ceramic matrix (See A. J. Caputo and W. J. Lackey, "Fabrication of Fiber-Reinforced Ceramic Composites by Chemical Vapor Infiltration," Ceram. Eng. Sci. Proc., 5 [7-8] 654-67 (1984); and A. J. Caputo, W. J. Lackey, and D. P. Stinton, "Development of a New, Faster, Process for the Fabrication of Ceramic Fiber-Reinforced Ceramic Composites by Chemical Vapor Infiltration," Ceram. Eng. Sci. Proc., 6 [7-8] 694-706 (1985). [0011] Two U.S. patents have issued which involve a method for the fabrication of a fiber reinforced composite by combining an inorganic reinforcing fiber with dispersions of powdered ceramic matrix in organic vehicles, such as thermoplastics. The first patent, U.S. Pat. No. 5,024,978, discloses a method for making an organic thermoplastic vehicle containing ceramic powder that can form the matrix of a fiber reinforced composite. This patent also discloses that the ceramic powder/thermoplastic mixtures can be heated to above the melt transition temperature of the thermoplastic and then applied as a heated melt to an inorganic fiber. This patent further discloses that the process may be used to make composite ceramic articles. The second patent, U.S. Pat. No. 5,250,243, discloses a method for applying a dispersion of ceramic powder in a wax-containing thermoplastic vehicle to an inorganic fiber reinforcement material to form a prepreg material such as a prepreg tow. This patent further discloses that the prepreg tow may be subjected to a binder pyrolysis step to partially remove the wax binder vehicle prior to consolidation of the prepreg tow into the preform of a composite ceramic article. [0012] U.S. Pat. No. 5,936,861 discloses methods and apparatuses for making three-dimensional objects from continuous fiber reinforced composite materials. Slurry infiltration techniques are used to create a "prepreg" of reinforcement fiber and matrix material. The prepreg is formed into three-dimensional composite parts using a solid freeform fabrication process wherein the prepreg is extruded through a heated nozzle and deposited onto a base member and solidified. [0013] To summarize, the continuous fiber reinforced ceramic composites ("CFCCs") prior to the present invention have traditionally been fabricated using methods and apparatuses to infiltrate the matrix or matrix-forming material around a preformed architecture of dense fibers or fiber tows or by passing the fibers through a powder/melt slurry. While these methods and apparatuses provide a fiber reinforced composite structure, there is no control over the thickness of the matrix forming vehicle, and rarely will the matrix uniformly surround the fibers. In such methods, the fibers often contact each other which is detrimental to the mechanical behavior of such composites. In addition, these infiltration processes are quite slow, sometimes requiring weeks or months to fabricate components, and are severely limited in the matrix/fiber combinations that can be produced. [0014] Furthermore, currently available techniques for fabricating continuous fiber reinforced composite objects are not suited for mechanically forming fully dense objects having complex geometries from continuous fiber-reinforced filaments from ceramic powder raw materials. [0015] Thus, there exists a need for more efficient methods and apparatuses for applying the matrix to the fiber reinforcement. There exists a further need for methods and apparatuses that are versatile enough to allow almost limitless combinations of matrix and fiber reinforcement. There also exists a need for efficient methods and apparatuses for rapidly making three-dimensional objects, particularly objects having more complex geometries, from CFCCs, and particularly directly from computer aided designs (CAD). SUMMARY OF THE INVENTION [0016] The present invention comprises novel continuous composite coextrusion methods and apparatus for fabricating fiber reinforced composite materials, particularly two- and three-dimensional objects having more complex geometries. Specifically, the present invention comprises novel methods and apparatus to fabricate composite materials via an economical, versatile, tow placement process that uses filaments or tapes produced by the controlled continuous composite coextrusion process. In a particular preferred embodiment of the present invention, multiple fiber tows (bundles of fibers) are introduced during melt extrusion of a ceramic (or metal)/binder feed-rod. The result of this coextrusion process is a coextruded "green" filament or tape containing an in-situ dense fiber or tow of fibers or multiple tows of fibers. The filament or tape is further processed or laid down using methods and apparatuses for rapid deposition of the green filament to provide two- and three-dimensional objects. Preferably, the objects are formed by an automated process directly utilizing CAD drawings of such parts. [0017] More specifically, the present invention relates to processes for the rapid fabrication of a fiber reinforced composite, i.e., a composite which is comprised of a matrix of a material, such as a ceramic or metallic material, and having fibers of a ceramic material dispersed within the matrix as a reinforcement with an interface to protect the fibers from degradation during fabrication and service. A preferred method of the present invention comprises: (a) forming a material-laden composition comprising a thermoplastic polymer and at least about 40 volume % of a ceramic or metallic particulate in a manner such that the composition has a substantially cylindrical geometry and thus can be used as a substantially cylindrical feed rod; (b) forming a hole down the symmetrical axis of the feed rod; (c) inserting the start of a continuous spool of ceramic fiber, metal fiber or carbon fiber through the hole in the feed rod; (d) extruding the feed rod and fiber reinforcement simultaneously to form a continuous filament consisting of a "green" matrix material completely surrounding a dense fiber reinforcement and said filament having an average diameter that is less than the average diameter of the feed rod; and (e) mechanically depositing the continuous filament into a desired architecture to provide a green fiber reinforced composite. The green matrix may be subsequently fired, i.e., heated, to provide a fiber reinforced composite with non-brittle failure characteristics. [0018] The present invention also provides a process for the fabrication of a fiber reinforced composite having an interlayer, i.e., a composite that is comprised of a matrix of material, such as a ceramic or metallic material, having fibers of a ceramic material dispersed within the matrix as a reinforcement, and having an interlayer that is between the matrix and fiber reinforcement. This method is the same as that described in the preceding paragraph, but further comprises forming a feed rod that contains two dissimilar particulate-laden compositions wherein during the extrusion process the second particulate-laden composition forms a green interlayer between the fiber reinforcement and the green matrix in a continuous filament. This filament can be arranged as described in the previous paragraph and both the green interlayer and the green matrix may be subsequently fired to provide a fiber reinforced composite having substantially improved non-brittle failure characteristics compared to a fiber reinforced composite in the absence of an interlayer. [0019] Additionally, the present invention also provides a process for the introduction of multiple interlayers coated onto the fiber tows. This method is the same as that described in the preceding paragraph, but also includes forming a fiber tow coated with preceramic or carbon precursors to form green interlayers during the extrusion process between the fiber reinforcement and the green matrix in a continuous filament. This filament can be arranged as previously described, and both the green interlayer and the green matrix may be subsequently fired to provide a fiber reinforced composite having substantially improved non-brittle failure characteristics compared to a fiber reinforced composite in the absence of an interlayer. [0020] In a preferred method of the present invention, a co-axial filament is produced with a fiber tow surrounded by a "green" ceramic. In a further preferred embodiment of the present invention, the process has been demonstrated utilizing carbon fiber tows in a hafnium carbide ("HfC") matrix, a zirconium carbide ("ZrC") matrix, and a silicon carbide ("SiC") matrix. The resulting products can be used in extreme, high temperature environments. The fibers impart the necessary thermal shock resistance and toughness that HfC, SiC and ZrC lack as monolithic ceramics. Continue reading... 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