60/511,572, filed on October 14,2003. The disclosure of that commonly owned patent application is hereby incorporated by reference in its entirety.

TECHNICAL FIELD [0002] The present invention relates to metal-ceramic composite bodies, especially such composite bodies made by infiltrating a porous mass of one or more reinforcement materials with a molten infiltrant containing silicon metal. More exactly, the present invention pertains to methods for producing hollow passageways, or channels, possibly but not necessarily open at both ends, within the composite body.

BACKGROUND ART 1. Discussion of Related Art of Others [0003] A number of commercially valuable metal-ceramic composite materials are made by an infiltration route. Among the more interesting of these are those that do not require large applications of pressure, such as is required for the so-called squeeze casting technique.

[0004] Among those infiltration processes that have been around for decades is that of silicon melt infiltration, whereby molten silicon metal is caused to infiltrate a porous mass of ceramic material such as silicon carbide or silicon nitride. In one common variation of this basic process, the porous mass, which is often silicon carbide particulate, also contains a quantity of carbon. A variety of carbonaceous precursors can be used to introduce this carbon into the preform such as pitch, phenolics, furfuryl alcohol, carbohydrates such as sugars, etc.

[0005] Next, the preform containing the reinforcement and the precursor is"carbonized"in an inert atmosphere above 600°C to convert the precursor to carbon. Finally, the preform is placed in contact with a molten infiltrant material featuring Si metal or alloys of Si in an inert or vacuum atmosphere and heated to above the melting point of the infiltrant material. Due to inherent wetting and reaction between carbon and molten Si, the preform is infiltrated completely. The carbon in the preform reacts with the Si, forming some in-situ SiC, and in the process bonds the reinforcement together. Thus, this in-situ SiC typically is interconnected. A dense body usually is desired, so the process typically occurs in the presence of excess silicon.

The resulting composite body thus comprises silicon carbide and unreacted silicon (which typically also is interconnected), and may be referred to in shorthand notation as Si/SiC or RBSC (denoting"reaction-bonded silicon carbide"). Other terms such as"self-bonded SiC", reaction forming","reactive sintering", etc. , are also abundant in the literature. Among the early practitioners of this technology are Popper (U. S. Patent No. 3,275, 722), Taylor (U. S.

Patent No. 3,205, 043), andHillig (U. S. Patent No. 4,184, 894).

[0006] More recently, Chiang et al. (U. S. Patent No. 5,509, 555) disclosed the production of silicon carbide composite bodies using a silicon alloy infiltrant. The preform to be infiltrated by the alloy can consist of carbon or can consist essentially of carbon combined with at least one other material such as a metal like Mo, W, or Nb; a carbide like SiC, TiC, or ZrC; a nitride like Si3N4, TiN or A1N ; an oxide like Zr02 or A1203 ; or an intermetallic compound like MoSi2 or WSi2, or mixtures thereof. The liquid infiltrant includes silicon and a metal such as aluminum, copper, zinc, nickel, cobalt, iron, manganese, chromium, titanium, silver, gold, platinum and mixtures thereof.

[0007] U. S. Patent No. 3,857, 744 to Moss discloses the use of boron nitride powder to help define a shape or surface of a composite silicon impregnated boron carbide body. In particular, Moss discloses that coating a surface of a preform with the boron nitride powder prevents silicon metal from depositing or adhering to that surface. After infiltration of the preform, the boron nitride powder can be readily removed.

[0008] U. S. Patent No. 5,125, 822 to Kasprzyk discloses an"insulating material", which is defined as"one that is not wetted by molten silicon, that is, is not silicon infiltrated."The insulating material functions to provide physical support for the RBSC structure being formed, insulate the furnace tube from high temperatures and allow the final RBSC structure to be easily removed from the furnace tube. Boron nitride, aluminum nitride, silicon nitride, and oxides such as aluminum oxide zirconium oxide and fused quartz are useful insulating materials.

[0009] U. S. Patent No. 5,361, 824 to Keck et al. discloses the use of a"shape defining means" for use in conjunction with the production of metal matrix composites (MMCs), particularly in the context of the spontaneous infiltration of aluminum-based alloys into permeable ceramic preforms. The matrix metal alloy infiltrates up to, but not into, the shape defining means.

Upon removal of the shape defining means, a hollow or void is left in the MMC body having the inverse shape as the shape defining means. This technique can be used to make cavities, or channels in MMC bodies. The shape defining means can be material that is substantially non- infiltratable under the process conditions, such as ceramic particulate not containing an infiltration enhancer material.

[0010] The manufacture of silicon-infiltrated composite structures containing channels or cavities within the structure often presents special challenges. Often times, for example, and particularly when the infiltrant material contains high proportions of silicon, the wetting and/or infiltrating power of these infiltrants can be so great that the cavities or channels tend to become partially to completely occluded with the infiltrant during preform infiltration. Boron nitride, a substance known to resist infiltration by pure silicon metal, is not the complete solution. For example, sometimes the end-use application for the silicon-infiltrated component dictates that the component not come in contact with sources of boron during processing.

Other times, boron nitride loses its effectiveness as a non-infiltratable material, particularly against aluminum-containing molten infiltrants. The known art does not seem to provide a solution.

2. Discussion of Commonly Owned Patents and Patent Applications [0011] Many embodiments of making metal-ceramic composite bodies by means of infiltration of molten silicon are in the public domain. However, in recent years, this approach has been further enhanced by M Cubed Technologies, Inc. ("M Cubed") for making silicon- infiltrated composite bodies that optionally feature different or additional reinforcements such as boron carbide or carbon fibers, or feature one or more alloying elements such as aluminum, copper, molybdenum, boron, etc. See, for example, U. S. Patent Nos. 6,355, 340 to Singh et al. , and 6,503, 572 to Waggoner et al. , and PCT Publication No. WO 02/068,373. M Cubed currently makes commercial components using reaction bonding. The shrinkage from the beginning to the end of the process typically is quite small, which permits net-shape component fabrication. In addition, the carbonized performs can be green machined to high tolerances, bonded together, and infiltrated with a silicon- containing metal to make composite bodies having complex shapes.

[0012] Waggoner in particular teaches the use of"bedding materials"for supporting the porous mass to be infiltrated. In general, the bedding material is a material that is substantially non-infiltratable under the local process conditions. The use of a bedding material dispenses with the need to place the porous mass in direct contact with the container that houses the porous mass and the molten silicon. Such direct contact often resulted in reaction between the molten silicon and the container material. Although SiC is a common filler for the porous mass, under certain conditions such as relatively low temperature and/or noble gas atmosphere, it cannot be infiltrated easily by molten silicon without the additional presence of some free (i. e., reactable) carbon. Thus, under such conditions, an acceptable bedding material can be SiC particulate that does not also contain such free carbon.

[0013] The entire contents of these commonly owned patents and patent applications are herein incorporated by reference in their entirety.

OBJECTS OF THE INVENTION [0014] Thus, in view of the present state of materials development, it is an object of the instant invention to produce a metal-ceramic composite material using molten silicon infiltration that contains one or more cavities, but without having to form such cavities by machining following the manufacturing of the composite body.

[0015] It is an object of the instant invention to provide a perform containing one or more cavities, or green machined to contain one or more cavities, or forming one or more cavities by joining two or more smaller preform subunits together, and to infiltrate such a preform or bonded preform subunits to produce a composite body while preserving the cavities in the formed composite body.

[0016] It is an object of the instant invention to provide a means for preventing molten infiltrant from swelling or expanding into the formed cavity upon freezing of the infiltrant.

[0017] It is an object of the instant invention to be able to easily, inexpensively and readily remove from the formed article the material that prevents the cavity from being blocked with infiltrant material.

DISCLOSURE OF THE INVENTION [0018] In the context of the composite materials systems made by infiltration of molten silicon, these and other objects of the present invention are achieved by providing a preform containing at least one cavity, or an assemblage of subunit preforms joined together to provide or define at least one cavity. A material that remains not infiltratable by the molten infiltrant material is contacted to substantially all interior surfaces, e. g. , walls, of the cavity. The contacting can consist essentially of a coating on the walls, or may consist of substantially filling up the cavity with the non-infiltratable material, or some variation in between.

Preferably, the non-infiltratable material is in a form that can be readily removed following processing, such as a loosely bound, or even a free-flowing mass of particulate. The preform or subunit assemblage may then be infiltrated with the molten infiltrant material in the normal way. The infiltrant does not infiltrate into the cavity, it being locally stopped by the non- infiltratable material at the walls of the cavity. Following solidification of the infiltrant to form a silicon-infiltrated composite body, the non-infiltratable material is removed readily, since it is still in a loose, or loosely bonded condition, thus, it can be removed by air or water jets, shaking, vacuuming, etc. To assist in the removal, for example, where the cavity is intended to be entirely closed, one may machine one or more access ports so that the cavity is temporarily in communication with the exterior of the silicon-infiltrated composite body, and thereby providing access to the pressure jet or vacuum means. Once the non-infiltratable material has been removed to a desired extent, any such temporary access ports may be re-closed or resealed, for example with a thermoplastic or thermosetting polymer.

BRIEF DESCRIPTION OF THE FIGURES [0019] Figures 1A through 1C illustrate in schematic form three different types of cavities that can be produced in metal-ceramic composite bodies according to the instant invention.

[0020] Figure 2 is a photograph of a plate or block of RBSC composite material containing four at least partially occluded cooling channels, and one open channel.

[0021] Figure 3 is a schematic view of an infiltration bonded cooling plate having an internal serpentine cooling channel.

MODES FOR CARRYING OUT THE INVENTION [0022] The instant invention describes how to produce a silicon-infiltrated composite body containing one or more intentional cavities, engineered"internal cavities". A non-limiting exemplary number of such cavities are shown in Figure 1, each of which is encompassed by the instant invention. In each embodiment, the preform is assembled from two subunit preforms, perhaps being joined to one another through an adhesive bond, but ultimately becoming a unitary structure upon infiltration. In each embodiment, the lower 11 subunit features a cavity 13 of some sort, and the upper subunit 15 attaches to the lower preform subunit to provide a top surface of the cavity, thereby closing off this side of the cavity to the environment outside of the assembled preform.

[0023] With specific reference to Figure 1A, what is shown is an internal cavity that extends completely through the composite body. This cavity has an entrance region 21 and an exit region 23. In Figure 1B by contrast, the cavity is"blind"in that it does not extend all the way through the composite structure. It does not have separate entrance and exit regions. In Figure 1 C, the cavity has neither an entrance nor an exit region; it has no opening to the exterior of the composite structure. It is completely enclosed. The engineered cavities resulting from the Figure 1A and 1B embodiments can also be produced using a single preform body, that is, by green machining, for example.

[0024] The manufacture of silicon infiltrated composite structures containing channels or cavities within the structure often presents special challenges. Sometimes, such as when the infiltrant consists of a silicon-aluminum alloy containing about 40 to 60 percent by volume of aluminum, no special procedures are required, and the infiltrant can possibly infiltrate the preform up to, but not into, the channel. Most other infiltrant compositions, however, and particularly those containing higher proportions of silicon, will tend to infiltrate or occlude the channel, thus requiring the artisan to take one or more deliberate steps to prevent this from happening. There are a number of materials that in porous form resist or tend to resist being infiltrated by silicon-containing melts. The best choice of such infiltration-resisting or infiltration-halting material depends on several considerations. Thus, it is appropriate to discuss these considerations and the different forms of silicon infiltration used to produce metal-ceramic composite structures.

[0025] By way of review of the fundamental reaction-bonding process as used frequently in connection with the production of silicon carbide composite bodies, a porous mass containing at least some carbon is infiltrated with a molten infiltrant containing silicon. At least at some point during the infiltration, the silicon component of the infiltrant chemically reacts with at least a portion of the carbon in the porous mass to form silicon carbide. Typically, some infiltrant material remains in the infiltrated body, and distributed throughout. The body thus formed containing in-situ silicon carbide and residual infiltrant material is therefore a composite body. What is also typical is that the porous mass contains one or more materials that remain substantially inert under the processing conditions. These so-called"fillers" become the reinforcement component in the formed composite body.

The instant invention also encompasses an infiltration technique known as"siliconizing". This process is similar to the reaction bonding process, except that the porous mass to be infiltrated contains the one or more fillers but substantially no carbon, at least substantially none that reacts with the molten silicon. Accordingly, the formed body contains substantially no silicon carbide formed in-situ. As will be discussed in more detail to follow, the presence of carbon in the porous mass seems to assist the infiltration process in reaction-bonding. Accordingly, the siliconizing process may not be as robust as reaction-bonding. Viewed in the alternative, siliconizing may require higher processing temperatures than reaction-bonding, and may require a vacuum environment rather than an argon atmosphere.

[0026] The instant invention embraces the placement of holes, channels or other forms of engineered cavities into a preform, such as by"green machining", and infiltrating this custom shaped preform with a silicon-containing melt. The resulting silicon-containing composite body replicates the engineered cavities therein, without the need to have to machine the desired cavities in the formed composite body, or without having to machine out residual infiltrant metal that filled up the cavity during infiltration of the preform. The instant invention furthermore encompasses the fabrication of solid, unitary metal-ceramic composite structures produced as a result of gathering together a number of smaller structures, or subunits, and bonding the subunits to one another. There are a number of reasons for desiring to carry out such a procedure. For example, bonding of preform subunits can be used to produce structures whose shape is more complex than can be fabricated from the infiltration of a single porous mass or preform. Moreover, it may be impossible to perform certain machining operations on the final, unitary structure, whereas the machining might be easily performed on the individual subunits prior to assembly and bonding. Still further, it might be economically desirable from a scrap or yield perspective to minimize the number of machining operations performed on the final, unitary structure. In other words, if a RBSC part becomes scrap due to defective machining, better that the scrap part be a subunit rather than the final unitary RBSC body due to the large cost invested in a shaped RBSC body during the final processing operations, such as machining.

[0027] In one embodiment, two or more preforms are bonded together with an adhesive or cement that imparts at least strength sufficient for handling during subsequent thermal processing. The adhesive or cement contains carbon in some form amenable to being pyrolyzed to a form that is conducive to the reaction-bonding process, e. g. , elemental carbon.

Carbohydrate-based resins, as well as those based on epoxy have been found to be entirely satisfactory for providing temporary preform bonding qualities, as well as providing the carbon source for subsequent reaction-bonding during infiltration. In a preferred embodiment, the adhesive or cement composition also contains one or more filler materials, and preferably being substantially identical to any filler material making up the porous mass to be infiltrated.

[0028] The present invention is based on metal infiltration techniques involving molten metals based on silicon. Accordingly, at least one constituent of the infiltrant material comprises silicon. The infiltrant may also contain one or more other constituent (s) that may be capable of producing some desirable effect during processing or on the final character or properties of the resulting composite body. For example, the non-silicon constituent (s) may give rise to an infiltrant alloy having a lower liquidus temperature than the melting point of pure silicon. A reduced liquidus temperature might then permit the infiltration to be conducted at a lower temperature, thereby saving energy and time, as well as reducing the tendency for the infiltrant to over-infiltrate the boundaries of the preform or porous mass into the supporting materials. A non-silicon constituent infiltrated into the porous mass along with the reactive silicon constituent may produce superior properties of the resulting composite body--enhanced strength or toughness, for instance. A non-silicon constituent so infiltrated may also counterbalance the expansion of the silicon phase upon solidification, a desirable result from a number of standpoints, as will be discussed in more detail later. Elemental non-silicon constituents that fulfill one or more of the advantageous attributes include aluminum, beryllium, copper, cobalt, iron, manganese, nickel, tin, zinc, silver, gold, boron, magnesium, calcium, barium, strontium, germanium, lead, titanium, vanadium, molybdenum, chromium, yttrium and zirconium. Preferred constituents include aluminum, copper, iron, nickel, cobalt and titanium. Particularly preferred are aluminum and copper.

[0029] The atmosphere in which the infiltration of a silicon-containing alloy is conducted is usually one that is inert or mildly reducing. Accordingly, forming gas, carbon monoxide, and noble gases such as argon, helium, etc. , may be used. A vacuum environment is often preferred, however, at least from the standpoint of facilitating the reliability or robustness of infiltration. As will be discussed in more detail below, where the infiltration is excessively robust, the selection of atmosphere is one parameter that may be varied to regulate this "infiltration power".

[0030] Of course, the mass or preform to be infiltrated by the silicon-containing infiltrant must be one that is permeable to the infiltrant under the local processing conditions. Given sufficient temperature, e. g. , about 2150°C, pure silicon carbide can be infiltrated by silicon in a pressureless manner (see for example, U. S. Patent No. 3,951, 587 to Alliegro et al. ), but more typically, the porous mass contains at least some elemental or free carbon to facilitate the process. The more carbon that is present, the more silicon carbide that is produced in-situ.

[0031] While it is certainly possible to infiltrate masses containing larger amounts of carbon, what is preferred in this invention is a porous mass containing less than about 25 percent by weight carbon, and more preferably less than about 10 percent. For many of the products contemplated by the present invention, a representative selection of which are shown in some of the Examples, a particularly preferred range is about 1 percent to about 5 percent.

[0032] As briefly mentioned previously, the balance of the porous mass may comprise one or more materials that are substantially inert under the process conditions, e. g. ,"filler materials".

Candidate filler materials for use in the present invention would include the carbides such as SiC, B4C, TiC and WC; the nitrides such as Si3N4, TiN and AIN ; the borides such as SiB4, TiB2, and AlB2 ; and oxides such as A1203 and MgO. The form of the filler material may be any that can be produced, for example, particulate, fiber, platelet, flake, hollow spheres, etc.

"Fiber"includes continuous and discontinuous fiber, as well as short fiber, chopped fiber, and whiskers. The filler material bodies may range in size from submicron to several millimeters, with sizes ranging from several microns to tens of microns being common. Filler material bodies having different sizes may be blended together, for example, to increase particle packing. Fillers may also include nanotubes.

[0033] It is recognized and appreciated that many of the above-mentioned materials are not intrinsically infiltratable by silicon-containing melts under reasonable infiltration conditions.

Thus, some of these non-infiltratable materials might be candidates as containment materials, to be described in more detail later. However, by applying a coating material that is wettable and/or reactive with the silicon-containing infiltrant material, for example, carbon, at least some degree of infiltration can be achieved.

[0034] Preforms can vary greatly in their loading or theoretical density. As long as the preform (i) is capable of being wetted by the infiltrant material and (ii) contains interconnected porosity, it should be capable of being infiltrated to form the composite bodies of the present invention.

[0035] When making metal-ceramic composites using the reaction bonding process, the form of the carbon component can be significant. Specifically, some fillers such as the oxides, typically are difficult to infiltrate. Accordingly, it may be important to provide the reactable carbon in the form of a coating on the filler bodies (e. g. , particles) rather than as a mere particulate addition to the preform. One method to accomplish this is to provide the carbon to the preform in the form of a resin..

[0036] In addition to assisting in the infiltration process, another important role played by the carbonaceous resin is that of a binder. Although one can infiltrate a loose mass of filler material, the more preferred route, especially where the goal is to make an article of some particular and desired shape, is to use a self-supporting preform. Typically, a loose mass of filler material is mixed with a binder, preferably here a carbonaceous binder, and then pressed or cast or molded to a desired shape using techniques known in the art. Curing the binder then renders the formed body self-supporting.

[0037] Careful observation of the differences in infiltratability of various porous masses has enabled these differences to be exploited to advantage. Specifically, those materials that are substantially non-infiltratable under the process conditions can be used as containment materials for supporting the porous mass to be infiltrated, or for buttressing the walls of the cavity to prevent the cavity from filling up with infiltrant metal.

[0038] For example, it has been observed that reactive infiltration of an infiltrant comprising silicon into a porous mass comprising carbon occurs more robustly when the carbon is present in elemental form rather than chemically combined with other elements. Furthermore, the infiltration is more robust when the elemental carbon is present in three-dimensionally interconnected form, as opposed to discrete particle form. When the porous mass comprises a component other than elemental carbon, for example, aluminum nitride, the three- dimensionally interconnected elemental carbon phase could be present as, for example, a coating on at least some of the aluminum nitride bodies. Moreover, the infiltration is more robust when the temperature of infiltration is increased, both in terms of absolute temperature as well as in terms of the homologous temperature (e. g. , percentage or fraction of the melting temperature). Still further, infiltration is more robust when conducted under vacuum as opposed to inert gas atmosphere such as argon.

[0039] Accordingly, with these parameters in mind, it is possible to design an infiltration setup whereby a first porous mass to be infiltrated is in contact on one or more of its surfaces with a second porous mass which differs in at least one respect with regard to that which is to be infiltrated, and the liquid infiltrant can be caused to infiltrate the first porous mass but not the second porous mass.

[0040] It is well known that a porous mass comprising silicon carbide, for example, is infiltratable by silicon melts to produce a composite body. In the absence of free carbon, however, silicon carbide is reliably infiltrated by silicon (e. g. ,"siliconizing") only at temperatures well above the melting point of silicon. At temperatures just slightly above the silicon melting point, infiltration becomes rather difficult. If a metal like aluminum is alloyed with the silicon, the melting point or liquidus temperature is depressed, and the processing temperature similarly can be decreased, which further reduces the propensity for infiltration.

Under these conditions, such silicon carbide material can be used as a containment or infiltration-halting material. One desirable aspect of using silicon carbide as a containment material is that in situations where impurities or contamination is an issue (e. g. , semiconductor applications), the same source of silicon carbide can be used as a containment material as is used as a porous mass to be infiltrated without exposing the resulting silicon carbide composite body to alien or additional contaminants.

[0041] Two particularly preferred containment or"non-infilkatable"materials have now been identified, as have been the process conditions best suited to the use of each. One of the most important process parameters is the chemical composition of the infiltrant material.

[0042] Considering for now just the silicon-aluminum infiltrant system, the ability of the infiltrant to wet a porous mass of ceramic filler material, particularly SiC filler material, increases with increasing fractions of silicon metal. Thus, an infiltrant consisting essentially of pure silicon metal possesses the greatest wetting power. Here, boron nitride is an effective substance for halting continued infiltration of silicon, as it is not wetted by molten silicon. The boron nitride does not have to be dense; nor does it have to fill up the bulk volume of the cavity or channel; even a porous coating such as might be produced from the application of a boron nitride paste or paint or slip is sufficient to stop silicon infiltration when it locally reaches such boron nitride. If boron nitride cannot be used (for example, because certain sensitive applications such as semiconductor fabrication prohibit contact of the semiconductor material with any components that could be contaminated with boron), then possible substitute infitltration-halting materials might include silicon nitride or possibly even silicon carbide itself (but see the discussions of"siliconizing"above and below). Where these latter two substances are used as candidate infiltration-halting materials, it may be desirable or necessary to reduce the wetting power of the silicon infiltrant by reducing the temperature of infiltration, if possible, and/or modifying the atmosphere for infiltration, for example, by switching from vacuum to inert gas such as argon.

[0043] For silicon-based infiltrant systems that contain increasing amounts of aluminum, boron nitride becomes less effective in its ability to locally halt the infiltration, possibly because the BN is chemically attacked by the molten aluminum component of the infiltrant. At the same time however, the aluminum-containing infiltrants are not as robust in terms of wetting power as is a pure silicon infiltrant, possibly also because infiltrations with silicon- aluminum alloys typically are conducted at somewhat lower temperature than are infiltrations using pure silicon. For these Si-Al infiltrant compositions, pure silicon carbide particulate, that is, particulate that is substantially free of elemental carbon, serve as an acceptable infiltrant- halting material. As was stated earlier, the instant inventors note that pure SiC particulate may not work as an infiltration-halting material in the pure silicon infiltrant systems, because pure silicon molten metal can infiltrate a porous SiC mass under the right conditions, such as a vacuum environment and a sufficiently high temperature, which process is termed "siliconizing".

[0044] In RBSC infiltration systems, when the aluminum content in a silicon-aluminum infiltrant composition reaches the range of about 40 to 60 volume percent aluminum, it may not be necessary to have to use an infiltrant-halting material at all. Not only is the wetting power of this composition much reduced compared to that of pure silicon, but also this alloy hardly undergoes any volume change upon solidification, a phenomenon that is very useful for making components to net or near-net shape.

[0045] To prevent infiltrant material from migrating into, and possibly occluding the desired cavity, the cavity in the preform may be substantially completely filled with the infiltration- halting material. In the alternative, it is usually sufficient simply to coat the surfaces of the cavity rather than to fill the entire cavity with the infiltration-halting material. Regardless of which substance is used as the infiltration-halting material, a temporary binder material such as polyvinyl alcohol may be admixed with the halting-halting material so that the latter may be place or applied to various surfaces and remain in place during thermal processing. If the binder contains a carbon source, however, it may be important that such carbon source be removed (such as by pyrolysis) prior to the infiltration process with the silicon-containing molten metal.

[0046] Thus, the infiltration-halting material could be provided in a form where it possesses a paste consistency or viscosity. Often binders are provided in aqueous or other dissolved form, so it may be convenient or desirable to provide the infiltration-halting material in the form of a paint, slurry or slip.

[0047] Even if the temporary binder is removed prior to the infiltration step, such as during a pyrolysis step to combust a carbon source permeating the infiltration-halting material, often there is sufficient residual adhesion, however slight, to hold the infiltration-halting material, which could be in particulate form, in place during subsequent preform infiltration. The molten infiltrant permeates the porous preform but is locally stopped by the infiltration-halting material at the wall of the cavity, which is the boundary between the preform material and the infiltration-halting material. After cooling to solidify the infiltrant and to recover the formed composite body, the loosely adhered infiltration-halting material is then easily and readily removed from the formed cavity in the composite body. Sandblasting or grit blasting could be used for this removal process, but usually even this is not necessary. Often, a jet of compressed water, or even just compressed air is sufficient to knock the infiltration-halting material loose.

[0048] The following examples illustrate with still more specificity several preferred embodiments of the present invention. These examples are meant to be illustrative in nature and should not be construed as limiting the scope of the invention.

EXAMPLE 1 [0049] This example demonstrates the fabrication of a RBSC composite body containing a channel through its bulk. The channel is provided in the preform, here, an assemblage of two preform subunits bonded together, and it is filled with an infiltration-halting material to prevent its being filled with the infiltrant during the infiltration of the rest of the preform.

[0050] Two plate preforms (9.5 x 95 x 190 mm and 17 x 95 x 190 mm) of SiC particulates were made as follows: a. 240 and 500 grit SiC particles (ESK, Kempten, Germany and St. Gobain Ceramic Materials, Worcester, MA, respectively) of 63 and 17 microns size, respectively, were mixed in a ratio of 70 to 30 by weight. b. To this mix 7.5 parts by weight Krystar 300 crystalline fructose (A. E. Staley Manufacturing Co. , Decatur, IL) was added. c. To this 19.5 parts by weight de-ionized water was added. d. To this 0.5 parts by weight Tamol dispersant (Rohm & Haas Co. , Philadelphia, PA) was added. e. The mixture was mixed in a high shear mixer (Ross) and cast into rubber molds. f. The molds were placed on a vibrating table until a hard preform surface was produced. The excess water that came to the top was decanted and sponged off. g. The molds with preforms were then placed in a freezer for 3 hours. h. The molds were removed from the freezer and the preforms were removed from the molds. i. Finally, the preforms were placed on a graphite tray and fired in an inert atmosphere at around 600°C to carbonize the binder.

[0051] Five slots (6.5 x 6.5 mm) were machined in the thicker plate along the 95 mm dimension using a diamond band saw. The five slots were filled with different fillers as follows: Slot 1: 90 grit (particle size of 216 microns) seasoned (slightly surface-oxidized) SiC particles (Industrial Minerals Processing Co. , Inc. , Glen Cove, NY) Slot 2: BN paste (ZYP Coatings, Oak Ridge, TN) Slot 3: Mixture of BN paste and SiC powder Slot 4: Mixture of BN paste and Alumina powder Slot 5: Mixture of BN and alumina fiber mat [0052] Next the thin plate was bonded onto the thick plate, covering the filled slots, using a mixture of SiC and Ciba 8603 ResinFusion epoxy (Ciba Specialty Chemicals Corp. , East Lansing, MI). The bonded assembly was then placed in a vacuum furnace in contact with an 80-20 (wt%) Si-Al alloy. The chamber was evacuated to vacuum below 200 millitorr and the temperature was raised to 1350°C and held there for 1 hour. During this time, the silicon alloy melted, infiltrated the bonded preforms, reacted with the carbonized binder to form some SiC in-situ, and in general, produced a unitary reaction-bonded SiC structure. Then the furnace was cooled to room temperature. After infiltration, the 90 grit SiC could be simply poured out or vacuumed out to get an open channel number 1 (see Figure 2). The fillers in the other channels could not be easily removed, as there was at least partial infiltration of these other cavities by molten silicon alloy.

[0053] Thus, this example demonstrates the fabrication of an in-situ channel in a RBSC body without its having to be made by a machining technique. The example also demonstrated the limitations of boron nitride, which is a well-known non-infiltratable material for infiltrations in which the infiltrant is substantially pure silicon.

Example 2 [0054] In this example, a much larger (-0 13 x 400 x 560 mm) commercial component was made using the approach described in Example 1. With reference to Figure 3, this component has much longer (-6. 5 x 6.5 x 1020 mm) serpentine cooling channels. Here again, two preform plates were made, a continuous serpentine slot 31 was machined in one of them 33 from the inlet to the outlet side, it was filled with 90 grit SiC, and the second preform plate 35 was bonded on. For this component, two small access holes (not shown) were drilled in the preform over each straight portion of the cooling channel. This assembly was then infiltrated with 80: 20 Si-Al alloy. The access holes were used, in addition to the inlet and outlet holes, to assist in vacuuming out the 90 grit SiC after infiltration. The access holes were then closed off by bonding cover plugs with a thermosetting resin (e. g., epoxy) and curing the resin.

[0055] In operation, heat source 37 is mounted on one side of the cooling plate. The coolant flowing through the channel removes the heat generated by the heat source and keeps its operating temperature within limits.

INDUSTRIAL APPLICABILITY [0056] The methods and articles of the present invention should find utility in applications requiring engineered cavities, e. g., cavities having a specific size, shape and location within a composite body made by a silicon infiltration technique. Typically, the cavities will be enclosed except for entrance and exit regions; that is, a channel within the body, or"internal channel". Such channels would be useful for circulating a fluid such as a cooling medium to remove heat from the body or from a body in contact with the composite body, such as from an electrical circuit. Such channels could also be used to"pull a vacuum"from one side of the composite body to the other, for example, in a vacuum chuck application. The artisan of ordinary skill will readily think of other uses for having the instant conduits in a composite body.

[0057] Application of this technology are expected in many areas that need high conductivity, light-weight, low-CTE, fluid-flow-through components for cooling (e. g. electronics thermal management, IGBTs, semiconductor capital equipment components, aerospace components etc. ) Accordingly, among the specific articles of manufacture contemplated by the present invention are semiconductor wafer handling devices such as vacuum chucks and electrostatic chucks, air bearing housings or support frames, electronic packages and substrates.

[0058] An artisan of ordinary skill will appreciate that numerous and various modifications may be made to the invention herein described without departing from the scope or spirit of the invention as defined in the appended claims.