WO1991017275A1 - Composites a matrice metallique poreuse et procedes de fabrication - Google Patents

Composites a matrice metallique poreuse et procedes de fabrication Download PDF

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Publication number
WO1991017275A1
WO1991017275A1 PCT/US1991/003160 US9103160W WO9117275A1 WO 1991017275 A1 WO1991017275 A1 WO 1991017275A1 US 9103160 W US9103160 W US 9103160W WO 9117275 A1 WO9117275 A1 WO 9117275A1
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WO
WIPO (PCT)
Prior art keywords
metal
matrix
filler
preform
infiltration
Prior art date
Application number
PCT/US1991/003160
Other languages
English (en)
Inventor
Marc Stevens Newkirk
Original Assignee
Lanxide Technology Company, Lp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Lanxide Technology Company, Lp filed Critical Lanxide Technology Company, Lp
Priority to JP91510410A priority Critical patent/JPH05507122A/ja
Publication of WO1991017275A1 publication Critical patent/WO1991017275A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/009—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone characterised by the material treated
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
    • C04B41/50—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with inorganic materials
    • C04B41/51—Metallising, e.g. infiltration of sintered ceramic preforms with molten metal
    • C04B41/515—Other specific metals
    • C04B41/5155—Aluminium
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
    • C04B41/81—Coating or impregnation
    • C04B41/85—Coating or impregnation with inorganic materials
    • C04B41/88—Metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/10—Alloys containing non-metals
    • C22C1/1036—Alloys containing non-metals starting from a melt
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/10—Alloys containing non-metals
    • C22C1/1036—Alloys containing non-metals starting from a melt
    • C22C1/1057—Reactive infiltration
    • C22C1/1063—Gas reaction, e.g. lanxide
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00612—Uses not provided for elsewhere in C04B2111/00 as one or more layers of a layered structure
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00905—Uses not provided for elsewhere in C04B2111/00 as preforms
    • C04B2111/00913—Uses not provided for elsewhere in C04B2111/00 as preforms as ceramic preforms for the fabrication of metal matrix comp, e.g. cermets
    • C04B2111/00931—Coated or infiltrated preforms, e.g. with molten metal

Definitions

  • the present invention relates to a novel process for forming porous metal matrix composite bodies.
  • an infiltration enhancer and/or an infiltration enhancer precursor and/or an infiltrating atmosphere are in communication with a filler material or a preform, at least at some point during the process, which permits molten matrix metal to spontaneously infiltrate the filler material or preform.
  • Such spontaneous infiltration occurs without the requirement for the application of pressure or vacuum.
  • the amount of matrix metal provided is insufficient to embed substantially completely the filler material or preform.
  • Composite products comprising a metal matrix and a strengthening or reinforcing phase such as ceramic particulates, whiskers, fibers or the like, show great promise for a variety of applications because they combine some of the stiffness and wear resistance of the reinforcing phase with the ductility and toughness of the metal matrix.
  • a metal matrix composite will show an improvement in such properties as strength, stiffness, contact wear resistance, coefficient of thermal expansion (C.T.E.), density, thermal conductivity and elevated temperature strength retention relative to the matrix metal in monolithic form, but the degree to which any given property may be improved depends largely on the specific constituents, their volume or weight fraction, and how they are processed in forming the composite. In some instances, the composite also may be lighter in weight than the matrix metal per se.
  • Aluminum matrix composites reinforced with ceramics such as silicon carbide in particulate, platelet, or whisker form, for example, are of interest because of their higher specific stiffness (e.g., elastic modulus over density), wear resistance, thermal conductivity, low coefficient of thermal expansion (C.T.E.) and high temperature strength and/or specific strength (e.g., strength over density) relative to aluminum.
  • Various metallurgical processes have been described for the fabrication of aluminum matrix composites, including methods based on powder metallurgy techniques and liquid-metal infiltration techniques which make use of pressure casting, vacuum casting, stirring, and wetting agents.
  • the metal in the form of a powder and the reinforcing material in the form of a powder, whiskers, chopped fibers, etc. are admixed and then either cold-pressed and sintered, or hot-pressed.
  • the maximum ceramic volume fraction in silicon carbide reinforced aluminum matrix composites produced by this method has been reported to be about 25 volume percent in the case of whiskers, and about 40 volume percent in the case of particulates.
  • U.S. Patent No. 3,970,136 granted July 20, 1976, to J. C. Cannell et al., describes a process for forming a metal matrix composite incorporating a fibrous reinforcement, e.g. silicon carbide or alumina whiskers, having a predetermined pattern of fiber orientation.
  • the composite is made by placing parallel mats or felts of coplanar fibers in a mold with a reservoir of molten matrix metal, e.g., aluminum, between at least some of the mats, and applying pressure to force molten metal to penetrate the mats and surround the oriented fibers.
  • Molten metal may be poured onto the stack of mats while being forced under pressure to flow between the mats.
  • the aforesaid pressure- infiltration method allows for only a relatively low reinforcement to matrix volume fraction to be achieved because of the difficulty inherent in infiltrating a large mat volume. Still further, molds are required to contain the molten metal under pressure, which adds to the expense of the process. Finally, the aforesaid process, limited to infiltrating aligned particles or fibers, is not directed to formation of aluminum metal matrix composites reinforced with materials in the form of randomly oriented particles, whiskers or fibers.
  • aluminum does not readily wet alumina, thereby making it difficult to form a coherent product.
  • Various solutions to this problem have been suggested.
  • One such approach is to coat the alumina with a metal (e.g., nickel or tungsten), which is then hot-pressed along with the aluminum.
  • the aluminum is alloyed with lithium, and the alumina may be coated with silica.
  • these composites exhibit variations in properties, or the coatings can degrade the filler, or the matrix contains lithium which can affect the matrix properties.
  • 115,742 describes making aluminum-alumina composites, especially useful as electrolytic cell components, by filling the voids of a preformed alumina matrix with molten aluminum.
  • the application emphasizes the non-wettability of alumina by aluminum, and therefore various techniques are employed to wet the alumina throughout the preform.
  • the alumina is coated with a wetting agent of a diboride of titanium, zirconium, hafnium, or niobium, or with a metal, i.e., lithium, magnesium, calcium, titanium, chromium, iron, cobalt, nickel, zirconium, or hafnium.
  • Inert atmospheres, such as argon are employed to facilitate wetting.
  • This reference also shows applying pressure to cause molten aluminum to penetrate an uncoated matrix.
  • infiltration is accomplished by evacuating the pores and then applying pressure to the molten aluminum in an inert atmosphere, e.g., argon.
  • the preform can be infiltrated by vapor-phase aluminum deposition to wet the surface prior to filling the voids by infiltration with molten aluminum.
  • heat treatment e.g., at 1400 to 1800 ⁇ C, in either a vacuum or in argon is required. Otherwise, either exposure of the pressure infiltrated material to gas or removal of the infiltration pressure will cause loss of aluminum from the body.
  • wetting agents to effect infiltration of an alumina component in an electrolytic cell with molten metal is also shown in European Patent Application Publication No. 94353.
  • This publication describes production of aluminum by electrowinning with a cell having a cathodic current feeder as a cell liner or substrate.
  • a thin coating of a mixture of a wetting agent and solubility suppressor is applied to the alumina substrate prior to start-up of the cell or while immersed in the molten aluminum produced by the electrolytic process.
  • Wetting agents disclosed are titanium, zirconium, hafnium, silicon, magnesium, vanadium, chromium, niobium, or calcium, and titanium is stated as the preferred agent.
  • U.S. Patent No. 3,864,154, granted February 4, 1975, to G. E. Gazza et al. also shows the use of vacuum to achieve infiltration.
  • This patent describes loading a cold-pressed compact of AIB* ⁇ powder onto a bed of cold-pressed aluminum powder. Additional aluminum was then positioned on top of the A1B 12 powder compact. The crucible, loaded with the A1B 12 compact "sandwiched" between the layers of aluminum powder, was placed in a vacuum furnace. The furnace was evacuated to approximately 10 " ° torr to permit outgassing. The temperature was subsequently raised to 1100 ⁇ C and maintained for a period of 3 hours. At these conditions, the molten aluminum penetrated the porous A1B 12 compact.
  • U.S. Patent No. 3,364,976, granted January 23, 1968 to John N. Reding et al. discloses the concept of creating a self-generated vacuum in a body to enhance penetration of a molten metal into the body. Specifically, it is disclosed that a body, e.g., a graphite mold, a steel mold, or a porous refractory material, is entirely submerged in a molten metal. In the case of a mold, the mold cavity, which is filled with a gas reactive with the metal, communicates with the externally located molten metal through at least one orifice in the mold.
  • a body e.g., a graphite mold, a steel mold, or a porous refractory material
  • Molds must first be machined into a particular shape; then finished, machined to produce an acceptable casting surface on the mold; then assembled prior to their use; then disassembled after their use to remove the cast piece therefrom; and thereafter reclaim the mold, which most likely would include refinishing surfaces of the mold or discarding the mold if it is no longer acceptable for use. Machining of a mold into a complex shape can be very costly and time-consuming. Moreover, removal of a formed piece from a complex-shaped mold can also be difficult (i.e., cast pieces having a complex shape could be broken when removed from the mold).
  • the present invention satisfies these needs by providing a spontaneous infiltration mechanism for infiltrating a material (e.g., a ceramic material), which can be formed into a preform, with molten matrix metal (e.g., aluminum) in the presence of an infiltrating atmosphere (e.g., nitrogen) under normal atmospheric pressures so long as an infiltration enhancer precursor and/or infiltration enhancer is present at least at some point during the process.
  • a spontaneous infiltration mechanism for infiltrating a material e.g., a ceramic material
  • molten matrix metal e.g., aluminum
  • an infiltrating atmosphere e.g., nitrogen
  • a metal matrix composite is produced by infiltrating a permeable mass of filler material (e.g., a ceramic or a ceramic-coated material) with molten aluminum containing at least about 1 percent by weight magnesium, and preferably at least about 3 percent by weight magnesium. Infiltration occurs spontaneously without the application of external pressure or vacuum.
  • a supply of the molten metal alloy is contacted with the mass of filler material at a temperature of at least about 675 ⁇ C in the presence of a gas comprising from about 10 to 100 percent, and preferably at least about 50 percent, nitrogen by volume, and a remainder of the gas, if any, being a nonoxidizing gas, e.g., argon.
  • the molten aluminum alloy infiltrates the ceramic mass under normal atmospheric pressures to form an aluminum (or aluminum alloy) matrix composite.
  • the temperature is lowered to solidify the alloy, thereby forming a solid metal matrix structure that embeds the reinforcing filler material.
  • the supply of molten alloy delivered will be sufficient to permit the infiltration to proceed essentially to the boundaries of the mass of filler material.
  • the amount of filler material in the aluminum matrix composites produced according to the White et al . invention may be exceedingly high. In this respect, filler to alloy volumetric ratios of greater than 1:1 may be achieved.
  • aluminum nitride can form as a discontinuous phi. dispersed throughout the aluminum matrix.
  • the amount of nitride in the aluminum matrix may vary depending on such factors as temperature, alloy composition, gas composition and filler material. Thus, by controlling one or more such factors in the system, it is possible to tailor certain properties of the composite. For some end use applications, however, it may be desirable that the composite contain little or substantially no aluminum nitride.
  • the White et al . invention allows the choice of a balance between infiltration kinetics and nitride formation.
  • a barrier means e.g., particulate titanium diboride or a graphite material such as a flexible graphite foil product sold by Union Carbide under the trade name Grafoil ®
  • the barrier means is used to inhibit, prevent, or terminate infiltration of the molten alloy, thereby providing net, or near net, shapes in the resultant metal matrix composite.
  • the formed metal matrix composite bodies have an outer shape which substantially corresponds to the inner shape of the barrier means.
  • the first source of molten matrix alloy begins to infiltrate the mass of filler material under normal atmospheric pressures and thus begins the formation of a metal matrix composite.
  • the first source of molten matrix metal alloy is consumed during its infiltration into the mass of filler material and, if desired, can be replenished, preferably by a continuous means, from the reservoir of molten matrix metal as the spontaneous infiltration continues.
  • the temperature is lowered to solidify the alloy, thereby forming a solid metal matrix structure that embeds the reinforcing filler material.
  • a reservoir of metal is simply one embodiment of the invention described in this patent application and it is not necessary to combine the reservoir embodiment with each of the alternate embodiments of the invention disclosed therein, some of which could also be beneficial to use in combination with the present invention.
  • the reservoir of metal can be present in an amount such that it provides for a sufficient amount of metal to infiltrate the permeable mass of filler material to a predetermined extent.
  • an optional barrier means can contact the permeable mass of filler on at least one side thereof to define a surface boundary.
  • the supply of molten matrix alloy delivered should be at least sufficient to permit spontaneous infiltration to proceed essentially to the boundaries (e.g., barriers) of the permeable mass of filler material
  • the amount of alloy present in the reservoir could exceed such sufficient amount so that not only will there be a sufficient amount of alloy for complete infiltration, but excess molten metal alloy could remain and be attached to the metal matrix composite body.
  • the resulting body will be a complex composite body (e.g., a acrocomposite), wherein an infiltrated ceramic body having a metal matrix therein will be directly bonded to excess metal remaining in the reservoir.
  • a porous metal matrix composite body is produced by spontaneously infiltrating a permeable mass of filler material or a preform with a molten matrix metal.
  • an infiltration enhancer and/or an infiltration enhancer precursor and/or an infiltrating atmosphere are in communication with the filler material or preform, at least at some point during the process, which permits molten matrix metal to spontaneously infiltrate the filler material or preform.
  • the amount of matrix metal which infiltrates the filler material or preform is insufficient to embed substantially completely the filler material or preform.
  • a precursor to an infiltration enhancer may be supplied to at least one of a filler material or preform and/or a matrix metal and/or an infiltrating atmosphere.
  • the supplied infiltration enhancer precursor may thereafter react with at least one of the filler material or preform and/or the matrix metal and/or the infiltrating atmosphere to produce infiltration enhancer in at least a portion of, or on, the filler material or preform.
  • infiltration enhancer should be in contact with at least a portion of the filler material or preform.
  • an infiltration enhancer may be supplied directly to at least one of the preform and/or matrix metal and/or infiltrating atmosphere. Ultimately, at least during the spontaneous infiltration, the infiltration enhancer should be in contact with at least a portion of the filler material or preform.
  • This application discusses various examples of matrix metals, which at some point during the formation of a metal matrix composite, are contacted with an infiltration enhancer precursor, in the presence of an infiltrating atmosphere.
  • various references will be made to particular matrix metal/infiltration enhancer precursor/infiltrating atmosphere systems which exhibit spontaneous infiltration.
  • many other matrix metal/infiltration enhancer precursor/infiltrating atmosphere systems other than those discussed in this application may behave in a manner similar to the systems discussed above herein. Specifically, spontaneous infiltration behavior has been observed in the aluminum/magnesium/nitrogen system; the aluminum/strontium/nitrogen system; the aluminum/zinc/oxygen system; and the aluminum/calcium/nitrogen system.
  • the matrix metal and/or preform or filler material communicate with an infiltrating atmosphere for substantially all of the process.
  • the preform or filler material will be spontaneously infiltrated by molten matrix metal, and the extent or rate of spontaneous infiltration and formation of metal matrix composite will vary with a given set of processing conditions including, for example, the concentration of infiltration enhancer precursor provided to the system (e.g., in the molten matrix alloy and/or in the filler material or preform and/or in the infiltrating atmosphere), the size and/or composition of the filler material, the size and/or composition of particles in the preform, the available porosity for infiltration into the preform or filler material, the time permitted for infiltration to occur, and/or the temperature at which infiltration occurs.
  • the physical and mechanical properties of the formed porous metal matrix composite bodies may be engineered to any particular application or need. For example, by providing a predetermined amount of filler material and by selecting the amount of matrix metal provided for infiltration, the amount of porosity within a formed metal matrix composite body can be controlled. Moreover, by varying the amount and/or composition of matrix metal provided to, e.g., one portion of a filler material or preform relative to another portion of the filler material or preform, the porosity in the metal matrix composite body may be tailored to suit a specific application.
  • a formed metal matrix composite body by subjecting a formed metal matrix composite body to a post treatment process (e.g., heat treatment, etc.) the mechanical and/or physical properties may be further engineered to meet any particular application or need. Still further, by controlling the processing conditions during the formation of a metal matrix composite the, e.g., nitrogen content, etc., of the formed metal matrix composite may be tailored to meet a wide range of industrial applications.
  • a post treatment process e.g., heat treatment, etc.
  • the physical and/or mechanical properties of the formed porous metal matrix composite can be controlled or engineered to meet any number of industrial needs.
  • the mechanical and/or physical properties e.g., density, elastic and/or specific modulus, strength and/or specific strength, etc.
  • the mechanical and/or physical properties of a formed porous metal matrix composite body may be tailored depending on the loading of the filler material in the loose mass or in the preform and the amount of matrix metal provided for infiltration.
  • a porous metal matrix composite body can be achieved by providing, for example, a loose mass or preform comprising a mixture of filler particles of varying sizes and/or shapes to achieve a relatively high loading, due to enhanced packing of the filler material, in combination with providing an amount of matrix metal which is insufficient to embed substantially completely the filler material or preform.
  • the density of a porous metal matrix composite body can be further reduced by providing a porous filler material or porous preform (e.g., a loosely packed filler material or preform and/or a hollow filler material) in combination with an amount of matrix metal which is sufficient only to coat the filler material.
  • porous metal matrix composite can be engineered to contain a de red combination of properties.
  • a metal matrix composite body may be formed by partially, or substantially completely, infiltrating a permeable mass of filler material or preform, and subsequently, leaching out at least a portion of the matrix metal from the composite body by, e.g., thermal etching, chemical etching, etc., to produce a porous metal matrix composite body.
  • Porous metal matrix composite bodies formed according to the method of the present invention may be tailored to suit a wide number of industrial applications.
  • the composition of the matrix metal and/or filler material, the size and/or shape of the metal matrix composite body, the composition of the filler material, the porosity within the metal matrix body, etc. porous metal matrix composite bodies may be tailored for use in such applications as thermal insulation materials, filters, strainers, etc.
  • a porous metal matrix composite body may be used as a preform for forming a metal matrix composite body by a spontaneous infiltration technique, or by an alternate metal matrix formation technique.
  • porous metal matrix composite bodies formed by the method of the present invention may be tailored to serve a wide variety of uses. Definitions
  • Aluminum as used herein, means and includes essentially pure metal (e.g., a relatively pure, commercially available unalloyed aluminum) or other grades of metal and metal alloys such as the commercially available metals having impurities and/or alloying constituents such as iron, silicon, copper, magnesium, manganese, chromium, zinc, etc., therein.
  • An aluminum alloy for purposes of this definition is an alloy or intermetallic compound in which aluminum is the major constituent.
  • "Balance Non-Oxidizing Gas” means that any gas present in addition to the primary gas comprising the infiltrating atmosphere, is either an inert gas or a reducing gas which is substantially non-reactive with the matrix metal under the process conditions. Any oxidizing gas which may be present as an impurity in the gas(es) used should be insufficient to oxidize the matrix metal to any substantial extent under the process conditions.
  • Barrier or “barrier means”, as used herein, means any suitable means which interferes, inhibits, prevents or terminates the migration, movement, or the like, of molten matrix metal beyond a surface boundary of a permeable mass of filler material or preform, where such surface boundary is defined by said barrier means.
  • Suitable barrier means may be any such material, compound, element, composition, or the like, which, under the process conditions, maintains some integrity and is not substantially volatile (i.e., the barrier material does not volatilize to such an extent that it is rendered non-functional as a barrier).
  • suitable “barrier means” includes materials which are substantially non-wettable by the migrating molten matrix metal under the process conditions employed.
  • a barrier of this type appears to exhibit substantially little or no affinity for the molten matrix metal, and movement beyond the defined surface boundary of the mass of filler material or preform is prevented or inhibited by the barrier means.
  • the barrier reduces any final machining or grinding that may be required and defines at least a portion of the surface of the resulting metal matrix composite product.
  • the barrier may in certain cases be permeable or porous, or rendered permeable by, for example, drilling holes or puncturing the barrier, to permit gas to contact the molten matrix metal, etc.
  • Carcass or “Carcass of Matrix Metal”, as used herein, refers to any of the original body of matrix metal remaining which has not been 11775 consumed during formation of the metal matrix composite body, and typically, if allowed to cool, remains in at least partial contact with the metal matrix composite body which has been formed. It should be understood that the carcass may also include a second or foreign metal therein.
  • Fillers is intended to include either single constituents or mixtures of constituents which are substantially non ⁇ reactive with and/or of limited solubility in the matrix metal and may be single or multi-phase. Fillers may be provided in a wide variety of forms and sizes, such as powders, flakes, platelets, microspheres, whiskers, bubbles, etc., and may be either dense or porous. "Filler” may also include ceramic fillers, such as alumina or silicon carbide as fibers, chopped fibers, particulates, whiskers, bubbles, spheres, fiber mats, or the like, and ceramic-coated fillers such as carbon fibers coated with alumina or silicon carbide to protect the carbon from attack, for example, by a molten aluminum parent metal. Fillers may also include metals.
  • Hot-Topping refers to the placement of a substance on one end (the “topping" end) of an at least partially formed metal matrix composite which reacts exothermally with at least one of the matrix metal and/or filler material and/or with another material supplied to the topping end. This exothermic reaction should provide sufficient heat to maintain the matrix metal at the topping end in a molten state while the balance of the matrix metal in the composite cools to solidification temperature.
  • Infiltrating Atmosphere means that atmosphere which is present which interacts with the matrix metal and/or preform (or filler material) and/or infiltration enhancer precursor and/or infiltration enhancer and permits or enhances spontaneous infiltration of the matrix metal to occur.
  • Infiltration Enhancer means a material which promotes or assists in the spontaneous infiltration of a matrix metal into a filler material or preform.
  • An infiltration enhancer may be formed from, for example, a reaction of an infiltration enhancer precursor with an infiltrating atmosphere to form (1) a gaseous species and/or (2) a reaction product of the infiltration enhancer precursor and the infiltrating atmosphere and/or (3) a reaction product of the infiltration enhancer precursor and the filler material or preform.
  • the infiltration enhancer may be supplied directly to -at least one of the preform, and/or matrix metal, and/or infiltrating atmosphere and function in a substantially similar manner to an infiltration enhancer which has formed as a reaction between an infiltration enhancer precursor and another species.
  • the infiltration enhancer should be located in at least a portion of the filler material or preform to achieve spontaneous infiltration.
  • Infiltration Enhancer Precursor or "Precursor to the Infiltration Enhancer”, as used herein, means a material which when used in combination with the matrix metal, preform and/or infiltrating atmosphere forms an infiltration enhancer which induces or assists the matrix metal to spontaneously infiltrate the filler material or preform.
  • the precursor to the infiltration enhancer it appears as though it may be necessary for the precursor to the infiltration enhancer to be capable of being positioned, located or transportable to a location which permits the infiltration enhancer precursor to interact with the infiltrating atmosphere and/or the preform or filler material and/or matrix metal.
  • the infiltration enhancer precursor in some matrix metal/infiltration enhancer precursor/infiltrating atmosphere systems, it is desirable for the infiltration enhancer precursor to volatilize at, near, or in some cases, even somewhat above the temperature at which the matrix metal becomes molten.
  • volatilization may lead to: (1) a reaction of the infiltration enhancer precursor with the infiltrating atmosphere to form a gaseous species which enhances wetting of the filler material or preform by the matrix metal; and/or (2) a reaction of the infiltration enhancer precursor with the infiltrating atmosphere to form a solid, liquid or gaseous infiltration enhancer in at least a portion of the filler material or preform which enhances wetting; and/or (3) a reaction of the infiltration enhancer precursor within the filler material or preform which forms a solid, liquid or gaseous infiltration enhancer in at least a portion of the filler material or preform which enhances wetting.
  • Microx Metal or “Matrix Metal Alloy”, as used herein, means that metal which is utilized to form a metal matrix composite (e.g., before infiltration) and/or that metal which is intermingled with a filler material to form a metal matrix composite body (e.g., after infiltration).
  • a specified metal is mentioned as the matrix metal, it should be understood that such matrix metal includes that metal as an essentially pure metal, a commercially available metal having impurities and/or alloying constituents therein, an intermetallic compound or an alloy in which that metal -. the major or predominant constituent.
  • Microx Metal/Infiltration Enhancer Precursor/Infiltrating Atmosphere System or “Spontaneous System”, as used herein, refers to that combination of materials which exhibit spontaneous infiltration into a preform or filler material. It should be understood that whenever a "/" appears between an exemplary matrix metal, infiltration enhancer precursor and infiltrating atmosphere that the "/" is used to designate a system or combination of materials which, when combined in a particular manner, exhibits spontaneous infiltration into a preform or filler material .
  • Metal Matrix Composite or “MMC”. as used herein, means a material comprising a two- or three-di ensionally interconnected alloy or matrix metal which has embedded a preform or filler material.
  • the matrix metal may include various alloying elements to provide specifically desired mechanical and physical properties in the resulting composite.
  • a Metal "Different" from the Matrix Metal means a metal which does not contain, as a primary constituent, the same metal as the matrix metal (e.g., if the primary constituent of the matrix metal is aluminum, the "different" metal could have a primary constituent of, for example, nickel).
  • Nonreactive Vessel for Housing Matrix Metal means any vessel which can house or contain a filler material (or preform) and/or molten matrix metal under the process conditions and not react with the matrix and/or the infiltrating atmosphere and/or infiltration enhancer precursor and/or a filler material or preform in a manner which would be significantly detrimental to the spontaneous infiltration mechanism.
  • the nonreactive vessel may be disposable and removable after the spontaneous infiltration of the molten matrix metal has been completed.
  • Preform or “Permeable Preform”, as used herein, means a porous mass of filler or filler material which is manufactured with at least one surface boundary which essentially defines a boundary for infiltrating matrix metal, such mass retaining sufficient shape integrity and green strength to provide dimensional fidelity prior to being infiltrated by the matrix metal.
  • the mass should be sufficiently porous to accommodate spontaneous infiltration of the matrix metal thereinto.
  • a preform typically comprises a bonded array or arrangement of filler, either homogeneous or heterogeneous, and may be comprised of any suitable material (e.g., ceramic and/or metal particulates, powders, fibers, whiskers, etc., and any combination thereof).
  • a preform may exist either singularly or as an assemblage.
  • Reservoir means a separate body of matrix metal positioned relative to a mass of filler or a preform so that, when the metal is molten, it may flow to replenish, or in some cases to initially provide and subsequently replenish, that portion, segment or source of matrix metal which is in contact with the filler or preform.
  • “Spontaneous Infiltration” means the infiltration of matrix metal into the permeable mass of filler or preform occurs without requirement for the application of pressure or vacuum (whether externally applied or internally created).
  • Figure 1 shows a schematic cross sectional of the setup used to form the metal matrix composite of Example 1;
  • Figure 2 is a photomicrograph at 400X magnification of the porous metal matrix composite body formed in Example 1.
  • the present invention relates to forming porous metal matrix composite bodies by spontaneously infiltrating a permeable mass of filler material or a preform with molten matrix metal.
  • an infiltration enhancer and/or an infiltration enhancer precursor and/or an infiltrating atmosphere are in communication with the filler material or preform, at least at some point during the process, which permits molten matrix metal to spontaneously infiltrate the filler material or preform.
  • the amount of matrix metal which infiltrates the filler material or preform is insufficient to embed substantially completely the filler material or preform.
  • a precursor to an infiltration enhancer may be supplied to at least one of a filler material or preform and/or a matrix metal and/or an infiltrating atmosphere.
  • the supplied infiltration enhancer precursor may thereafter react with at least one of the filler material or preform and/or the matrix metal and/or the 1 5 P infiltrating atmosphere to produce infiltration enhancer in at least a portion of, or on, the filler material or preform.
  • infiltration enhancer should be in contact with at least a portion of the filler material or preform.
  • an infiltration enhancer may be supplied directly to at least one of the preform and/or matrix metal and/or infiltrating atmosphere. Ultimately, at least during the spontaneous infiltration, the infiltration enhancer should be in contact with at least a portion of the filler material or preform.
  • a desired amount of molten matrix metal is contacted with the preform or filler material.
  • the preform or filler material may have admixed therewith, and/or at some point during the process, be exposed to, an infiltration enhancer precursor.
  • the molten matrix metal and/or preform or filler material communicate with an infiltrating atmosphere for at least a portion of the process.
  • the matrix metal and/or preform or filler material communicate with an infiltrating atmosphere for substantially all of the process.
  • the preform or filler material will be spontaneously infiltrated by molten matrix metal, and the extent or rate of spontaneous infiltration and formation of metal matrix composite will vary with a given set of processing conditions including, for example, the concentration of infiltration enhancer precursor provided to the system (e.g., in the molten matrix alloy and/or in the filler material or preform and/or in the infiltrating atmosphere), the size and/or composition of the filler material, the size and/or composition of particles in the preform, the available porosity for infiltration into the preform or filler material, the time permitted for infiltration to occur, and/or the temperature at which infiltration occurs.
  • concentration of infiltration enhancer precursor provided to the system (e.g., in the molten matrix alloy and/or in the filler material or preform and/or in the infiltrating atmosphere)
  • the size and/or composition of the filler material the size and/or composition of particles in the preform
  • the available porosity for infiltration into the preform or filler material the time
  • the physical and mechanical properties of the formed porous metal matrix composite bodies may be engineered to any particular application or need. For example, by providing a predetermined amount of filler material and by selecting the amount of matrix metal provided for infiltration, the amount of porosity within a formed metal matrix composite body can be controlled. Moreover, by varying the amount and/or composition of matrix metal provided to, e.g., one portion of a filler material or preform relative to another portion of the filler material or preform, the porosity in the metal matrix composite body may be tailored to suit a specific application.
  • the mechanical and/or physical properties may be further engineered to meet any particular application or need.
  • a post treatment process e.g., heat treatment, etc.
  • the processing conditions during the formation of a metal matrix composite the, e.g., nitrogen content, etc., of the formed metal matrix composite may be tailored to meet a wide range of industrial applications.
  • the composition and/or size (e.g., particle diameter) and/or geometry of the filler material or the material comprising the preform in combination with controlling the amount of matrix metal provided for infiltration, the physical and/or mechanical properties of the formed porous metal matrix composite can be controlled or engineered to meet any number of industrial needs.
  • a porous metal matrix composite body may be tailored depending on the loading of the filler material in the loose mass or in the preform and the amount of matrix metal provided for infiltration. Accordingly, a porous metal matrix composite body can be achieved by providing, for example, a loose mass or preform comprising a mixture of filler particles of varying sizes and/or shapes to achieve a relatively high loading, due to enhanced packing of the filler material, in combination with providing an amount of matrix metal which is insufficient to embed substantially completely the filler material or preform.
  • a loose mass or preform comprising a mixture of filler particles of varying sizes and/or shapes to achieve a relatively high loading, due to enhanced packing of the filler material, in combination with providing an amount of matrix metal which is insufficient to embed substantially completely the filler material or preform.
  • the density of a porous metal matrix composite body can be further reduced by providing a porous filler material or porous preform (e.g., a loosely packed filler material or preform and/or a hollow filler material) in combination with an amount of matrix metal which is sufficient only to coat the filler material.
  • a porous filler material or porous preform e.g., a loosely packed filler material or preform and/or a hollow filler material
  • the precise combination of filler material and amount of matrix metal provided depends upon the desired end use for the porous metal matrix composite body. Accordingly, by practicing any of the above teachings, alone or in combination, a porous metal matrix composite can be engineered to contain a desired combination of properties.
  • a metal matrix composite body may be formed by partially, or substantially completely, infiltrating a permeable mass of filler material or preform, and subsequently, leaching out at least a portion of the matrix metal from the composite body by, e.g., thermal etching, chemical etching, etc., to produce a porous metal matrix composite body.
  • Porous metal matrix composite bodies formed according to the method of the present invention may be tailored to suit a wide number of industrial applications.
  • porous metal matrix composite bodies may be tailored for use in such applications as thermal insulation materials, filters, strainers, etc.
  • a porous metal matrix composite body may be used as a preform for forming a metal matrix composite body by a spontaneous infiltration technique, or by an alternate metal matrix formation technique.
  • porous metal matrix composite bodies formed by the method of the present invention may be tailored to serve a wide variety of uses.
  • a simple lay-up 16 for forming a spontaneously infiltrated porous metal matrix composite in accordance with the present invention is illustrated.
  • a filler or preform 12 which may be of any suitable material, as discussed in detail below, is placed in a non-reactive vessel 10 for housing matrix metal and/or filler material.
  • a matrix metal 14 is placed on or adjacent to the filler or preform 12. The lay-up is thereafter placed in a furnace to initiate spontaneous infiltration.
  • the infiltration enhancer precursor when utilized in combination with, at least one of the matrix metal, and/or filler material or preform and/or infiltrating atmosphere, the infiltration enhancer precursor may react to form an infiltration enhancer which induces or assists molten matrix metal to spontaneously infiltrate a filler material or preform.
  • the precursor to the infiltration enhancer it appears as though it may be necessary for the precursor to the infiltration enhancer to be capable of being positioned, located or transportable to a location which permits the infiltration enhancer precursor to interact with at least one of the infiltrating atmosphere, and/or the preform or filler material, and/or molten matrix metal.
  • the infiltration enhancer precursor in some matrix metal/infiltration enhancer precursor/infiltrating atmosphere systems, it is desirable for the infiltration enhancer precursor to volatilize at, near, or in some cases, even somewhat above the temperature at which the matrix metal becomes molten.
  • volatilization may lead to: (1) a reaction of the infiltration enhancer precursor with the infiltrating atmosphere to form a gaseous species which enhances wetting of the filler material or preform by the matrix metal; and/or (2) a reaction of the infiltration enhancer precursor with the infiltrating atmosphere to form a solid, liquid or gaseous infiltration enhancer in at least a portion of the filler material or preform which enhances wetting; and/or (3) a reaction of the infiltration enhancer precursor within the filler material or preform which forms a solid, liquid or gaseous infiltration enhancer in at least a portion of the filler material or preform which enhances wetting.
  • an infiltration enhancer precursor was included or combined with, at least at some point during the process, molten matrix metal
  • the infiltration enhancer could volatilize from the molten matrix metal and react with at least one of the filler material or preform and/or the infiltrating atmosphere.
  • Such reaction could result in the formation of a solid species, if such solid species was stable at the infiltration temperature, said solid species being capable of being deposited on at least a portion of the filler material or preform as, for example, a coating.
  • solid species could be present as a discernable solid within at least a portion of the preform or filler material.
  • molten matrix metal may have a tendency to react (e.g., the molten matrix metal may reduce the formed solid species) such that infiltration enhancer precursor may become associated with (e.g., dissolved in or alloyed with) the molten matrix metal. Accordingly, additional infiltration enhancer precursor may then be available to volatilize and react with another species (e.g., the filler material or preform and/or infiltrating atmosphere) and again form a similar solid species.
  • infiltration enhancer precursor may then be available to volatilize and react with another species (e.g., the filler material or preform and/or infiltrating atmosphere) and again form a similar solid species.
  • an infiltration enhancer should be provided to the spontaneous system.
  • An infiltration enhancer could be formed from an infiltration enhancer precursor which could be provided (1) in the matrix metal; and/or (2) in the filler material or preform; and/or (3) from the infiltrating atmosphere; and/or (4) from an external source into the spontaneous system.
  • an infiltration enhancer may be supplied directly to at least one of the filler material or preform, and/or matrix metal, and/or infiltrating atmosphere.
  • the infiltration enhancer should be located in at least a portion of the filler material or preform.
  • the infiltration enhancer precursor can be at least partially reacted with the infiltrating atmosphere such that the infiltration enhancer can be formed in at least a portion of the filler material or preform prior to or substantially contiguous with contacting the filler material or preform with the matrix metal (e.g., if magnesium was the infiltration enhancer precursor and nitrogen was the infiltrating atmosphere, the infiltration enhancer could be magnesium nitride which would be located in at least a portion of the preform or filler material).
  • a matrix metal/infiltration enhancer precursor/infiltrating atmosphere system is the aluminum/magnesium/nitrogen system.
  • an aluminum matrix metal can be contained within a suitable refractory vessel which, under the process conditions, does not adversely react with the aluminum matrix metal and/or the filler material when the aluminum is made molten.
  • a filler material or preform can thereafter be contacted with molten aluminum matrix metal and spontaneously infiltrated.
  • an infiltration enhancer may be supplied directly to at least one of the preform or filler material, and/or matrix metal, and/or infiltrating atmosphere.
  • the infiltration enhancer should be located in at least a portion of the filler material or preform.
  • the preform or filler material should be sufficiently permeable to permit the nitrogen-containing gas to penetrate or permeate the filler material or preform at some point during the process and/or contact the molten matrix metal.
  • the permeable filler material or preform can accommodate infiltration of the molten matrix metal, thereby causing the nitrogen-permeated preform to be infiltrated spontaneously with molten matrix metal to form a metal matrix composite body and/or cause the nitrogen to react with an infiltration enhancer precursor to form infiltration enhancer in the filler material or preform and thereby result in spontaneous infiltration.
  • the extent of spontaneous infiltration and formation of the metal matrix composite will vary with a given set of process conditions, including magnesium content of the aluminum alloy, magnesium content of the preform or filler material, amount of magnesium nitride in the preform or filler material, the presence of additional alloying elements (e.g., silicon, iron, copper, manganese, chromium, zinc, and the like), average size of the filler material (e.g., particle diameter) comprising the preform or the filler material, surface condition and type of filler material or preform, nitrogen concentration of the infiltrating atmosphere, time permitted for infiltration and temperature at which infiltration occurs.
  • additional alloying elements e.g., silicon, iron, copper, manganese, chromium, zinc, and the like
  • average size of the filler material e.g., particle diameter
  • the aluminum can be alloyed with at least about 1 percent by weight, and preferably at least about 3 percent by weight, magnesium (which functions as the infiltration enhancer precursor), based on alloy weight.
  • magnesium which functions as the infiltration enhancer precursor
  • auxiliary alloying elements may also be included in the matrix metal to tailor specific properties thereof. Additionally, the auxiliary alloying elements may affect the minimum amount of magnesium required in the matrix aluminum metal to result in spontaneous infiltration of the filler material or preform. Loss of magnesium from the spontaneous system due to, for example, volatilization should not occur to such an extent that no magnesium was present to form infiltration enhancer.
  • the infiltrating atmosphere e.g., a nitrogen-containing gas
  • the infiltrating atmosphere can be supplied directly to the filler material or preform and/or matrix metal, or it may be produced or result from a decomposition of a material.
  • the minimum magnesium content required for the molten matrix metal to infiltrate a filler material or preform depends on one or more variables such as the processing temperature, time, the presence of auxiliary alloying elements such as silicon or zinc, the nature of the filler material, the location of the magnesium in one or more components of the spontaneous system, the nitrogen content of the atmosphere, and the rate at which the nitrogen atmosphere flows. Lower temperatures or shorter heating times can be used to obtain infiltration as the magnesium content of the alloy and/or preform is increased. Also, for a given magnesium content, the addition of certain auxiliary alloying elements such as zinc permits the use of lower temperatures.
  • a magnesium content of the matrix metal at the lower end of the operable range may be used in conjunction with at least one of the following: an above-minimum processing temperature, a high nitrogen concentration, or one or more auxiliary alloying elements.
  • an above-minimum processing temperature e.g., from about 1 to 3 weight percent
  • auxiliary alloying elements e.g., one or more auxiliary alloying elements.
  • alloys containing from about 3 to 5 weight percent magnesium are preferred on the basis of their general utility over a wide variety of process conditions, with at least about 5 percent being preferred when lower temperatures and shorter times are employed.
  • Magnesium contents in excess of about 10 percent by weight of the aluminum alloy may be employed to moderate the temperature conditions required for infiltration.
  • the magnesium content may be reduced when used in conjunction with an auxiliary alloying element, but these elements serve an auxiliary function only and are used together with at least the above-specified minimum amount of magnesium.
  • auxiliary alloying element for example, there was substantially no infiltration of nominally pure aluminum alloyed only with 10 percent silicon at 1000 ⁇ C into a bedding of 500 mesh, 39 Crystolon (99 percent pure silicon carbide from Norton Co.).
  • silicon has been found to promote the infiltration process.
  • the amount of magnesium varies if it is supplied exclusively to the preform or filler material. It has been discovered that spontaneous infiltration will occur with a lesser weight percent of magnesium supplied to the spontaneous system when at least some of the total amount of magnesium supplied is placed in the preform or filler material.
  • the preform may be desirable for a lesser amount of magnesium to be provided in order to prevent the formation of undesirable intermetallics in the metal matrix composite body.
  • a silicon carbide preform it has been discovered that when the preform is contacted with an aluminum matrix metal, the preform containing at least about 1% by weight magnesium and being in the presence of a substantially pure nitrogen atmosphere, the matrix metal spontaneously infiltrates the preform.
  • the amount of magnesium required to achieve acceptable spontaneous infiltration is slightly higher.
  • the magnesium in the aluminum/mangesium/nitrogen system, if the magnesium was applied to a surface of the matrix metal it may be preferred that the surface should be the surface which is closest to, or preferably in contact with, the permeable mass of filler material or vice versa; or such magnesium could be mixed into at least a portion of the preform or filler material. Still further, it is possible that some combination of surface application, alloying and placement of magnesium into at least a portion of the preform could be used. Such combination of applying infiltration enhancer(s) and/or infiltration enhancer precursor(s) could result in a decrease in the total weight percent of magnesium needed to promote infiltration of the matrix aluminum metal into the preform, as well as achieving lower temperatures at which infiltration can trcur. Moreover, the amount of undesirable intermetallics formed due to i, ⁇ e presence of magnesium could also be minimized.
  • auxiliary alloying elements and the concentration of nitrogen in the surrounding gas also affects the extent of nitriding of the matrix metal at a given temperature.
  • auxiliary alloying elements such as zinc or iron included in the alloy, or placed on a surface of the alloy, may be used to reduce the infiltration temperature and thereby decrease the amount of nitride formation, whereas increasing the concentration of nitrogen in the gas may be used to promote nitride formation.
  • the temperature required to effect the spontaneous infiltration process of this invention may be lower: (1) when the magnesium content of the alloy alone is increased, e.g., to at least about 5 weight percent; and/or (2) when alloying constituents are mixed with the permeable mass of filler material or preform; and/or (3) when another element such as zinc or iron is present in the aluminum alloy.
  • the temperature also may vary with different filler materials.
  • spontaneous and progressive infiltration will occur at a process temperature of at least about 675 ⁇ C, and preferably a process temperature of at least about 750 ⁇ C-800°C.
  • the spontaneous infiltration temperature is a temperature which is above the melting point of the matrix metal but below the volatilization temperature of the matrix metal. Moreover, the spontaneous infiltration temperature should be below the melting point of the filler material. Still further, as temperature is increased, the tendency to form a reaction product between the matrix metal and infiltrating atmosphere increases (e.g., in the case of aluminum matrix metal and a nitrogen infiltrating atmosphere, aluminum nitride may be formed). Such reaction product may be desirable or undesirable based upon the intended application of the metal matrix composite body. Additionally, electric resistance heating is typically used to achieve the infiltrating temperatures. However, any heating means which can cause the matrix metal to become molten and does not adversely affect spontaneous infiltration, is acceptable for use with the invention.
  • a permeable filler material or preform comes into contact with molten aluminum in the presence of, at least sometime during the process, a nitrogen-containing gas.
  • the nitrogen-containing gas may be supplied by maintaining a continuous flow of gas into contact with at least one of the filler material or preform and/or molten aluminum matrix metal.
  • the flow rate of the nitrogen-containing gas is not critical, it is preferred that the flow rate be sufficient to compensate for any nitrogen lost from the P T 0 atmosphere due to any nitride formation, and also to prevent or inhibit the incursion of air which can have an oxidizing effect on the molten metal .
  • suitable filler materials include (a) oxides, e.g. alumina, magnesia, zirconia; (b) carbides, e.g. silicon carbide; (c) borides, e.g. aluminum dodecaboride, titanium diboride, and (d) nitrides, e.g. aluminum nitride, and (e) mixtures thereof.
  • the filler material may comprise a substrate, such as carbon or other non-ceramic material, bearing - ceramic coating to protect the substrate from attack or degradation.
  • Suitable ceramic coatings include oxides, carbides, borides and nitrides. Ceramics which are preferred for use in the present method include alumina and silicon carbide in the form of particles, platelets, whiskers and fibers.
  • the fibers can be discontinuous (in chopped form) or in the form of continuous filament, such as multifilament tows.
  • the filler material or preform may be homogeneous or heterogeneous. It also has been discovered that certain filler materials exhibit enhanced infiltration relative to filler materials having a similar chemical composition. For example, crushed alumina bodies made by the method disclosed in U.S. Patent No. 4,713,360, entitled “Novel Ceramic Materials and Methods of Making Same", which issued on December 15, 1987, in the names of Marc S. Newkirk et al., exhibit desirable infiltration properties relative to commercially available alumina products. Moreover, crushed alumina bodies made by the method disclosed in Copending and Commonly Owned Application Serial No. 819,397, entitled “Composite Ceramic Articles and Methods of Making Same", in the names of Marc S. Newkirk et al .
  • the size, shape, chemistry and volume percent of the filler material can be any that may be required to achieve the properties desired in the composite.
  • the filler material may be in the form of particles, whiskers, platelets or fibers since infiltration is not restricted by the shape of the filler material. Other shapes such as spheres, tubules, pellets, refractory fiber cloth, and the like may be employed.
  • the size of the filler material does not limit infiltration, although a higher temperature or longer time period may be needed for infiltration of a mass of smaller particles than for larger particles or vice-versa depending on the particular reaction conditions.
  • Average particle diameters as small as a micron or less to about 1100 microns or more can be successfully utilized in the present invention, with a range of about 2 microns through about 1000 microns being preferred for a vast majority of commercial applications.
  • the mass of filler material (or preform) to be infiltrated should be permeable (i.e., contain at least some interconnected porosity to render it permeable to molten matrix metal and/or to the infiltrating atmosphere).
  • the size e.g., particle diameter
  • the physical and mechanical properties of the formed metal matrix composite can be controlled or engineered to meet any number of industrial needs.
  • wear resistance of the metal matrix composite can be increased by increasing the size of the filler material (e.g., increasing the average diameter of the filler material particles) given that the filler material has a higher wear resistance than the matrix metal.
  • strength and/or toughness may tend to increase with decreasing filler size.
  • the thermal expansion coefficient of the metal matrix composite may decrease with increasing filler loading, given that the coefficient of thermal expansion of the filler is lower than the coefficient of thermal expansion of the matrix metal.
  • the mechanical and/or physical properties (e.g., density, coefficient of thermal expansion, elastic and/or specific modulus, strength and/or specific strength, etc.) of a formed metal matrix composite body may be tailored depending on the loading of the filler material in the loose mass or in the preform.
  • a loose mass or 5 preform comprising a mixture of filler particles of varying sizes and/or shapes, wherein the density of the filler is greater than that of the matrix metal, a higher filler loading, due to enhanced packing of the filler materials, may be achieved, thereby resulting in a metal matrix composite body with an increased density.
  • the volume percent of filler material or preform which can be infiltrated can vary over a wide range.
  • the lower volume percent of filler that can be infiltrated is limited primarily by the ability to form a porous filler material or preform, (e.g., about 10 volume percent); whereas the higher volume percent of filler or preform that can be infiltrated is limited primarily by the ability to form a dense filler material or preform with at least some interconnected porosity (e.g., about 95 volume percent). Accordingly, by practicing any of the above teachings, alone or in combination, a metal matrix composite can be engineered to contain a desired combination of properties.
  • the method of forming metal matrix composites according to the present invention permits the production of substantially uniform metal matrix composites having a high volume fraction of filler material and tailorable porosity.
  • Higher volume fractions of filler material may be achieved by using a lower porosity initial mass of filler material.
  • Higher volume fractions also may be achieved if the mass of filler is compacted or otherwise densified provided that the mass is not converted into either a compact with closed cell porosity or into a fully dense structure that would prevent infiltration by the molten alloy.
  • volume fractions on the order of about 60 to 80 volume percent can be achieved by methods such as vibrational packing, controlling particle size distribution, etc.
  • alternative techniques can be utilized to achieve even higher volume fractions of filler.
  • Volume fractions of filler on the order of 40 to 50 percent are preferred for thermo-forming in accordance with the present invention. At such volume fractions, the infiltrated composite maintains or substantially maintains its shape, thereby facilitating secondary processing.
  • Higher or lower particle loadings or volume fractions could be used, however, depending on the desired final composite loading after thermo-forming.
  • methods for reducing particle loadings can be employed in connection with the thermo-forming processes of the present invention to achieve lower particle loadings.
  • wetting of the ceramic filler by the aluminum matrix metal may be an important part of the infiltration mechanism. Further, the wetting of the filler by molten matrix metal may permit a uniform dispersion of the filler throughout the formed metal matrix composite and improve the bonding of the filler to the matrix metal. Moreover, at low processing temperatures, a negligible or minimal amount of metal nitriding occurs resulting in a minimal discontinuous phase of aluminum nitride dispersed in the metal matrix. However, as the upper end of the temperature range is approached, nitridation of the metal is more likely to occur.
  • the amount of the nitride phase in the metal matrix can be controlled by varying the processing temperature at which infiltration occurs.
  • the specific process temperature at which nitride formation becomes more pronounced also varies with such factors as the matrix aluminum alloy used and its quantity relative to the volume of filler or preform, the filler material to be infiltrated, and the nitrogen concentration of the infiltrating atmosphere.
  • the extent of aluminum nitride formation at a given process temperature is believed to increase as the ability of the alloy to wet the filler decreases and as the nitrogen concentration of the atmosphere increases.
  • the process conditions can be selected to control the nitride formation.
  • a composite product containing an aluminum nitride phase will exhibit certain properties which can be favorable to, or improve the performance of, the product.
  • the temperature range for spontaneous infiltration with an aluminum alloy may vary with the ceramic material used. In the case of alumina as the filler material, the temperature for infiltration should preferably not exceed about 1000 ⁇ C if it is desired that the ductility of the matrix not be reduced by the significant formation of nitride. However, temperatures exceeding
  • 1000 ⁇ C may be employed if it is desired to produce a composite with a less ductile and stiffer matrix.
  • higher temperatures of about 1200°C may be employed since the aluminum alloy nitrides to a lesser extent, relative to the use of alumina as filler, when silicon carbide is employed as a filler material.
  • the constituency of the metal matrix may be modified after formation of the metal matrix composite.
  • exposure of the formed metal matrix composite to a heat treatment may improve the tensile strength of the metal matrix composite.
  • a desirable heat treatment for a metal matrix composite containing a 520.0 aluminum alloy as the matrix metal may comprise heating the metal matrix composite to an elevated temperature, for example, to about 430 ⁇ C, which is maintained for an extended period (e.g., 18-20 hours).
  • the metal matrix may then be quenched in boiling water at about 100'C for about 20 seconds (i.e., a T-4 heat treatment) which can temper or improve the ability of the composite to withstand tensile stresses, Moreover, it may be desirable to subject a formed metal matrix composite body to, e.g., a carburizing or boronizing environment to improve, for example, the corrosion resistance, etc., of the metal matrix composite body.
  • a formed metal matrix composite body e.g., a carburizing or boronizing environment to improve, for example, the corrosion resistance, etc., of the metal matrix composite body.
  • a matrix metal in the reservoir which differs in composition from the first source of matrix metal.
  • a matrix metal in the reservoir which differs in composition from the first source of matrix metal.
  • an aluminum alloy is used as the first source of matrix metal
  • virtually any other metal or metal alloy which was molten at the processing temperature could be used as the reservoir metal. Molten metals frequently are very miscible with each other which would result in the reservoir metal mixing with the first source of matrix metal so long as an adequate amount of time is given for the mixing to occur.
  • a reservoir metal which is different in composition from the first source of matrix metal it is possible to tailor the properties of the metal matrix to meet various operating requirements and thus tailor the properties of the metal matrix composite.
  • barrier means may also be utilized in combination with the present invention.
  • the barrier means for use with this invention may be any suitable means which interferes, inhibits, prevents or terminates the migration, movement, or the like, of molten matrix alloy (e.g., an aluminum alloy) beyond the defined surface boundary of the filler material.
  • Suitable barrier means may be any material, compound, element, composition, or the like, which, under the process conditions of this invention, maintains some integrity, is not volatile and preferably is permeable to the gas used with the process, as well as being capable of locally inhibiting, stopping, interfering with, preventing, or the like, continued infiltration or any other kind of movement beyond the defined surface boundary of the ceramic filler.
  • Barrier means may be used during spontaneous infiltration or in any molds or other fixtures utilized in connection with thermo-forming of the spontaneously infiltrated metal matrix composite, as discussed in greater detail below.
  • Suitable barrier means includes materials which are substantially non-wettable by the migrating molten matrix alloy under the process conditions employed.
  • a barrier of this type appears to exhibit little or no affinity for the molten matrix alloy, and movement beyond the defined surface boundary of the filler material or preform is prevented or inhibited by the barrier means.
  • the barrier reduces any final machining or grinding that may be required of the metal matrix composite product.
  • the barrier preferably should be permeable or porous, or rendered permeable by puncturing, to permit the gas to contact the molten matrix alloy.
  • Suitable barriers particularly useful for aluminum matrix alloys are those containing carbon, especially the crystalline allotropic form of carbon known as graphite.
  • Graphite is essentially non-wettable by the molten aluminum alloy under the described process conditions.
  • a particular preferred graphite is a graphite foil product that is sold under the trademark Grafoil ® , registered to Union Carbide. This graphite foil exhibits sealing characteristics that prevent the migration of molten aluminum alloy beyond the defined surface boundary of the filler material. This graphite foil is also resistant to heat and is chemically inert.
  • Grafoil® graphite foil is flexible, compatible, conformable and resilient. It can be made into a variety of shapes to fit any barrier application.
  • graphite barrier means may be employed as a slurry or paste or even as a paint film around and on the boundary of the filler material or preform.
  • Grafoil ® is particularly preferred because it is in the form of a flexible graphite sheet. In use, this paper-like graphite is simply formed around the filler material or preform.
  • transition metal borides e.g., titanium diboride (TiB )
  • TiB titanium diboride
  • the process temperature should not exceed about 875 * C, for otherwise the barrier material becomes less efficacious and, in fact, with increased temperature infiltration into the barrier will occur.
  • the particle size of the barrier material may affect the ability of the material to inhibit spontaneous infiltration.
  • the transition metal borides are typically in a particulate form (1-30 microns).
  • the barrier materials may be applied as a slurry or paste to the boundaries of the permeable mass of ceramic filler material which preferably is preshaped as a preform.
  • barrier barriers for aluminum metal matrix alloys in nitrogen include low-volatile organic compounds applied as a film or layer onto the external surface of the filler material or preform. Upon firing in nitrogen, especially at the process conditions of this invention, the organic compound decomposes leaving a carbon soot film.
  • the organic compound may be applied by conventional means such as painting, spraying, dipping, etc.
  • finely ground particulate materials can function as a barrier so long as infiltration of the particulate material would occur at a rate which is slower than the rate of infiltration of the filler material .
  • the barrier means may be applied by any suitable means, such as by covering the defined surface boundary with a layer of the barrier means.
  • a layer of barrier means may be applied by painting, dipping, silk screening, evaporating, or otherwise applying the barrier means in liquid, slurry, or paste form, or by sputtering a vaporizable barrier means, or by simply depositing a layer of a solid particulate barrier means, or by applying a solid thin sheet or film of barrier means onto the defined surface boundary.
  • Figure 1 is a cross-sectional schematic of the setup 16 used to form a porous metal matrix composite body. Specifically, a Grade ATJ graphite boat (Union Carbide Corporation, Carbon Product Division, Cleveland, OH) measuring about 3 inches (76 mm) long by about 3 inches (76 mm) wide by about 2.5 inches (64 mm) high, and having a wall thickness of about 0.5 inch (13 mm), was lined with a graphite foil box 11.
  • a Grade ATJ graphite boat Union Carbide Corporation, Carbon Product Division, Cleveland, OH
  • the graphite foil box 11 had been formed from a piece of PERMAFOIL ® graphite foil (TT America, Portland, OR) measuring about 6 inches (152 mm) long by about 6 inches (152 mm) wide by about 0.010 inch (0.25 mm) thick, which was cut and folded to fit within the inner dimensions of the graphite boat,
  • a filler material mixture 12 was prepared by ball milling a mixture comprising, by weight, about 95% 38 ALUNDUM® 500 grit alumina (Norton Co., Worcester, MA) and about 5% -325 mesh magnesium powder. Specifically, the filler material mixture was placed into a plastic jar and ball milled for about an hour, then the filler material mixture was dried at a temperature of about 150 ⁇ C for about 1 hour.
  • the retort was evacuated to a vacuum of about 30 inches (762 mm) of mercury, then the vacuum pump was shut off and a nitrogen atmosphere flowing at about 15 liters per minute was introduced into the retort chamber.
  • the furnace and its contents were then heated to a temperature of about 500 ⁇ C at a rate of about 400 ⁇ C, held at about 500 ⁇ C for about an hour, then heated to about 750°C at a rate of about 400 ⁇ C per hour. After about 3 hours at about 750°C, the flowing nitrogen atmosphere and the power to the furnace were shut off, and the setup was cooled to room temperature.
  • FIG. 1 is a photomicrograph of the sample, taken at about 400X magnification, showing the interconnected nature of the filler material particles, as well as the porosity between the alumina filler material.

Abstract

Cette invention concerne un nouveau procédé pour former des corps composites à matrice métallique poreuse. Une particularité de ce procédé réside dans le fait qu'un stimulateur d'infiltration et/ou un précurseur de stimulateur d'infiltration et/ou une atmosphère infiltrante sont en communication avec un matériau de remplissage ou une préforme, au moins à un moment pendant la fabrication, ce qui permet au métal matriciel fondu de s'infiltrer spontanément dans le matériau de remplissage ou dans la préforme. Cette infiltration spontanée s'effectue sans qu'il soit nécessaire d'appliquer une pression ou de créer un vide. Toutefois, la quantité de métal matriciel prévue est insuffisante pour noyer complètement le matériau de remplissage ou la préforme.
PCT/US1991/003160 1990-05-09 1991-05-07 Composites a matrice metallique poreuse et procedes de fabrication WO1991017275A1 (fr)

Priority Applications (1)

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JP91510410A JPH05507122A (ja) 1990-05-09 1991-05-07 多孔性金属母材複合材料と製造方法

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999032678A2 (fr) * 1997-12-19 1999-07-01 Advanced Materials Lanxide, Llc Corps composite de matrice metallique dote d'une surface a usinabilite accrue et a pouvoir abrasif reduit
US6635357B2 (en) 2002-02-28 2003-10-21 Vladimir S. Moxson Bulletproof lightweight metal matrix macrocomposites with controlled structure and manufacture the same

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3384464A (en) * 1966-02-16 1968-05-21 Mallory & Co Inc P R Tungsten structures
EP0291441A1 (fr) * 1987-05-13 1988-11-17 Lanxide Technology Company, Lp. Matériaux composites à matrice métallique

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3384464A (en) * 1966-02-16 1968-05-21 Mallory & Co Inc P R Tungsten structures
EP0291441A1 (fr) * 1987-05-13 1988-11-17 Lanxide Technology Company, Lp. Matériaux composites à matrice métallique

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999032678A2 (fr) * 1997-12-19 1999-07-01 Advanced Materials Lanxide, Llc Corps composite de matrice metallique dote d'une surface a usinabilite accrue et a pouvoir abrasif reduit
WO1999032678A3 (fr) * 1997-12-19 1999-08-26 Lanxide Technology Co Ltd Corps composite de matrice metallique dote d'une surface a usinabilite accrue et a pouvoir abrasif reduit
US6517953B1 (en) * 1997-12-19 2003-02-11 Lanxide Technology Company, Lp Metal matrix composite body having a surface of increased machinability and decreased abrasiveness
US6635357B2 (en) 2002-02-28 2003-10-21 Vladimir S. Moxson Bulletproof lightweight metal matrix macrocomposites with controlled structure and manufacture the same

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