Composite material and method of making the composite material

A composite is formed by inserting a ceramic powder into a channel of a preform to form a ceramic powder filled preform. The ceramic powder has at least one reactive ceramic powder. The preform is a ceramic, ceramic-metal composite, metal or combination thereof that has walls that define a plurality of channels each channel having an opening at a surface of the preform. The ceramic powder filled preform is infiltrated with a molten metal to form the ceramic-metal body, which has at least one ceramic phase that is a reaction product of the reactive ceramic and molten infiltrated metal.

FIELD OF THE INVENTION

The invention relates to the formation of a macro-composite of a ceramic-metal composite within a monolithic ceramic, metal, ceramic-metal composite or combination thereof.

BACKGROUND OF THE INVENTION

Over the past several decades, many ceramic-metal composites have been developed to attempt to make materials having the advantages of ceramics (e.g., stiffness and high temperature resistance) and metals (e.g., toughness and formability) in the same material while minimizing the disadvantages of each. For example, ceramic-metal composites in which metals are reinforced with ceramic particulates of various geometries (e.g., whiskers) and ceramic fibers have been produced. Typically, such ceramic-metal composites are formed by co-sintering metal and ceramic powders, infiltrating a molten metal into a porous ceramic preform or introducing ceramic particulates into a molten metal, which is then cast.

Laminates of ceramics and metal foils are also quite common with an example being capacitors. Coatings of ceramics on metals or metals encapsulated by ceramics to reduce oxidation have been developed such as porcelain enameled cookware. Single layer laminates or coatings of ceramics and ceramic metal composites on metals have been described for making brake rotors. Likewise, tungsten carbide-cobalt has been brazed or welded on many metals to form cutting implements such as carbide tipped saw blades and drill bits.

Each of the aforementioned, however, have failed to exploit the properties of a ceramic particulate based ceramic-metal composite combined with a metal or ceramic monolithic part.

SUMMARY OF THE INVENTION

The present invention is a method of making a ceramic-metal body comprising,

a) inserting a ceramic powder into a channel of a preform to form a ceramic powder filled preform, the preform being (i) a ceramic, ceramic-metal composite, metal or combination thereof and (ii) having walls that define a plurality of channels each channel having an opening at a surface of the preform, wherein the ceramic powder is comprised of a reactive ceramic powder and the ceramic powder has a maximum particle size smaller than the smallest channel diameter of the channels, and

b) infiltrating the ceramic powder filled preform with a molten metal to form the ceramic-metal body.

The use of such a method allows for the creation of a ceramic-metal body comprised of a matrix that is a ceramic, metal, ceramic-metal or combination thereof, the matrix having walls that define channels within the matrix wherein within at least one channel of the matrix is a channel ceramic-metal composite that has a different microstructure, chemistry or combination thereof than the walls of the matrix and the channel ceramic metal composite is comprised of a channel metal and a channel ceramic phase, the channel ceramic phase being comprised of a reactive ceramic and a ceramic reaction product of the channel metal and the reactive ceramic.

The ceramic-metal body may be used in any application that metals, ceramics or ceramic-metal composites have been used such as, but not limited to, vehicular structural components, braking components, suspension components, engine components, casings, sports equipment, wheels, cables, wires, plating, gears, seals, shafts, tools and the like. The ceramic-metal body may be further joined to other bodies of differing materials to make other components.

DETAILED DESCRIPTION OF THE INVENTION

Forming the Ceramic-Metal Body

Referring to the Figures, the preform10may be a ceramic, metal, ceramic metal composite or combination thereof. For example, the outer wall20may be a metal and the inner walls30may be a ceramic or ceramic-metal composite or vice versa. In addition, some of the inner walls30may be ceramic with the remaining inner walls30being metal and/or ceramic-metal composite with any combination being suitable. Either one or all of the inner walls30or outer wall20may be a combination of metal, ceramic or ceramic-metal composite such as in a laminate structure, an example, being a coating or cladding130upon outer wall20as illustratively shown inFIG. 6. When such a coating or cladding130is present, it is preferred that the coating or cladding130is a metal. It is further preferred that such coating or cladding130facilitates or enhances the wetting and/or bonding of the channel metal160to the walls20and30of the preform10. Channel40may be blocked off on one end by plug50inserted into channel40, or barrier60affixed to the end of the preform10. The barrier60and plug50may be of any material as described for the walls20and30.

The walls20and30may be porous or essentially dense and any combination within the preform10. That is the walls20and30or portions of the walls20and30may have open porosity110and/or closed porosity120or be essentially dense. Essentially dense herein means a density of at least 99% of theoretical. Illustratively, the walls may have a porosity of 85% to no detectable porosity using standard methods to determine density or as determined using well known microscopy techniques such as metallographic techniques including quantitative stereology of a scanning electron micrograph of a polished section of the composite using the intercept method described by Underwood inQuantitative Stereology, Addison-Wesley, Reading, Mass. (1970). Preferably, the walls have a porosity less than about 75%, more preferably less than about 70%, even more preferably less than about 65% to essentially dense, preferably at most about 1% porosity, more preferably at most about 5% porosity, even more preferably at most about 10% porosity and most preferably at most about 20% porosity.

When open porosity110is present in the preform10, it is desirable, depending on application, to have such porosity to be of a size and shape such that at least some portion of the inserted ceramic powder90is able to penetrate94(penetrated inserted ceramic powder) said open porosity110. Likewise, depending on the application, it may be desirable for the inserted ceramic powder90to essentially fail to penetrate the open porosity110(essentially fail in this context means that by standard micrographic techniques less that 1% of the volume of open porosity110has been penetrated). In a preferred embodiment, at least 5 percent of the volume of any open porosity110of the walls20and30are occupied by penetrated inserted ceramic powder94. Preferably, the volume of the open porosity110that is penetrated is at least about 10%, more preferably at least about 20% and most preferably at least about 30% to desirably a volume that is essentially the same as that occupied by ceramic powder90inserted in the channel40defined by the walls20and/or30.

To reiterate, the preform10may be a ceramic, metal, ceramic metal composite or combination thereof. In a preferred embodiment, the preform10is a metal. The metal preferably is aluminum, iron, copper, nickel, zinc, magnesium, titanium, tantalum, tungsten, silicon, alloy of any one of the aforementioned or combination thereof. Preferably, the metal is iron, nickel, copper, aluminum, silicon or alloy containing a majority of one of the aforementioned or combination thereof. More preferably the metal is a ferrous based metal, nickel or alloy thereof, or copper or alloy thereof. Most preferably the metal is any combination or individually iron, iron alloy including, for example, steels, or nickel or nickel alloy.

In another preferred embodiment, preform10is a ceramic. The ceramic may be any suitable such as those known in the art and the particular ceramic may depend on the desired application. The ceramic may have any microstructure, including for example, fibers, platelets, acicular grains, isotropic grains or any combination thereof. Preferred ceramics include, for example, borides, nitrides, carbides, oxides or any mixture thereof (e.g. oxycarbides, carbonitrides etc.) or combination thereof. Particular examples of useful ceramics for the preform10include, for example, mullite, silicon carbide, boron carbide, cordierite, silicon nitride, titanium diboride, tungsten carbide, aluminum titanate, aluminum nitride, niobium titanate, aluminum oxide, magnesium oxide, silicon dioxide, silicon hexaboride and combinations thereof.

The walls20and30may be any useful shape in making the ceramic-metal body140. For example, as illustrated byFIGS. 3 and 4, the walls20and30may be cylindrical in shape such that the points of contact of each cylinder with another in a packed arrangement defines the channels40. In this embodiment, the inner cylindrical walls30A may be formed using fibers or wires or cables that are then laid within an outer wall20, which may be a tube or pipe. The inner walls30B may be formed by extrusion or by assembling a tube with flat sheets or ribbons inserted therein.

The walls20and/or30form channels40having a smallest channel diameter70within the channels40in which ceramic powder90is inserted that is greater than the maximum particle size of the inserted ceramic powder90. The smallest channel diameter70means the diameter of the largest hypothetical sphere which can be placed in one end of the channel40and pass to the other end of the channel40without getting stuck. For example, the square channels40ofFIG. 1have a smallest channel diameter70that is equal to the length of the squares edge and in this case, since the channels40have parallel walls20and30all along the channel length80, the channel diameter70is equal to the smallest channel diameter.

Generally, the smallest channel diameter of the channels that ceramic powder90is inserted into is at least 2 times larger than the maximum particle size of the inserted ceramic powder90. This ensures that the inserted ceramic powder90has a reduced possibility of creating a bridge blocking off the channel40such that channel40cannot be filled further with the ceramic powder90. It is preferred that the smallest channel diameter is at least 5 times, more preferably at least 7 times and most preferably at least 10 times larger than the maximum particle size of the ceramic powder90inserted into the channels40.

In forming the preform10, any suitable ceramic, ceramic-metal composite or metal forming method or technique may be used as well as assembling separate components and securing them together by any suitable bond such as, but not limited to, mechanical (e.g., compression fit) or chemical (e.g., fusing, welding, brazing or combinations thereof). Exemplary methods of forming the preform10include boring out the channels, extruding through a die to form the channels, folding corrugated sheets, bonding mechanically or chemically components to form the preform10.

In a preferred embodiment, the preform10is a honeycomb that may be of any external shape including the ends having something other than a flat surface (e.g., hemispherical and a raised central portion. The channels40may be of any channel length80depicted inFIG. 2. Typically the channel length80will be at least about 2 times the smallest channel diameter. Of course, the channel length80may be several times, ten times, twenty times or more than the smallest channel diameter. At some point, however, the channel length80may be so long or narrow that they may not be easily filled with inserted ceramic powder90.

The ceramic powder90inserted into channels40, may be any ceramic powder useful to make a ceramic-metal composite such as those known in the art so long as it is, generally, comprised of at least about 10% by volume of a reactive ceramic powder. The ceramic powder90may be a boride, oxide, carbide, nitride, silicide or combination thereof. Combinations include, for example, borocarbides, oxynitrides, oxycarbides and carbonitrides. Preferred ceramics include SiC, B4C, Si3N4, Al2O3, TiB2, SiB6, SiB4, AlN, ZrC, ZrB and combinations thereof. The ceramic powder90is comprised of a reactive ceramic. Reactive ceramic means that it reacts with the infiltrating molten metal during infiltration or subsequent heat treatment to form a ceramic reaction product of the reactive ceramic and infiltrated metal (channel metal160). Preferably, the ceramic powder90is comprised of, in ascending preference of at least 50%, 60%, 70%, 80%, 90%, 95% by volume of the reactive ceramic powder. In a most preferred embodiment the ceramic powder90is solely the reactive ceramic powder, which may be a combination of reactive powders.

The inserted ceramic powder90may also be mixed with a metal powder91, which, may, for example, aid in infiltrating the molten metal to form the channel ceramic metal composite150in the channel40. It is preferred that the metal powder91substantially fails to melt during the infiltrating of the molten metal. Substantially fails to melt means herein that the metal powder91at most melts at the surface of the metal powder91, which may occur due to alloying of the surface from elements in the molten metal. The amount of metal powder91mixed with the inserted ceramic powder90is generally at most about 70% by volume of the ceramic powder90. Preferably, when present, the amount of metal powder is at most about 50%, more preferably at most about 30%, even more preferably at most about 15% and most preferably at most about 10% by volume of the total amount of inserted powder90including the metal powder91.

The ceramic powder90may be inserted into the channels40by any suitable method. The ceramic powder90may be inserted dry, combined with a liquid or plastic. For example, if the ceramic powder90is dry it may be poured in the channels40and channel filling may be facilitated by shaking or application of vibration to the preform10.

Alternatively, the ceramic powder90may be inserted by mixing the ceramic powder90with a liquid, whereby the suspension is of viscosity that is low enough that it may be simply poured, injected or squirted into a channel40and the liquid medium removed, exemplary methods being described by U.S. Pat. Nos. 4,200,604 and 6,803,015. In another method, the ceramic powder90may be inserted by forming a plastic mass using suitable methods such as those known in the art to extrude ceramics by adding organic additives (e.g., dispersants, lubricants, and binders) and injecting the paste into a channel such as described in Chapter 21, ofIntroduction to the Principles of Ceramic Processing, J. Reed, John Wiley and Sons, NY, 1988.

When using a mixture of ceramic powder90and a dispersing liquid having a low viscosity, the mixture is generally fluid enough to be inserted into one end of a channel40of preform10and subsequently flow through the channel40and collect at the other end of the channel40, for example, from the mere exertion of gravity. Thus, the mixture may deposit, for example, a layer of ceramic powder90on the walls20and/or30or completely fill the channel40. Generally, the viscosity of the mixture, when using this method, is at most about 1000 centipoise (cp), more preferably the mixture has a viscosity of at most about 200 cp, even more preferably at most about 100 cp and most preferably at most about 20 cp.

The dispersing liquid may be, for example, water, any organic liquid, such as an alcohol, aliphatic, glycol, ketone, ether, aldehyde, ester, aromatic, alkene, alkyne, carboxylic acid, carboxylic acid chloride, amide, amine, nitrile, nitro, sulfide, sulfoxide, sulfone, organometallic or mixtures thereof. Preferably, the dispersing liquid is water, an aliphatic, alkene or alcohol. More preferably, the liquid is an alcohol, water or combination thereof. When an alcohol is used it is preferably methanol, propanol, ethanol or combinations thereof. Most preferably, the alcohol is propanol.

The mixture may contain other useful components, such as those known in the art of making ceramic suspensions or pastes. Examples of other useful components include dispersants, deflocculants, flocculants, plasticizers, defoamers, lubricants and preservatives, such as those described in Chapters 10-12 ofIntroduction to the Principles of Ceramic Processing, J. Reed, John Wiley and Sons, NY, 1988. A preferred binder in the mixture is one that is soluble in the dispersing liquid, but not soluble in water.

The mixture may also contain binders. Examples of binders include cellulose ethers, such as those described in Chapter 11 of Introduction to thePrinciples of Ceramic Processing, J. Reed, John Wiley and Sons, NY, NY, 1988. Preferably, the binder is a methylcellulose or ethylcellulose, such as those available from The Dow Chemical Company under the trademarks METHOCEL and ETHOCEL. Preferably, the binder dissolves in the dispersing liquid.

The ceramic powder90may fill some or all of the channels40such that there may be partially filled channels105and unfilled channels100after the ceramic powder90is inserted into the channels40. It is preferred that all of the channels40are substantially filled. Substantially filled means that the ceramic powder90, not including the void space between the particles of the ceramic powder90, occupies at least about 95% of the volume of channels40. More preferably the powder completely fills the channels40.

In another embodiment, the ceramic powder90is inserted such that it coats the walls20and/or30to some thickness, leaving a void down the channel length80of the channel40. After this a second differing ceramic powder90may be inserted in the remaining volume to make a channel40having a gradient structure from the wall20and/or30to the center of the channel40.FIG. 7illustrates one possible aforementioned gradient where ceramic powder90is comprised of three differing powders. In this illustration ceramic powder90A has the same particle size as ceramic powder90B but a different chemistry and ceramic powder90C has the same chemistry as90A, but a different particle size. Likewise, the preform10with ceramic powder90coated on walls20and/or30may be infiltrated with metal (channel metal160) and then a subsequent ceramic powder inserted in the channel40may be coated onto the channel remaining after the first metal has infiltrated. This second inserted ceramic powder may be infiltrated. This sequence of steps may be repeated as often as desired and preferably until the channel40are completely filled having a gradient structure across the channel diameter70.

In a similar manner, a channel40may be partially filled with a ceramic powder90, and then filled further with another ceramic powder90having a different chemistry, particle packing or particle size to create a gradient structure down the channel length80of the channel40. Returning toFIG. 7, ceramic powder90A may first be inserted into channel40and then the other powder90A, B and C inserted and infiltrated as described in the previous paragraph to create a gradient structure along channel length80and along the channel diameter along a portion of channel40. Any combinations of filling the channels40of preform10may be utilized as desired. Examples include, but in no way limit the potential combinations, are where (1) at least one channel40has a different ceramic powder90than that inserted into another channel40, (2) the ceramic powder90inserted into at least one channel40differs within the channel40either along the channel length80of the channel40or across the channel diameter70of the channel40. The ceramic powder90differs when at least one characteristic of the ceramic powder90varies such as the composition, chemistry, packing, particle size or combination thereof. Differs, herein, means that a characteristic, such as one of the aforementioned, is statistically different by known standard methods to determine such characteristics. It is also understood that differs refers not to individual microstructural features such as a grain of a ceramic within a metal-ceramic composite, but, generally, to regions that are a volume of at least about 10 times greater than the average grain size of the ceramic grains within the channel ceramic-metal composite150. Such differences may be determined by known microscopic methods such as on polish sections to determine the grain size of the ceramic grains, packing of the ceramic particles, chemistry and the like.

In a preferred embodiment, within at least one channel40, the ceramic powder90varies in composition, packing or combination thereof.

When using a liquid or polymeric medium to suspend the ceramic powder90, the suspending medium may be removed by any suitable method. For example when the medium is a liquid, such as water or alcohol, the liquid may be removed by drying in air, drying by application of heat or vacuum, or by removing it by blocking the channel40ends on one end of the preform10with a porous medium that removes the dispersing liquid by capillary action. An example of such a porous medium is plaster of Paris, such as that used in slip casting ceramics. To remove any organic liquids that are not removed by evaporative drying or capillary action, the preform10with the inserted ceramic powder90may be subjected to any suitable process including well known processes such as heating under a suitable atmosphere to effect the removal of such additives.

Referring toFIG. 8, after the ceramic powder90is inserted into the channels40of preform10, molten metal is infiltrated into the ceramic powder90such that a channel ceramic metal composite150is formed in the channel40that is bonded to the walls20and/or30. The infiltration of the molten metal (channel metal160) may be done by any suitable method such as those known in the art. Exemplary methods include those described by U.S. Pat. Nos. 5,007,475; 5,020,584; 5,298,469; 5,521,016; and 5,775,403.

After the metal has been infiltrated, the body140may be further heat treated to react the infiltrated metal (channel metal160) with the reactive ceramic. Exemplary methods of subsequent heat treatments are described in U.S. Pat. Nos. 5,298,468 and 5,521,016.

The Ceramic-Metal Body

The method of the invention is able to form a ceramic-metal body140comprised of a matrix that is a ceramic, metal, ceramic-metal or combination thereof, the matrix having walls20and30that define channels40within the matrix wherein within at least one channel40of the matrix is a channel ceramic-metal composite150that differs from the walls20and30of the matrix and the channel ceramic metal composite150is comprised of a channel metal160and a channel ceramic phase170the channel ceramic phase170being comprised of a reactive ceramic and a ceramic reaction product of the channel metal160and the reactive ceramic. The reactive ceramic is as described above for the reactive ceramic powder

Generally, at least about 10% by volume of the reactive ceramic is reacted with the channel metal160to form the ceramic reaction product. In ascending preference, the volume of the reactive ceramic that is reacted is at least about 15%, 20%, 30%, 40%, 50%, 60%, 70% and 80%. In a preferred embodiment, the degree of reaction of reactive ceramic is different within at least one channel40or between channels40. For example, the particle size or chemistry (e.g., the reactive powder may be treated, for example, by coating with a metal or other ceramic etc. to slow or speed the reactivity of the powder) of a reactive ceramic powder may be different within each channel40resulting in differing reactivity. Likewise, within a channel40, the volume of the reactive powder that has been reacted may vary along the channel length80or channel diameter70of channel40.

In a another preferred embodiment, the ceramic-metal body140has, along the channel length80of at least one channel40, a variation of property, structure, chemistry or combination thereof of the channel ceramic-metal composite150. In ascending preference, at least 15%, 20%, 30%, 40%, 50%, 60%, 70% and 80% of the channels40have a varying channel ceramic-metal composite150. In a most preferred embodiment, all of the channels40have a varying channel ceramic-metal composite150. In a like manner, the channel ceramic-metal composite150varies across a channel diameter70of a channel or channel40.

In a preferred embodiment, the channel metal160is selected from aluminum, zirconium, titanium, copper, silicon, magnesium, alloys of each of the aforementioned and mixtures thereof. Likewise it is preferred that the reactive ceramic is boron carbide and the channel metal160is comprised of aluminum and the ceramic reaction product is comprised of at least one ceramic selected from

Preferably, the ceramic reaction product is comprised of at least two of these ceramics. It is also preferred for these preferred embodiments that all of the channels40have the described channel metal or metals160and channel ceramic phase170.

A further illustration of the usefulness of the present invention is where a portion of the body140is subject to tensile or shearing stress such as the inner hub of a brake rotor, the channels40there may desirably have a high toughness channel ceramic metal composite150(e.g., a ceramic powder mixed with metal powder giving a greater toughness channel ceramic-metal composite150), whereas the channels40where the brake rotor contacts a brake pad may desirably have a more wear resistant channel ceramic metal composite150(e.g., one that is almost all ceramic, which may be derived by using solely reactive ceramic powder). Likewise, the use of an insert of the invention's body140may be attached to a metal brake rotor. Illustratively, such an insert can have a tougher channel ceramic-metal composite150, that is with substantial amounts of metal such as greater than 50% that is mounted to the metal brake rotor, for example, by a mechanical fastener with the opposite end that contacts the brake pad being almost all ceramic for improved wear properties as just described above.

EXAMPLES

A 2 inch by 2 inch wide and 1 inch deep mullite honeycomb having 2×2 mm wide channels and wall porosity of 60% was filled with two slurries with alternating channels being filled by each slurry. The mullite honeycomb was produced by The Dow Chemical Company in a manner as shown in U.S. Pat. Publication 2005/0115214. The first slurry contained 20% by volume ESK 1500 B4C powder (TETRABOR ESK 1500, ESK Ceramics GMBH & Co., Kempten, Germany) in 7 pH water. The second slurry contained 15% by volume of a mixture containing by volume 90% TiB2(HCT 30D, available from General Electric Company, GE Advanced Materials Unit, Wilton, Conn.) and 10% B4C (ESK 1500). The average particle size of the B4C was 3-5 microns and average size of the TiB2was 14 microns. The slurries were placed into selective channels of the mullite honeycomb (checkerboard) using a thin plastic tube and eye-dropper. The channel filled honeycomb was dried for 24 hours at 80° C. The dried filled honeycomb was placed into a steel die and heated in air to about 400° C. The preheated part was transferred to a pressure casting unit (THT Presses, Inc., Dayton, Ohio) and molten aluminum was injected into the part for about 5-10 seconds. The liquid metal easily penetrated all openings producing dense walls and channels. The ceramic-metal part consisted of two types of ceramic-metal channels isolated by the continuous network of Al-Mullite composite. The first set of channels had a ceramic metal composite with aluminum metal, boron carbide and ceramic reaction phases AlB2and a solid solution phase Al(3-4)BC and the other set of channels had a ceramic-metal composite containing Al, TiB2, B4C, and ceramic reaction phase AlB2.

The same process was applied as in Example 1 except that the channels were filled in 5 layers from bottom to top with varying sizes of reactive B4C particles. The varying sizes were made by mixing various ratios of two grades of B4C powders (TETRABOR F1200 and F180, ESK Ceramics GMBH & Co., Kempten, Germany). The powders were inserted dry into the channels and the entire honeycomb was tapped and shook for about 10 seconds to increase the particle packing after each layer was introduced. The thickness of each layer was about 2 mm. The powder composition of the layers starting from one end were: (I) 100% F1200, (II) 75% F1200:25% F-180, (III) 50% F1200:50% F180, (IV) 25% F1200: 75% F180 and (V) 100% F180. After infiltration, the ceramic metal body was heat-treated at 700° C. for 10 hours. The ceramic metal body had a graded structure varying in Vickers hardness from about 1100 Kg.mm2on one side to about 400 kg/mm2on the opposite side.