Composite article and fabrication method

A refractory metal composite article includes a refractory metal ceramic section and a refractory metal ceramic coating that together form a porous matrix. A solid filler is within pores of the porous matrix to, for example, reduce a porosity of the refractory metal composite article.

BACKGROUND OF THE INVENTION

This disclosure relates to ceramic materials and, more particularly, to refractory metal ceramic composites and methods of making such materials.

Lightweight ceramic materials may have utility in a variety of different applications. Typically, ceramic materials are strong under extreme elevated temperatures and are resistant to intense thermal gradients, chemical attack, and ballistic impacts. For example, many ceramic materials exhibit resistance to temperatures above 1200° C. in combination with one or more other beneficial properties at these high temperatures.

This combination of properties makes ceramic materials attractive for many different applications. However, there are several factors that may somewhat limit the use of ceramic materials. For example, ceramic materials may be difficult to manufacture into useful shapes because they are not easily melted, machined, or formed like other material such as polymers or metals. Additionally, the composition, porosity, and other characteristics of the ceramic must be controlled through the manufacturing in order to obtain desired and useful properties in the final article. Thus, even though the potential benefits of ceramic materials are recognized, new manufacturing processes for producing desired ceramic compositions having useful shapes is desired.

Accordingly, refractory metal composites and methods of manufacturing such composites are needed.

SUMMARY OF THE INVENTION

An example refractory metal composite article includes a refractory metal ceramic section and a refractory metal ceramic coating that form a porous matrix. A solid filler is disposed within residual voids of the porous matrix. For example, the refractory metal ceramic section and the refractory metal ceramic coating each may include a refractory metal carbide, a refractory metal silicide, or a refractory metal boride.

An example method of manufacturing the refractory metal composite article includes at least partially filling the voids of the porous matrix with the solid filler to thereby reduce a porosity of the refractory metal composite article. For example, the solid filler may include a polymer, a metallic material, a glass material, or a ceramic material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1illustrates a schematic view of an example refractory metal composite article10. In the illustrated example, the article10is shown generically as having a rectangular shape, however, the refractory metal composite article10may be formed in any desired shape for a variety of different uses. For example, the refractory metal composite article10may find utility in thermal protection systems for aerospace devices, lightweight armor components, glass matrix composites, ceramic matrix composites, metal matrix composites, organic matrix composites, functionally graded ceramic containing structures, high temperature heat exchangers, high temperature filters, catalytic substrates, reactor supports, environmental barriers, components of laminate structures, and the like. As will be described below, the composition and architecture of the refractory metal composite article10are suitable for use in high temperature applications such as those mentioned above.

Referring also toFIG. 2, which schematically illustrates a cross-sectional portion, the refractory metal composite article10includes a porous matrix12having refractory metal ceramic sections14and a refractory metal ceramic coating16that coats the refractory metal ceramic sections14. As can be appreciated from the Figure, the refractory metal ceramic coating16is disposed directly adjacent to the refractory metal ceramic section14in this example. In the illustrated example, the porous matrix12comprises a fibrous structure (FIG. 1) where the refractory metal ceramic sections14are interlaced filaments coated on an exterior surface with the refractory metal ceramic coating16. A network of pores18extends between the refractory metal ceramic sections14and also between the refractory metal ceramic coating16. The fibrous, porous structure of the article10provides the benefit of having higher surface area and improved flow through the pores18compared to conventional foam structures.

A desired amount of solid filler20at least partially fills the pores18such that the article10exhibits a desired amount of residual porosity. The residual porosity may be desired for the benefit of providing a desired amount of thermal insulation, a desired amount of flow volume through the pores18of the article10, or the like. In other examples, the solid filler20may completely fill the pores18such that there is an insignificant amount of residual porosity or no residual porosity. As shown inFIG. 2, the solid filler is located on the refractory metal ceramic coating16. However, the solid filler20alternatively may partially cover the refractory metal coating16or reside as particles within the pores18, depending upon the selected manufacturing method.

Each of the refractory metal ceramic sections14, the refractory metal ceramic coating16, and a solid filler20may be selected from a variety of different materials, depending upon the intended use and desired properties of the article10. For example, the selected materials may form a composite of a refractory metal ceramic and a polymer material, a refractory metal ceramic and a metallic material, a refractory metal ceramic and a glass material, or a refractory metal ceramic and another refractory metal ceramic. Given this description, one of ordinary skill in the art will be able to select suitable materials to meet their particular needs.

The refractory metal ceramic sections14and the refractory metal ceramic coating16each include at least one refractory metal. For example, the refractory metal is silicon, hafnium, tantalum, boron, tungsten, titanium, niobium, zirconium, molybdenum, vanadium, or a combination thereof. In a further example, the refractory metal of the refractory metal ceramic sections14is in carbide form, such as silicon carbide. Likewise, the refractory metal of the refractory metal ceramic coating16may also be a refractory metal carbide. Alternatively, the refractory metal ceramic coating16may include a refractory metal silicide, or a refractory metal boride.

The solid filler20includes any of a variety of different materials, depending upon the intended use and desired properties of the article10. For example, the solid filler20may include a polymer, a metallic material, a ceramic material, or a glass material. In a further example, the ceramic material of the solid filler20is a refractory metal carbide, such as any of the above listed refractory metals in carbide form. In yet a further example, the refractory metal carbide is silicon carbide or hafnium carbide or combinations thereof, including solid solutions, which are particularly beneficial under extreme elevated temperatures.

FIG. 3illustrates an example method30for manufacturing the refractory metal composite article10of the above examples. At an initial step32, a refractory workpiece is provided. At step34, a source of the solid filler20is prepared or provided. At step36, the solid filler20is introduced within the network of pores18using a process that is suitable for the type of material selected for the solid filler20. At step38, the workpiece having reduced porosity is processed under a predetermined temperature, time, pressure atmosphere, etc., to produce the article10at final step40. Optionally, the processing at step38and step36are repeated (as indicated by the dashed lines inFIG. 3) to further reduce the porosity or deposit different types of the solid filler20, for example. Several non-limiting examples of the steps32,34,36, and38of the method30are described below.

In one example, the refractory workpiece includes the refractory metal ceramic sections14and the refractory metal ceramic coating16. For example, commonly owned U.S. application Ser. Nos. 11/455,049 and 11/567,282 disclose methods for producing a workpiece that may be used with the method30for manufacturing the article10. In other examples, the workpiece may be produced using other known methods.

In one example process for forming the workpiece, a starting material such as felt, is used. Felt is readily available, relatively low in cost, and is available in a variety of different densities. The felt may be pre-formed into a desired shape and includes a plurality of interlaced non-woven filaments, or fibers, forming a porous matrix. It is to be understood that other types of fabrics such as woven fabrics, etc., may also be used, depending upon the desired micro-architecture of the article10. The filaments are formed from a precursor material, such as carbon, but use of boron or silicon is also contemplated. A refractory metal is then deposited within the porous matrix to form a refractory metal coating on the filaments. The refractory metal is in stoichiometric excess of the precursor material of the filaments.

The refractory metal and the precursor material of the filaments are then thermally reacted to form the refractory metal ceramic sections14having a fibrous structure similar to that of the felt starting material. The thermal reaction does not require that the refractory metal be melted. Thus, this method of producing the refractory metal ceramic sections14provides the benefit of lower processing temperature compared to methods using melting. Depending upon the selected type of precursor material, the refractory metal ceramic sections include refractory metal carbide, boride, or silicide. A portion of the refractory metal remains on the refractory metal ceramic sections14because of the stoichiometric excess of refractory metal deposited originally on the filaments.

A second precursor material is then deposited adjacent the remaining refractory metal. For example, the second precursor material includes a pre-ceramic polymer. The pre-ceramic polymer and remaining refractory metal are then thermally reacted to form the refractory metal ceramic coating16on the refractory metal ceramic sections14. The resulting workpiece exhibits a fibrous structure of the refractory metal ceramic sections14coated with the refractory metal ceramic coating16. As can be appreciated, the starting materials are selected such that the above processing results in a desired composition of the workpiece, with a residual porosity due to the porous structure of the starting felt material.

To reduce the porosity to a desired level and form the composite of the article10, the pores18are then at least partially filled with the solid filler20at step36. The selected method for filling the pores18depends upon the type of material selected for the solid filler20. For example, if the solid filler20is a polymer material, a process suitable for polymer deposition is selected. If the solid filler20is a metallic material, a process suitable for metallic deposition is selected. If the solid filler20is a ceramic material, a process suitable for ceramic material deposition is selected, and if the solid filler20is a glass material or a glass ceramic (e.g., alumino-silicate glass), a process suitable for glass deposition is selected. Combinations of different types of solid fillers20and processes are also possible. A few example processes include, but are not limited to, polymer infiltration pyrolysis, glass transfer molding, chemical vapor deposition, physical vapor deposition, sol-gel, electrophoretic or electrostatic deposition, slurry deposition, dipping, vacuum filtration, freeze casting, polymer melt infiltration, molten metal infiltration, precipitation, polymerization of liquid monomers, and the like. Given this description, one of ordinary skill in the art will recognize other suitable processes to meet their particular needs.

In one example, an epoxy monomer is deposited into the pores of the workpiece (e.g., using polymer infiltration at reduced pressure). The epoxy monomer is then exposed to ultraviolet radiation for a sufficient amount of time at step38to polymerize the epoxy and thereby form the solid filler20. The resulting article10is a refractory metal ceramic—epoxy composite. Other monomers can be selected and various polymerization methods can be used, such as heating, catalysis and other wavelengths of radiation.

In another example, a pre-ceramic polymer material having a refractory metal is deposited into the pores of the workpiece. The pre-ceramic polymer is then thermally processed at step38to react the polymer and the refractory metal and thereby form a refractory metal ceramic as the solid filler20. The resulting article10is a refractory metal ceramic—refractory metal ceramic composite. The type of refractory metal ceramic produced depends upon the composition of the pre-ceramic polymer and refractory metal. For example, the refractory metal may be any of those listed above and the pre-ceramic polymer may include carbon, boron, silicon, or combinations thereof in polymeric form for reaction with the refractory metal to form carbide, boride, silicide, or combinations thereof, respectively. Alternatively, a pre-ceramic polymer without a refractory filler is used and subsequently converted into a ceramic solid filler20, such as silicon carbide. Use of pre-ceramic polymers to other silicon-containing phases such as silicon nitride, silicon carbonitride, silicon oxycarbide, silicon oxynitride, silicon-aluminum-oxygen-nitrogen (SiAION), alumino-silicates and the like is also contemplated. At step38, the temperature, heating rate, atmospheric composition, pressure, exposure time, exposure to radiation of selected wavelengths, and the like may also be controlled for effective conversion of the pre-ceramic polymer.

In another example, a metal is melted and deposited into the pores of the workpiece. The molten metal is then cooled and solidified at step38to thereby form the solid filler20. The resulting article10is a refractory metal ceramic—metal composite. The properties of the metal will preferably be selected to be compatible with the workpiece materials—e.g. it is not desirable to have the molten metal corrode the workpiece.

In another example, a glass material is deposited into the pores of the workpiece using glass transfer molding, for example. The glass material is, in its final form, a solid material having no long range crystalline order. A few example glasses include, but are not limited to, oxide based glasses such as silicates, borates, germinates, and mixtures of these. The glass is then cooled and solidified at step38to thereby form the solid filler20. The resulting article10is a refractory metal ceramic—glass composite.

In another example, a combination of more than one of a polymer, a metal, a ceramic, and a glass material is deposited into the pores of the workpiece as described above to form a hybrid refractory metal ceramic composite.

Optionally, the resulting article10or workpiece of the above examples may undergo additional processing steps to modify other characteristics, such as crystallinity, grain size, pore size, extent of porosity, etc.