WO1999032418A2

WO1999032418A2 - Improved method for making a metal matrix composite body by an infiltration process

Info

Publication number: WO1999032418A2
Application number: PCT/US1998/026948
Authority: WO
Inventors: Gerhard Hans Schiroky; William Fischer; Michael K. Aghajanian; Robert Wiener
Original assignee: Lanxide Technology Company, Lp
Priority date: 1997-12-19
Filing date: 1998-12-18
Publication date: 1999-07-01
Also published as: WO1999032418A8; AU2087999A; WO1999032418A3

Abstract

Improvements in processing metal matrix composite materials by infiltration are disclosed. Specifically, a permeable mass comprising a preform or bedding material is provided to an infiltration setup in addition to that being the objective of the infiltration. The additional preform or bed is itself infiltrated at least at some point during processing to produce an additional, e.g., 'sacrificial' MMC body. This sacrificial MMC reduces the amount that the carcass of matrix metal may shrink during cooling which in turn reduces the stress on and warping induced in the objective preform. The second or additional bed or preform is termed a 'sacrificial' bed or sacrificial preform. The sacrificial bed or preform may be disposed between the object preform and the body of matrix metal, or opposite the body of matrix metal from the object preform, or both. The sacrificial MMC may be reused in subsequent infiltration setups to produce additional infiltrations of objective preforms. Further, a separation facilitator may be disposed between the objective preform and the sacrificial bedding/preform/MMC to assist in the recovery of the desired MMC body following infiltration and solidification of matrix metal.

Description

IMPROVED METHOD FOR MAKING A METAL MATRIX COMPOSITE BODY BY AN INFILTRATION PROCESS

TECHNICAL FIELD

The present invention relates to techniques for producing metal matrix composite bodies. In particular, the present invention relates to a technique for ameliorating thermal expansion related stress developed during infiltration.

BACKGROUND ART

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. Generally, a metal matrix composite ("MMC") will show an improvement in such properties as strength, stiffness, contact wear resistance, 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 stiffness, wear resistance and high temperature strength relative to aluminum.

Although various powder metallurgical techniques have been developed over the years to produce MMC bodies, the infiltration or casting approaches seem to be preferred by present manufacturers. Particularly preferred is infiltration of a mass of ceramic material by a molten matrix metal which does not require an assist by pressure or vacuum (whether externally applied or internally created). Such infiltration has been termed "spontaneous infiltration."

Typically, it is desirable to supply a quantity of matrix metal which is greater than that needed to fill the interstices between the filler material to produce the MMC body. Due to the nature of the infiltration process, upon completion of infiltration there remains a continuous pathway of matrix metal extending from the carcass of matrix metal into the MMC body. Further, the coefficient of thermal expansion (CTE) of the body of matrix metal typically is very different from that of the MMC body. Thus, upon completion of infiltration, e.g., during cooling, the carcass shrinks at a greater rate than does the MMC body. Upon solidification of the matrix metal, the differential shrinkage rates generate stress. Particularly where thin MMC bodies are concerned, the stresses generated can be large enough to crack or at least warp the body. Even if a warped MMC body is salvageable, the body will require additional processing, e.g., machining to return it to the required shape.

Commonly Owned U.S. Patent No. 5,172,747 to Aghajanian et al. teaches a number of techniques to ameliorate this stress-induced cracking and warping. Specifically, a gating means is disposed between the body of matrix metal and the preform or permeable mass of filler material to be infiltrated. The gating means reduces the stress intensity by reducing the area of contact between the carcass of matrix metal and the formed MMC body. In one embodiment, the gating means takes the form of a riser or spacer to physically separate the MMC body from direct contact with the body of matrix metal. In a preferred embodiment, such a "riser ring" is filled with ceramic filler material in an effort to move the CTE mismatch region away from the MMC body. This commonly-owned U.S. Patent also teaches the concept of "separation facilitators", materials which are placed between the body of matrix metal and the preform or permeable mass of filler material to be infiltrated. The purpose of the separation facilitator is to cause the carcass to physically separate from the formed MMC body upon cooling and before the developing thermally-induced stresses become excessive.

DESCRIPTION OF COMMONLY OWNED U.S. PATENTS

Commonly owned U.S. Patent No. 4,828,08 to White et al. teaches a technique for producing a MMC body by a spontaneous infiltration process. According to the White et al invention, a permeable mass of ceramic filler material may be infiltrated by a molten aluminum alloy containing at least 1 weight % magnesium in the presence of a gas comprising from about 10 to 100 volume % nitrogen without the requirement for pressure or vacuum (whether externally applied or internally created). In one embodiment of the White et al. invention, the formed MMC body is provided with an aluminum nitride skin or surface. Specifically, if the supply of molten aluminum alloy matrix metal becomes exhausted before complete infiltration of the permeable ceramic filler material, an aluminum nitride layer or zone may form on or along the outer surface of the MMC. Also, an aluminum nitride skin can be formed at the exterior surface of the permeable mass of ceramic filler material by prolonging the process conditions. In particular, once infiltration of the permeable ceramic material is substantially complete if the infiltrated ceramic material is further exposed to the nitrogenous atmosphere at substantially the same temperature at which infiltration occurred, the molten aluminum at the exposed surface will nitride. The degree of nitridation can be controlled and may be formed as either a continuous phase or discontinuous phase in the skin layer.

Commonly owned U.S. Patent No. 5,298,339, teaches the production of metal matrix composite bodies using a reservoir feed method. Particularly, the metal is initially present as a first source and as a reservoir. The first source and reservoir communicating with each other such that a sufficient amount of metal is present to permeate completely the permeable mass of filler material. Still further, if desirable, the reservoir can contain and excess amount of metal (i.e., more metal can be present than that amount which is needed for complete infiltration) and such excess metal can be bonded directly to the ceramic-filled metal matrix composite, thus forming a novel complex composite body comprising a metal bonded to a metal matrix composite body.

Commonly owned U.S. Patent No. 5,172,747 to Aghajanian et al. teaches a method for producing MMC bodies by an infiltration process whereby an interface between matrix metal and the permeable mass of filler material or preform to be infiltrated has included in at least a portion thereof an infiltration enhancer and/or an infiltration enhancer precursor. According to Aghajanian et al. the presence of magnesium on a surface of both the filler material or preform and/or on a surface of the matrix metal may result in a reduction in the required amount of magnesium to achieve spontaneous infiltration.

As discussed above, commonly owned U.S. Patent No. 5,553,657 to Aghajanian et al. teaches the use of a gating means in combination with various metal infiltration processes which may be utilized to produce a MMC body. Particularly, a permeable mass of filler material or a preform is infiltrated by molten matrix metal (e.g., spontaneously, by pressure infiltration, by vacuum infiltration, etc.) to form a MMC body. A gating means is provided which controls or limits the area of contact between molten matrix metal and the filler material or preform. Such limited or controlled area contact may result in less required machining of a formed MMC body to achieve a net or near-net shape body as compared to a similar MMC body made without a gating means. Moreover, the use of a gating means ameliorates the tendency of a formed MMC body to warp due to the contact and bonding between the formed composite body and matrix metal carcass. The gating means may comprise a substantially impermeable material (under the process conditions) such as a graphite foil sheet through which one or more holes have been cut to permit passage of molten matrix metal therethrough.

The gating means may also comprise a ring or tube placed between the source of matrix metal and the permeable mass or preform to be infiltrated. Such a "riser ring" confines the molten metal to the tube or ring interior on its way from the matrix metal source to the permeable mass or preform to be infiltrated. Optionally, the riser ring or tube may contain one or more substantially inert filler materials, such as ceramic particulate. The gating means still further may comprise a material permeable to the molten matrix metal under the process conditions, or a material containing channels through which the molten metal may pass. Also defined as gating means are materials which assist in the separation of the formed MMC article from the carcass of matrix metal upon conclusion of the infiltration process. Such materials are sometimes specifically referred to as "separation means" or "separation facilitators." Metal foils, and reducible oxides and nitrides are examples of separation facilitator materials. DISCLOSURE OF THE INVENTION

The present invention amplifies on the teachings of the above-identified Aghajanian '657 patent. Specifically, the present invention recognizes and appreciates that supplying the matrix metal not from a body of molten metal in direct contact with the permeable mass or preform to be infiltrated, but instead supplying this metal from an interposed MMC body, contributes to reduction in potential warpage due to thermal expansion coefficient mismatches, as well as contributes to facilitated separation and recovery of the object MMC body. The MMC interposed between the body of molten matrix metal and the permeable mass or preform to be infiltrated may be any whose matrix metal is reasonably similar in composition to the desired matrix metal phase of the object MMC to be formed. This interposed MMC termed the

"sacrificial MMC", may be formed in situ during formation of the object MMC body or it may be provided as a pre-existing MMC body made by any process for producing MMC bodies.

A sacrificial MMC body which is formed in situ may be provided in the form of a self- supporting preform to be infiltrated or as non-self-supporting bedding or permeable mass of filler material to be infiltrated.

The sacrificial MMC may contact a portion of a surface of the object preform to be infiltrated, may be substantially co-extensive with a surface of the object preform or may be in proximate contact with more than one surface of the preform to be infiltrated. To further facilitate separation and recovery of the object MMC body, the sacrificial MMC may feature a release coating or separation facilitator layer disposed on the surface contacting the object preform.

The sacrificial MMC body need not be discarded following the formation of the object MMC by infiltration. Instead, all that may be necessary may be to resupply sufficient matrix metal, with any necessary alloying elements, in contact with one face or surface of the sacrificial MMC body to be able to supply sufficient matrix metal for infiltrating the next object preform. In this way, substantial resources are conserved by not having to provide a new sacrificial MMC body (or to make a new sacrificial MMC body in situ) every time a new object MMC is to be produced.

Additionally it has been discovered that the sacrificial MMC need not be disposed between the body of molten matrix metal and the object preform to achieve warpage reductions due to management of the CTE mismatches. In particular, it has been observed that merely placing the sacrificial MMC in contact with the body of matrix metal opposite that of the object preform is effective in reducing CTE mismatch induced stresses. A sacrificial MMC (or its precursor, preform or bedding materials) arranged in this way is sometimes referred to as "a stress control layer". BRIEF DESCRIPTION OF THE FIGURES

Figures 1 and 2 are cross-sectional schematic views of setups which represent various embodiments of managing the thermal expansion mismatch between an objective mass or preform and a body of matrix metal through the use of a sacrificial bed or preform; Figure 3 is a cross-sectional schematic view of a setup used in accordance with

Example 1 ;

Figure 4 is a cross-sectional schematic view of a setup used to produce the metal matrix composite body of Example 2;

Figure 5 is a cross-sectional schematic view of a setup used to produce the metal matrix composite body of Example 3 ;

Figure 6 is a cross-sectional schematic view of a setup used to produce the metal matrix composite body of Example 4;

Figure 7 is a cross-sectional view of the various materials employed in creating the setup of Example 6; and Figure 8 is a cross-sectional schematic view of a setup used to produce the metal matrix composite brake caliper piston of Example 8.

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", as used herein, 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). Further, 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. "Carcass" or "Carcass of Matrix Metal", as used herein, refers to any of the original body of matrix metal remaining which has not been 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. "Filler", as used herein, 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, 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.

"Infiltrating Atmosphere", as used herein, 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", as used herein, 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. Moreover, 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. Ultimately, at least during the spontaneous infiltration, 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. Without wishing to be bound by any particular theory or explanation, 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 metal. For example, 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. Such 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.

"Matrix 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). When 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 is the major or predominant constituent.

"Matrix 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-dimensionally 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).

"Object or Objective Preform", as used herein, refers to the preform the infiltration of which by matrix metal yields a metal matrix composite body which has utility other than utility for assisting in the infiltration of additional object preforms. "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", as used herein, 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.

"Sacrificial Bed" or "Sacrificial Preform", as used herein, means a permeable mass of filler material which is to be infiltrated by molten matrix metal to form a metal matrix composite body whose role is to assist in the formation of a different metal matrix composite body.

"Sacrificial MMC". as used herein, means a metal matrix composite body whose role is to assist in the production of a different metal matrix composite body. A sacrificial MMC" may be a metal matrix composite body produced as a result of the infiltration of a sacrificial bed or preform by a molten matrix metal, or it may be a pre-existing metal matrix composite body. "Spontaneous Infiltration", as used herein, means the infiltration of matrix metal into the permeable mass of filler or preform occurs without the requirement for the application of pressure or vacuum (whether externally applied or internally created).

"Stress Control Layer" or "Stress Balancer", as used herein, means a sacrificial bed or preform whose function includes reducing the extent of thermal expansion coefficient mismatch between the body of matrix metal and the object preform. MODES FOR CARRYING OUT THE INVENTION

When a metal matrix composite body is produced by infiltrating a body of molten matrix metal into an adjoining permeable mass of filler material, typically a leftover portion or "carcass" of matrix metal remains behind and remains attached to the composite body. One problem presented by an infiltrated preform, e.g., metal matrix composite body, remaining attached to the carcass of matrix metal arises from the difference in thermal expansion coefficients associated therewith. In particular, on cooling, the carcass of matrix metal shrinks faster than does the MMC. If the two pieces remain bonded after solidification of the matrix metal, the difference in shrinkage rates results in the development of stresses: on average, an overall compressive stress is placed on the MMC and a tensile stress on the carcass.

The stresses can be sufficiently large to cause cracking of the MMC. The problem is particularly likely to occur in thin MMC bodies. Even if cracking does not occur, the stresses can cause warping of the MMC body, especially for MMC bodies of low cross-sectional area, e.g., thin bodies. It has been discovered that interposing an additional MMC body, e.g., a sacrificial

MMC body, or an additional permeable mass or preform to be infiltrated, e.g., sacrificial bed or preform, between the object mass or preform and the body of matrix metal, permits the interposed body to be the repository for the cracking or stress-induced warping instead of the desired MMC. Once this sacrificial body has been separated from the desired MMC and the carcass of matrix metal, it may be reused, discarded or recycled. Specifically, and with reference to Figure 1, a body of matrix metal 11 is supported by a non-infiltratable bedding material 13 housed in refractory boat 15. Sacrificial preform 17 is disposed between object preform 19 and body of matrix metal 11 and contacts each. Under spontaneous infiltration conditions molten matrix metal 11 spontaneously infiltrates sacrificial preform 17 to form a sacrificial metal matrix composite body. The molten matrix metal within sacrificial MMC continues to spontaneously infiltrate upwards into object preform 19 to form the desired or objective MMC body.

Moreover, it has been somewhat surprisingly discovered that the stress reducing properties of the sacrificial MMC body work even when the sacrificial body is placed on the side of the body of matrix metal opposite the object preform. Without wishing to be bound by any one particular theory or explanation, it appears that the constraining of the body of matrix metal by the sacrificial MMC extends through the thickness of the body of matrix metal. Thus, the regions or zones of matrix metal near the object preform are also constrained by the sacrificial MMC. Specifically, and with reference to Figure 2, body of matrix metal 11 , sacrificial preform 17 and object preform 19 are supported by a non-infiltratable bedding material 13 housed in refractory boat 15. In particular, body of matrix metal 11 is disposed between object preform 19 and sacrificial preform 17 and contacting each. During spontaneous infiltration, molten matrix metal from body of matrix metal 1 1 spontaneously infiltrates object preform 19 to form the objective MMC. Furthermore, matrix metal also spontaneously infiltrates sacrificial preform 17 to form a sacrificial MMC body although not necessarily simultaneously with the spontaneous infiltration of object preform 19. During solidification of the matrix metal, the sacrificial MMC constrains the shrinkage of the carcass or body of uninfiltrated matrix metal, thereby reducing the amount of stress generated at interface 21 due to the different thermal expansion coefficients of the carcass and the formed MMC body.

In carrying out the method of the present invention, it is not necessary that a preform or permeable bedding be used as the material to be infiltrated to form the sacrificial MMC body. Instead, a pre-existing MMC body may be designated the sacrificial MMC. Such a sacrificial

MMC could be contacted to the body of matrix metal in exactly the same way as a sacrificial bedding or preform. In the embodiment in which such a sacrificial MMC is disposed between the object preform and the body of matrix metal, the matrix metal in the objective MMC may derive, at least in part, from the matrix metal making up the sacrificial MMC. In the embodiment in which a sacrificial preform or sacrificial MMC is disposed between the body or reservoir of matrix metal and the object preform, the sacrificial preform or sacrificial MMC may contact only a portion of one surface of the object preform, may be substantially coextensive with a surface or may be in contact with more than a single surface of the object preform. The sacrificial MMC exhibits a number of useful characteristics of a gating means (as taught in U.S. Patent No. 5,553,657 to Aghajanian et al., discussed above). In particular, the sacrificial MMC often serves to reduce or eliminate the warping and potential cracking of the object MMC due to the thermal expansion mismatch between the body of matrix metal and the object MMC. The inherent gating properties of the sacrificial MMC, however, can be enhanced through the use of other gating means and/or separation facilitators. The gating means and/or separation facilitator may be disposed in any zone between the object MMC and the sacrificial MMC. Separation facilitators, such as metal foils and gating means such as graphite foil sheets which have been rendered permeable to molten matrix metal (as for example by puncturing), are not normally associated with either the sacrificial MMC or the object preform. Other types of separation facilitators and gating means, however, such as reducible oxides or nitrides or permeable materials such as relatively thin layers of colloidal graphite, are normally associated with one or both of the sacrificial MMC and the object preform. For example, a sacrificial MMC or sacrificial preform may feature a coating of thinly applied colloidal graphite to further reduce the areal contact between molten matrix metal and the object MMC body, thereby assisting in the separation of the object MMC body from the remainder of the setup following infiltration and solidification. The ability to coat gating means or separation facilitators onto the sacrificial preform or sacrificial MMC is significant because certain object preforms cannot be so coated, or can be coated only with great difficulty and with less than optimum results (e.g., when the object preform is highly porous).

The sacrificial MMC body need not be discarded following the formation of the object MMC by infiltration. Instead, all that may be necessary may be to resupply sufficient matrix metal, with any necessary alloying elements, in contact with one face or surface of the sacrificial MMC body to be able to supply sufficient matrix metal for infiltrating the next object preform. In this way, substantial resources are conserved by not having to provide a new sacrificial MMC body (or to make a new sacrificial MMC body in situ) every time a new object MMC is to be produced. If the sacrificial MMC body is to be reused, it may be desirable to dispose a gating means or separation facilitator between the sacrificial MMC and the body of matrix metal.

Further, the present invention is illustrated largely in the context of spontaneous infiltration, whereby a molten matrix metal is caused to infiltrate a permeable mass or preform of filler material without the requirement for an assist from pressure or vacuum, whether externally applied or internally generated. It should be understood, however, that the inventors do not believe that the present invention is limited to spontaneous infiltration systems. Instead, the present invention should be operative in infiltration systems which utilize pressure or vacuum assists, as well as in pressureless infiltration systems.

At this point, however, a more detailed discussion of the phenomenon of spontaneous infiltration is in order.

In order to effect spontaneous infiltration of the matrix metal into the filler material or preform, 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. Moreover, rather than supplying an infiltration enhancer precursor, 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. Ultimately, at least during the spontaneous infiltration, the infiltration enhancer should be located in at least a portion of the filler material or preform. Without wishing to be bound by any particular theory or explanation, when an infiltration enhancer precursor is 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. Moreover, 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. For example, 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. Such volatilization may lead to: (1) a reaction of the infiltration enhancer precursor with the infiltrating atmosphere to form a solid liquid or gaseous infiltration enhancer which enhances wetting of the filler material or preform by the matrix metal; or (2) 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. Thus, for example, if an infiltration enhancer precursor were included or combined with molten matrix metal at least at some point during the process, it is possible that the infiltration enhancer precursor 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 is 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. Moreover, it is conceivable that such solid species could be present as a discernible solid within at least a portion of the preform or filler material. If such a solid species were formed, 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. It is conceivable that a continuous process of conversion of infiltration enhancer precursor to infiltration enhancer followed by a reduction reaction of the infiltration enhancer with molten matrix metal to again form additional infiltration enhancer precursor, and so on, could occur, until the result achieved is a spontaneously infiltrated metal matrix composite.

In a preferred embodiment of the invention, it is possible that 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 were the infiltration enhancer precursor and nitrogen were 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). Under the conditions employed in the method of the present invention, in the case of an aluminum/magnesium/nitrogen spontaneous infiltration system, 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. Moreover, 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. For example, for infiltration of the molten aluminum matrix metal to occur spontaneously, 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. Auxiliary alloying elements, as discussed above, 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 aluminum matrix 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. Still further, the presence of magnesium in both of the preform (or filler material) and matrix metal may result in a reduction in the total required amount of magnesium to achieve spontaneous infiltration. Additionally, such placement of the magnesium may permit lowering of the temperature at which infiltration occurs, and/or may reduce the amount of undesirable magnesium-containing intermetallics .

It has been noted that it is possible to supply to the spontaneous system infiltration enhancer precursor and/or infiltration enhancer on a surface of the alloy and/or on a surface of the preform or filler material and/or within the preform or filler material and/or from an external source prior to infiltrating the matrix metal into the filler material prior to infiltrating the matrix metal into the filler material or preform. For example, in the aluminum/magnesium/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.

The concentration of magnesium in the alloy, and/or placed onto a surface of the alloy, and/or combined in the filler or preform material, also tends to affect the extent of infiltration at a given temperature. 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; 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. In general, in the aluminum/magnesium/nitrogen system 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.

In the embodiment in which an infiltration enhancer such as magnesium nitride is produced in situ by chemically reacting a magnesium containing infiltration enhancer precursor with a nitrogen containing infiltrating atmosphere, it is not necessary to maintain the presence of the nitrogen containing atmosphere throughout the entire infiltration process. Specifically, once sufficient infiltration enhancer has been produced, the infiltration of the molten matrix metal into the permeable mass or preform may be conducted under vacuum or under a different infiltrating atmosphere such as an atmosphere which is chemically inert with respect to at least the infiltration enhancer precursor, for example, argon.

The method of forming a metal matrix composite is applicable to a wide variety of filler materials, and the choice of filler materials will depend on such factors as the matrix alloy, the process conditions, the reactivity of the molten matrix alloy with the filler material, and the properties sought for the final composite product. For example, when aluminum is the matrix 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. Ceramics which are preferred for use in the present method include alumina and silicon carbide. The size, shape, chemistry and volume percent of the filler material (or preform) can be any that may be required to achieve the properties desired in the composite. Thus, 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. The fibers can be discontinuous (in chopped form) or in the form of continuous filament, such as multifilament tows. Other shapes such as spheres, tubules, pellets, refractory fiber cloth, and the like may be employed. Further, the filler material or preform may be homogeneous or heterogeneous. 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. Further, the constituency of the matrix metal within the metal matrix composite may be modified by controlling the cooling rate of the metal matrix composite. For example, the metal matrix composite may be directionally solidified by any number of techniques including: placing the container holding the metal matrix composite upon a chill plate; and/or selectively placing insulating materials about the container. Such directional solidification can also reduce the size and extent of defects (e.g., porosity). Further, the constituency of the metal matrix may be modified after formation of the metal matrix composite as, for example, by a heat treatment. Moreover, it is possible to use a reservoir of matrix metal to assure complete infiltration of the filler material and/or to supply a second metal which has a different composition from the first source of matrix metal.

It has been observed that for aluminum infiltration and matrix formation around a ceramic filler, 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 body 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 matrix metal. However, as the upper end of the temperature range is approached, nitridation of the metal is more likely to occur.

Thus, 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. For example, the extent of aluminum nitride formation at a given process temperature is believed to increase as the ability of the matrix metal to wet the filler decreases and as the nitrogen concentration of the atmosphere increases.

By the same token, when infiltration enhancer is formed in situ in the permeable mass of filler material prior to infiltration, the amount of aluminum nitride subsequently formed may depend on the amount of magnesium nitride infiltration enhancer formed. As discussed above, the concentration of infiltration enhancer formed may depend on the amount of magnesium infiltration enhancer precursor which can be reacted with nitrogen infiltrating atmosphere. This quantity, in turn, will depend upon the magnesium vapor pressure (temperature dependent) and the amount of time that magnesium is permitted to react with nitrogen.

The following Examples further illustrate the present invention.

EXAMPLE 1

This Example demonstrates an embodiment for making a metal matrix composite body using an interposed sacrificial preform for supplying the molten matrix metal to the object preform. This Example furthermore demonstrates the use of a gating means in conjunction with the sacrificial preform to assist with the recovery of the objective MMC body. The objective preform for the present Example measured about 1 1 inches (279 mm) in diameter by about 2 inches (25 mm) thick was cut from a section of type AL-20B alumina insulating board (Zircar Products, Inc., Florida, NY). This alumina insulating board preform was then bisque fired by heating in an air atmosphere furnace from substantially ambient (e.g., about 20°C) temperature to a temperature of about 900°C at a rate of about 200°C per hour.

After maintaining a temperature of about 900°C for about 6 hours, the furnace and its contents were permitted to cool at the furnace's natural cooling rate.

Next, a sacrificial preform measuring about 12 inches (305 mm) in diameter by about 1 inch (25 mm) thick was prepared. The composition for the sacrificial preform comprised by weight about 2 percent of a liquid inorganic binder component and the balance being solid particulates. The binder component comprised by weight about 2 percent Lupersol 231 peroxide (Aldrich Chemical Co., Milwaukee, WI) and the balance CERASET SN inorganic polymer (Lanxide Corporation, Newark, DE). The solid particulate component comprised by weight about 5 percent magnesium particulate (-50/+100 mesh, Hart Metals, Tamaqua, PA) having substantially all particle diameters between about 150 microns and 300 microns in diameter, and the balance alumina particulate. The alumina particulate component comprised by weight about 1 part 90 grit (216 microns average particle size) 38 Alundum® aluminum oxide (Norton-St. Gobain, Worcester, MA) and about 3 parts 220 grit (66 microns) 38 Alundum® aluminum oxide particulate. The mixing was accomplished as follows: the aluminum oxide and magnesium particulates were hand mixed in a metal can, then transferred to the bowl or mixing chamber of a model RV02 Eirich® high intensity mixer (Eirich Machines, Inc., Uniontown, PA). The binder solution components were stirred together, then about half of the solution was added to the mixing chamber bowl. After mixing on the fast speed setting for a few minutes, the rest of the binder solution was added. After additional mixing, the mixture was screened through a 25 mesh screen (openings of about 710 microns).

The sacrificial preform mixture was then molded into a shape. In particular, about 2.9 kg of the mixture was poured into a mold constructed from cardboard and hand tamped into place. The cardboard mold and its contents was then heated to a temperature of about 150°C to cure the polymeric binder, thereby rendering the sacrificial preform self-supporting. The sacrificial preform was then removed from the cardboard mold.

The sacrificial preform was then lightly fired. Specifically, the preform was placed onto the above-described perforated refractory setter tray and placed into an air atmosphere furnace at about ambient temperature. The furnace and its contents were then heated to a temperature of about 300°C at a rate of about 100°C per hour. After maintaining a temperature of about 300°C for about 8 hours, the temperature was then further increased to a temperature of about 425°C at a rate of about 100°C per hour. After maintaining a temperature of about 425°C for about 8 hours, the temperature was decreased to a temperature of about 50°C at a rate of about 200°C per hour. At a temperature of about 50°C, the refractory setter tray was removed from the furnace.

The sacrificial preform was then coated on all surfaces with a release layer or "gating means". Specifically, the sacrificial preform was first spray coated with Krylon acrylic

(Borden, Inc., Columbus, OH). Then a single layer of Dag 154 colloidal graphite (Acheson Colloids Company, Port Huron, MI) was applied by brush over all surfaces of the sacrificial preform and permitted to dry first in air, then in a drying oven maintained at a temperature of about 80°C. Referring to Figure 3, a graphite boat 31 measuring about 17 inches (432 mm) square by about 4 inches (102 mm) in height was lined on its interior surfaces with a single layer of GRAFOIL® graphite sheet material 33 (Union Carbide Company, Danbury, CT). A substantially non-infiltratable bedding material 35 comprising by weight about 10 percent grade F69 glass frit (Fusion Ceramics, Inc., Carrollton, OH) and the balance 90 grit (216 microns) 38 Alundum® aluminum oxide particulate (Norton-St. Gobain Company) was poured into the graphite sheet lined graphite boat to a depth of about 0.5 inch (13 mm) and leveled. A body of matrix metal measuring about 13 inches ( 330 mm) square and having a mass of about 9.2 kilograms, and comprising by weight about 5 percent magnesium, balance aluminum, was centered in the boat 31 on top of the bedding material admixture 35. Additional bedding material admixture was poured into the boat around the body of matrix metal until the admixture was flush with the top surface of the matrix metal. A PERMAFOIL® graphite foil "window" 39 (TT America, Portland, OR) was centered over the body of matrix metal. Specifically, this graphite foil window was cut such that the foil material extended out to the graphite sheet material lining the graphite boat, and the inside edge defining a circular hole was such that the diameter of the hole was slightly less than the diameter of the sacrificial preform.

Next, a particulate admixture 32 comprising by weight about 5 percent magnesium particulate (-150/+100 mesh, Hart Metals) and the balance 90 grit (216 microns) 38 Alundum® alumina oxide particulate (Norton-St. Gobain) and having a mass of about 226 grams was poured into the opening defined by the graphite foil window 39 and leveled. The sacrificial preform 34 was then centered over this particulate admixture. Additional bedding material admixture 35 was then poured into the graphite foil lined graphite boat around the sacrificial preform almost to the top surface of the sacrificial preform. A layer of magnesium particulate 36 (-50 + 100 mesh, Hart Metals) was applied to the sacrificial preform to a thickness of about 1 mm. The alumina fiberboard preform 38 was centered over the magnesium particulate layer. Excess (e.g., exposed) magnesium particulates were brushed away to complete the setup.

The setup and its contents were then placed into a controlled atmosphere furnace at substantially ambient (e.g., about 20°C) temperature. After sealing the furnace chamber from the ambient atmosphere, the chamber was evacuated and backfilled with commercially pure nitrogen gas. A gas flowrate through the chamber of about 25 SLPM was then established. The furnace and its contents was then increased to a temperature of about 250°C at a rate of about 200°C per hour. After maintaining a temperature of about 250°C for about 12 hours, the temperature was increased to about 425°C, again, at a rate of about 200°C per hour. After maintaining a temperature of about 425°C for about 10 hours, the temperature was increased to about 580°C at a rate of about 100°C per hour. After maintaining a temperature of about 580°C for about 5 hours, the temperature was further increased to about 800°C at a rate of about 100°C per hour. After maintaining a temperature of about 800°C for about 20 hours, the temperature was decreased to about 680°C at a rate of about 200°C per hour. The assembly was removed from the furnace at a temperature of about 680°C and placed on a graphite slab to continue cooling in air to ambient temperature at its natural cooling rate. Disassembly of the graphite boat and its contents revealed that the alumina fiberboard preform had been fully infiltrated to produce a disc-shaped metal matrix composite body. Further, this objective MMC body was easily separated from the infiltrated sacrificial preform using low force mallet impacts.

Thus, the present Example demonstrates that a metal matrix composite body can be formed by infiltrating a low density fiberboard preform through a sacrificial preform featuring a permeable colloidal graphite gating means as a release layer to assist with the recovery of the desired MMC body upon solidification of the matrix metal following infiltration.

EXAMPLE 2

This Example demonstrates an improved technique for infiltrating a preform with a molten matrix metal to form a metal matrix composite article. Specifically, the present Example demonstrates an indirect infiltration technique whereby the preform is not in direct contact with a body of molten matrix metal.

A particulate admixture suitable for compression molding was prepared as follows. The particulate admixture for forming the caliper piston preform consisted of 38 Alundum™ alumina particulate (Norton-St. Gobain, Worcester, MA) having an average particle size of about 25 microns, to which had been added about 2 weight percent of magnesium particulate having substantially all particles smaller than about 45 microns in diameter, plus about 1.5 weight percent of a binder based on polyureasilazane. The binder consisted of CERASET ^M SN polyureasilazane inorganic polymer (Lanxide Corporation, Newark, Delaware) to which had been added about 1% by weight of Lupersol™ 231 peroxide (Aldrich Chemical Co., Milwaukee, WI).

The mixing was accomplished as follows: The alumina and magnesium particulates were hand mixed in a metal can, then transferred to the bowl or mixing chamber of a Model RV02 Eirich® high intensity mixer (Eirich Machines, Inc., Uniontown PA). The binder solution components were stirred together, then about half of the solution was added to the mixing chamber bowl. After mixing on the fast speed setting for a few minutes, the rest of the binder solution was added. After additional mixing, the mixture was screened through a 25 mesh screen and stored in a sealed container until the preforming operation was ready.

A disc-shaped preform was formed by compression molding the above-identified admixture at a temperature of about 170°C, applying a pressure of about 420 psi (2900 kPa) and maintaining this temperature and pressure for about 20 minutes.

The preform was then bisque fired as follows: The piece was placed flush on a setter tray made from refractory material. The setter tray and its contents was then placed into an air atmosphere furnace at about 20°C. The furnace temperature was then raised at a rate of about 100°C per hour to a temperature of about 300°C. After maintaining a temperature of about 300°C for about 2 hours, the furnace temperature was increased to a temperature of about 425°C at about 100°C per hour. After maintaining a temperature of about 425°C for about 4 hours, the furnace temperature was decreased to about 20°C at a rate of about 200°C per hour.

The preform was then removed to a dry box until further processing.

With reference to Figure 4, a graphite boat 61 measuring about 13 inches (330 mm) long by about 9 inches (229 mm) wide by about 3.5 inches (89 mm) in height was lined on its interior surfaces with a single sheet of GRAFOIL® graphite foil material 62 (Union Carbide Co., Danbury, CT). A particulate admixture 63 comprising by weight about 5 percent Grade

F69 glass frit (Fusion Ceramics, Inc., Carrollton, OH) and the balance 90 grit (216 microns ave. particle size) 38 Alundum® alumina particulate (Norton-St. Gobain, Worcester, MA) was poured onto the floor of the graphite foil lined boat 61 to a uniform depth of about 0.5 inch (13 mm). A GRAFOIL® graphite foil ramp 64 and platform 65 were fabricated by cutting and folding another single sheet of graphite foil. The ramp and platform were positioned near one of the interior walls of the graphite foil lined boat. The graphite foil platform measured about 5 inches (127 mm) square by about 0.75 inch (19 mm) in height. A second particulate admixture 66 comprising by weight about 3 percent magnesium particulate (Hart Metals, Tamaqua, PA) having substantially all particles between about 150 microns and about 300 microns in size and the balance 90 grit (216 microns) 38 Alundum® alumina was uniformly distributed over the first particulate admixture 63 and over the graphite foil platform 65 and ramp 64 to a thickness of about 0.25 inch (6 mm). The preform to be infiltrated was then placed on top of this second particulate admixture above the graphite foil platform 65 and an ingot of matrix metal 68 was placed on the second particulate admixture 66 near the wall of the graphite boat opposite that adjacent to the preform. The ingot of matrix metal comprised by weight about 5 percent magnesium, balance aluminum and had a mass of about 460 grams. The opening of the graphite foil lined boat was loosely covered with another sheet of graphite foil 69 to contain the magnesium vapor and complete the setup.

The setup and its contents were then placed into a controlled atmosphere furnace at substantially ambient (e.g., about 20°C) temperature. After sealing the furnace chamber from the ambient atmosphere, the chamber was evacuated and backfilled with commercially pure nitrogen gas. A nitrogen gas flowrate of about 20 slpm was then established. The furnace and its contents were then increased to a temperature of about 250°C at a rate of about 200°C per hour. After maintaining a temperature of about 250°C for up to about 30 hours, the temperature was increased to about 480°C, again, at a rate of about 200°C per hour. After maintaining a temperature of about 480°C for about 5 hours, the temperature was increased to about 580°C. After maintaining a temperature of about 580°C for about 5 hours, the temperature was further increased to about 800°C at a rate of about 100°C per hour. After maintaining a temperature of about 800°C for about 4 hours, the temperature was decreased to about 700°C at a rate of about 200°C per hour. The assembly was removed from the furnace at a temperature of about 700°C and placed on a graphite slab to continue cooling in air to ambient temperature at its natural cooling rate. Disassembly of the graphite boat and its contents revealed that the disc-shaped preform had been fully infiltrated to produce a metal matrix composite body.

Thus, the present Example demonstrates that a metal matrix composite body can be formed by infiltrating a preform with a molten matrix metal even though the preform is not in direct contact with the body of molten matrix metal. The present Example furthermore illustrates that one infiltrated mass of ceramic material (e.g., a metal matrix composite) can be used as a source of matrix metal to infiltrate an adjoining permeable mass or preform.

EXAMPLE 3

This Example demonstrates another embodiment for making a metal matrix composite body using an improved infiltration technique. As in Example 2, the permeable mass or object preform in the present Example is not in direct contact with the body or pool of molten matrix metal. Instead, the present permeable mass or preform is infiltrated through a "sacrificial" metal matrix composite body or layer interposed between and contacting the object preform to be infiltrated and the body of molten matrix metal.

With reference to Figure 5, a particulate admixture 71 comprising by weight about 5 percent Grade F69 glass frit (Fusion Ceramics, Inc., Carrollton, OH) and the balance 90 grit (216 microns ave. particle size) 38 Alundum® alumina (Norton-St. Gobain, Worcester, MA) was poured into a graphite boat 73 measuring about 13 inches (330 mm) long by about 9 inches (229 mm) wide by about 3.5 inches (89 mm) high to a depth of about 0.5 inch (13 mm) and leveled. A graphite foil liner 72 having the approximate inside dimensions as the graphite boat was fabricated from a single sheet of GRAFOIL® graphite foil (Union Carbide Co, Danbury, CT) and positioned over the particulate admixture.

Next, a sacrificial preform 74 was prepared. The composition for the sacrificial preform comprised by weight about 1.5 percent of a liquid inorganic binder component and the balance being solid particulates. The binder component comprised by weight about 1 percent

Lupersol^τ 231 peroxide (Aldrich Chemical Co., Milwaukee, WI) and the balance CERASET SN inorganic polymer (Lanxide Corporation, Newark, DE). The solid particulate component comprised by weight about 2 percent magnesium particulate (-50/+ 100 mesh, Hart Metals, Tamaqua, PA) having substantially all particle diameters between about 150 microns and 300 microns in diameter, and the balance alumina particulate. The alumina particulate component comprised by weight about 1 part 90 grit (216 microns average particle size) 38 Alundum® aluminum oxide (Norton-St. Gobain, Worcester, MA).

The mixing was accomplished as follows: the aluminum oxide and magnesium particulates were hand mixed in a metal can, then transferred to the bowl or mixing chamber of a model RV02 Eirich® high intensity mixer (Eirich Machines, Inc., Uniontown, PA). The binder solution components were stirred together, then about half of the solution was added to the mixing chamber bowl. After mixing on the fast speed setting for a few minutes, the rest of the binder solution was added. After additional mixing, the mixture was screened through a 25 mesh screen (openings of about 710 microns). The sacrificial preform mixture was then molded into a shape. In particular, about 2.9 kg of the mixture was poured into a mold constructed from cardboard and hand tamped into place. The cardboard mold and its contents was then heated to a temperature of about 150°C to cure the polymeric binder, thereby rendering the sacrificial preform self-supporting. The sacrificial preform was then removed from the cardboard mold. The sacrificial preform had a mass of about 500 grams, was slightly larger in diameter than the object preform, but at least twice as thick.

The object preform 77 itself was compression molded at an applied pressure of about 420 psi (2900 kPa), and a cure temperature and time of about 170°C and 10 minutes, respectively. About 350 grams of pressable material produced a tile having a diameter of about 7.5 inches (190 mm) and a thickness of about 0.25 inch (6 mm). This compression moldable powder comprised by weight about 1.5% liquid binder, about 7.5% cellulose and the balance 25 micron (average particle size) alumina powder (Norton-St. Gobain), previously dried at a temperature of about 150°C. Upon molding, the preform had a volumetric loading of alumina of about 45 percent. The binder comprised by weight about 1% Lupersol 231 peroxide (Aldrich Chemical Co., Milwaukee, WI) and the balance CERASET™ SN Inorganic Polymer

(Lanxide Corp., Newark, DE). The object preform was then bisque fired. Specifically, the object preform was placed flat onto a bedding of 36 grit (710 microns particle size) alumina particulate (Norton-St. Gobain, Worcester, MA) supported by a flat refractory plate. The refractory plate and its contents were placed into an air atmosphere furnace and heated to a temperature of about 300°C at a rate of about 100° per hour. After maintaining a temperature of about 300°C for about 4 hours, the temperature was further increased to a temperature of about 1000°C at a rate of about 100°C per hour. After maintaining of about 1000°C for about 4 hours, the temperature was decreased at a rate of about 200°C per hour. Once the furnace had cooled to substantially ambient temperature the refractory plate and its contents were removed and the object preform was stored in a low humidity environment.

A graphite foil "window" or ring 76 having substantially the same outside diameter as the sacrificial preforms and an inside diameter slightly less than the diameter of the objective preform 77 was centered over the sacrificial preforms 74, 75. The objective preform was then centered over the graphite foil window 76, and the stack of preforms was placed adjacent to an interior wall 77 of the graphite foil liner. An ingot of matrix metal 78 weighing about 880 grams and comprising by weight about 7% magnesium, balance aluminum, was placed onto the graphite foil liner in a slightly spaced apart relationship from the stack of preforms.

This completed assembly was then placed into a nitrogen atmosphere furnace (specifically, a tunnel kiln) at substantially ambient temperature (e.g., about 20°C) and slight positive pressure (e.g., just above atmospheric). The furnace and its contents were then heated to a temperature of about 350°C in about 30 minutes. The temperature was then increased to about 425°C in about 40 minutes. From there, the temperature that the setup was exposed to increased to about 650°C in about 15 minutes. Then the temperature was raised to about 800°C in about 100 minutes. The total cycle time through the tunnel kiln was about 24 hours. During this thermal processing, the moisture levels (monitored) were maintained at less than 25 ppm.

Further, within about an hour of achieving a temperature of about 800°C, the oxygen concentration had fallen below 50 ppm to a steady-state level of about 30 ppm. After maintaining a temperature of about 800°C for about 10 hours, the temperature was decreased to a temperature to a temperature of about 700°C. At a temperature of about 700°C the setup was removed from the controlled atmosphere furnace and directionally solidified by using Model

606 "cold guns" (Vortec Corp., Cincinnati, OH) to direct jets of air at the surface of the object preform.

Once the setup had cooled to substantially ambient temperature, the setup was disassembled and a metal matrix composite disc was recovered. Specifically, the disc was easily separated from the graphite foil window and the sacrificial metal matrix composite layers underneath. Examination of the metal matrix composite disc showed complete infiltration. Thus, the present Example demonstrates that a preform can be infiltrated with a molten matrix metal to produce a metal matrix composite article by first feeding the molten matrix metal through one or more intermediate masses, e.g., a sacrificial bed or preform. Infiltration proceeds into the preform from the matrix metal within the sacrificial bed or preform instead of by means of direct contact with the body or pool of molten matrix metal.

EXAMPLE 4

This Example furthermore demonstrates the improved fabrication of a metal matrix composite body through the use of a "sacrificial" MMC body. The techniques used in the present Example to produce an MMC body were substantially the same as those described in

Example 3 with the exception that instead of infiltrating a sacrificial preform to yield a sacrificial MMC, a sacrificial bedding material was infiltrated. Specifically, the sacrificial bedding material had the same composition as the sacrificial preform, except that no binder material such as CER .SET™ SN inorganic polymer was used. Thus, the sacrificial bedding of the present Example was not self-supporting and therefore relied on the body of matrix metal and the walls of the graphite boat for containment and support.

EXAMPLE 5

This Example demonstrates, among other things, a sacrificial MMC layer for assisting in the infiltration of a permeable mass or preform to form a metal matrix composite article and the facilitated recovery thereof.

A preform 85 having a cross section substantially as shown in Figure 6 measuring roughly 6 inches (152 mm) by 6 inches (152 mm) by 4 inches (102 mm) was fabricated by a sedimentation casting process. In particular, a slurry suitable for sedimentation casting was prepared by thoroughly blending about 3 parts by weight solids to 1 part liquid. The liquid component comprised about 5% by weight of Nyacol 2040 colloidal silica (Nyacol Products, Inc., an affiliate of PQ Corporation, Ashland, MA), balance de-ionized water. The solid component comprised by weight about 6% Grade KS44 graphite particulate (Lonza Inc., Fairlawn, NJ) having substantially all particles smaller than about 44 microns in size, and the balance milled, 38 Alundum® fused alumina particulate (Norton-St. Gobain, Worcester, MA) having an average particle size of about 25 microns. The slurry was cast into a rubber mold supported by an aluminum plate placed on a vibration table. As sedimentation proceeded the excess liquid at the top of the casting was first decanted, then daubed with a sponge. After sedimentation was substantially complete, vibration was ceased. The rubber mold and its contents were then frozen to form an inorganic binder network.

After freezing and removal from the rubber mold, the preform was then buried in 90 grit 38 Alundum® alumina (216 microns ave. particle size, Norton-St. Gobain) contained within a refractory boat. The refractory boat and its contents were then dried and fired in an air atmosphere furnace according to the following heating schedule. First, the furnace and its contents was heated from substantially ambient temperature (e.g., about 20°C) to a temperature of about 35°C at a rate of about 100°C per hour. After maintaining a temperature of about 35°C for about 5 hours, the temperature was then further increased to a temperature of about 85°C at a rate of about 50°C per hour. After maintaining a temperature of about 85°C for about 5 hours, the temperature was then further increased to about 1000°C at a rate of about 100°C per hour. After maintaining a temperature of about 1000°C for about 15 hours, the temperature was then decreased to a temperature of about 50°C at a rate of about 200°C per hour. Once the refractory boat and its contents had cooled to a temperature of about 50°C, the boat was removed from the furnace and the preform was recovered and placed into a drying oven pending further processing.

Next, a series of barrier and separation facilitator coatings comprising colloidal graphite were applied to the preform. Specifically, all surfaces of the object preform were coated with DAG 154 colloidal graphite (Acheson Colloids Co., Port Huron, MI) using a foam brush.

After the coating had air dried, those surfaces to be subsequently stucco coated were further brush coated with a slurry comprising equal weight fractions of DAG 154 colloidal graphite and magnesium particulate (Hart Metals, Tamaqua, PA) having substantially all particles between about 150 and 300 microns in size. Those surfaces not being stucco coated were brush coated with Dylon CW colloidal graphite (Dylon Industries, Inc., Cleveland, OH).

Next, a stucco layer 86 comprising an infiltration enhancer precursor material was applied to two large surfaces of the preform. Specifically, the stucco material comprised by weight about 1 percent of a binder, about 3.5 percent of magnesium particulate (Hart Metals) having substantially all particles between about 150 and 300 microns in size and the balance 90 grit (216 microns) alumina particulate (Norton-St. Gobain, Worcester, MA). The binder material comprised by weight about 2 percent Lupersol 231 peroxide (Aldrich Chemical Co., Milwaukee, WI) and the balance CERASET SN inorganic polymer (Lanxide Corp., Newark, DE). This stucco mixture was applied to the outer surfaces of the preform using a tongue depressor to an approximate thickness of about 0.5 inch (13 mm). The stucco coated preform was then placed into an air atmosphere furnace and heated from substantially ambient temperature to a temperature of about 170°C. After maintaining a temperature of about 170°C for about 20 minutes, the temperature was increased to a temperature of about 300°C at a rate of about 100°C per hour. After maintaining a temperature of about 300°C for about 4 hours, the temperature was then further increased to a temperature of about 425°C at a rate of about 100°C per hour. After maintaining a temperature of about 425°C for about 5 hours, the temperature of the furnace and its contents was decreased to substantially ambient temperature at a rate of about 200°C per hour. The coated preform was then removed from the furnace and placed into a graphite boat to prepare a setup for matrix metal infiltration.

The setup of the present Example shared many similarities with the setup described in Example 3. In particular, a particulate bedding material 63 having substantially the same composition as that of Example 3 was placed onto the bottom of a graphite boat 81. A graphite foil box 62 was then placed on top of the particulate bedding material. Next, a sacrificial preform 82 was placed onto the floor of the graphite foil box close to one wall of the box. The sacrificial preform was similar in composition to that used in Example 3 except the sacrificial preform of the present Example comprised by weight about 3 percent magnesium particulate instead of the 2 weight percent magnesium employed in Example 3. A graphite foil "window"

83 was then placed on top of the sacrificial preform. Note that in the present Example there was no 220 grit (66 microns) alumina particulate preform interposed between the sacrificial preform and the graphite foil window. The stucco coated preform 85 was then centered over the opening 87 of the graphite foil window substantially as shown in the figure. An ingot of matrix metal 88 comprising by weight about 7 percent magnesium and the balance aluminum was placed on the floor of the graphite foil box adjacent to the wall opposite that of the preform to complete the setup. The ingot of matrix metal weighed about 1130 grams and the stucco coated preform weighed about 467 grams.

The completed setup was then placed into a controlled atmosphere furnace at substantially ambient temperature. After evacuating the furnace chamber with a mechanical roughing pump and backfilling with commercially pure nitrogen gas, a nitrogen gas flow rate of about 15 standard liters per minute was established and maintained. The setup was then thermally processed substantially according to the furnace schedule used in Example 2 with the exception that the infiltration temperature was about 790°C (as opposed to 800°C in Example 2), and this temperature was maintained for about 21 hours (as opposed to 4 hours in Example

2). On cooling, once the furnace and its contents had stabilized at a temperature of about 700°C, the setup was removed from the furnace and air was directed at the coated preform to bring about directional solidification. Once the setup had cooled substantially to ambient temperature, the setup was disassembled to reveal that matrix metal had infiltrated substantially completely the preform to produce a metal matrix composite article.

EXAMPLE 6

This Example demonstrates, among other things, the use of a sacrificial bedding to form a stress control layer to reduce warping of the objective MMC. Figure 7 is a cross- sectional view (not to scale) of the various materials employed in creating the setup of the present Example. A disc shaped preform measuring about 6.1 inches (155 mm) by about 0.168 inch 94.27 mm) thick was fabricated by injection molding by Certech Inc., Woodridge, NJ. Upon binder removal, the preform comprised by weight about 1 percent silica, about 1.5 percent Grade A-4 clay and the balance 38 Alundum® alumina particulate (25 microns ave. particle size, Norton- St. Gobain, Worcester, MA).

Next, the surfaces not in contact with infiltrating metal were coated with a barrier material. Specifically, and with reference to Figure 7, the barrier comprises a first layer 93 consisting of DAG 161 colloidal graphite (Acheson Colloids Co., Port Huron, MI) deposited at a concentration of about 2.6 mg/cwA. A second layer 95 consisting of Dylon CW colloidal graphite (Dylon Industries, Cleveland, OH) was applied over the first layer at a concentration of about 9.3 mg/cm^. Both layers were applied by a spraying technique. Then, the face of the preform facing the advancing front of infiltrating matrix metal was coated with a release layer 97 consisting of about 3 percent by weight of walnut shell flour, balance DAG 161 colloidal graphite. This release coating was sprayed on at a concentration of about 3.1 mg/cm^. Next, a setup was prepared. First, a sheet of GRAFOIL® graphite foil (Union Carbide

Co., Danbury, CT) was placed on the floor of a graphite boat measuring about 7 inches (178 mm) square on its interior (not shown). About 50 grams of a particulate admixture comprising by weight about 5 percent magnesium particulate (-50 + 100 mesh, Hart Metals, Inc., Tamaqua, PA) and the balance 90 grit (216 microns) 38 Alundum® alumina particulate (Norton-St. Gobain) was poured over the graphite foil and leveled, thereby forming the sacrificial bedding

99. A body of matrix metal 92 measuring about 7 inches (178 mm) square by about 0.25 inch (96 mm) thick and having a mass of about 400 grams and comprising by weight about 7 percent magnesium, balance aluminum was placed onto the sacrificial bedding. The surface of the body of matrix metal facing the disc shaped preform was then coated with a material 94 to help initiate the spontaneous infiltration process. Specifically, this surface was painted with

DAG 154 colloidal graphite (Acheson Colloids Co.). Magnesium particulate (-50 + 100 mesh, Hart Metals Co.) was poured onto the still wet colloidal graphite coating. Inverting the body of matrix metal removed the excess magnesium particulate, leaving approximately a monolayer of such particulate adhered to the colloidal graphite coating. Next, about 38 grams of 220 grit (66 microns) 38 Alundum® alumina particulate

(Norton-St. Gobain) was poured into the graphite boat on top of the coated body of matrix metal and leveled, thereby forming an interlayer 96 between the matrix metal and the preform. The coated preform was placed on top of this alumina particulate interlayer (with the release layer contacting the alumina) to complete the setup. The graphite boat and its contents was then inserted into a controlled atmosphere tunnel kiln for thermal processing. Specifically, the setup was heated from substantially ambient temperature (e.g., about 25°C) to about 350°C in about 30 minutes. The setup was then heated to about 425°C in about 40 minutes, then to about 650°C in another 15 minutes, then to about 800°C in another 100 minutes. The infiltration temperature of about 800°C was maintained for about 123 minutes. The setup thereafter was cooled almost to ambient temperature. The total time in the furnace was about 6.9 hours. During thermal processing, sufficient nitrogen gas was flushed through the furnace such that the steady-state oxygen and moisture concentrations were kept below 35 ppm and 20 ppm, respectively.

Inspection of the thermally processed setup revealed that matrix metal had spontaneously infiltrated the preform to yield a disc shaped MMC body. Matrix metal also had infiltrated the sacrificial bedding and the 220 grit alumina particulate materials yielding a MMC stress control layer and MMC interlayer, respectively. Between these two layers, warpage of the MMC body was held to about 3 to 5 mils (75 to 127 microns) across the disc diameter. In contrast, when these layers are absent from the setup, the warpage of the MMC disc typically is about 10 mils (25 microns) across the diameter.

Thus the present Example demonstrates the utility of infiltrating particulate other than those making up the object preform for purposes of reducing warpage due to thermal expansion rate mismatches.

EXAMPLE 7

The procedures of Example 6 were substantially repeated to produce a disc shaped MMC with the following exception: the barrier material consisted essentially of Dylon CW colloidal graphite (Dylon Industries) applied to the preform at a concentration of about 7.8 mg/cm^.

EXAMPLE 8 This Example demonstrates, among other things, the infiltration of a cup shaped preform according to the techniques of the present invention to produce a metal matrix composite body. In particular, the present Example features a reusable sacrificial ring which assists in accomplishing the infiltration of the object preform. Figure 8 is a cross-sectional schematic view of the setup used to accomplish the infiltration. A cup shaped preform was fabricated by a wax injection molding process as practiced by a commercial vendor (Certech, Inc. Woodridge, NJ). The composition utilized for injection molding comprised by weight about 1 % fumed silica and the balance grade T64 aluminum oxide particulate (-100 mesh, Alcoa Industrial Chemicals Division, Bauxite, Arkansas) having substantially all particles smaller than about 150 microns in size. The cup shaped preform was then bisque fired in an air atmosphere furnace at a maximum temperature of about 1200°C for about 2 hours. This bisque fired preform retained a mass of about 128 grams. Next, a reusable sacrificial preform was prepared. Specifically, a ring having approximately the same diameter and height as the cup shaped preform was wax injection molded (Certech, Inc.) and whose filler material component consisted essentially of grade T64 tabular alumina particulate (-100 mesh, Alcoa). Both the objective and the sacrificial preforms were heated in an air atmosphere furnace to a temperature of about 825°C. After maintaining this temperature of about 825°C for about 2 hours, the preforms were cooled to a temperature of about 150°C at which temperature they were held pending further processing.

Following the air bake, a series of barrier coatings were applied to the sacrificial preform. Specifically, the exterior circumferential surface 104 of the ring shaped preform was brush coated with two layers of undiluted Dylon CW colloidal graphite (Dylon Industries, Cleveland, OH). The surface to be adjacent to the cup shaped preform was brush coated with one layer of undiluted Dag 154 colloidal graphite 106 (Acheson Colloids Company, Port Huron, MI). Next, a setup for matrix metal infiltration was assembled. With reference to Figure 8, the floor or base of a shallow steel boat 101 was covered with several sheets of GRAFOIL® graphite sheet material 103 (Union Carbide Company, Carbon Products Division, Cleveland, Ohio). A cylindrical body of matrix metal 105a having a mass of about 150 grams was centered on the top graphite foil sheet. A second cylindrical body of matrix metal 105b having a mass of about 90 grams was then placed atop the first body. Both cylindrical ingots of matrix metal had a composition comprising by weight about 10.5% magnesium, and the balance aluminum. The sacrificial ring preform 107 was then placed around the cylindrical bodies of matrix metal and adhered to the top graphite foil sheet using RIGIDLOCK® colloidal graphite cement (Polycarbon Corp., Valencia, California). To prevent the formation of a hermetic seal during processing, the sacrificial graphite ring preform featured a vent hole 109 positioned above the highest expected level of molten matrix metal. The cup shaped preform 102 was then placed on top of the sacrificial ring preform and contacting the Dag 154 colloidal graphite coated surface 106. The placement of the cup shaped preform on top of the sacrificial ring preform substantially enclosed the bodies of matrix metal. Finally, a bedding material 108 comprising by weight about 10% grade F69 glass frit (Fusion Ceramics, Carrollton, Ohio) and the balance 90 grit (216 microns) 38 Alundum^ alumina particulate (Norton-St. Gobain, Worcester, MA) was piled up around the base of the sacrificial ring preform to a maximum height of about 0.5 inch (13 mm) to complete the setup.

The setup comprising the steel boat and its contents was then placed into a controlled atmosphere furnace at substantially ambient temperature. After isolating the heating chamber from the ambient atmosphere, the heating chamber was evacuated and backfilled with commercially pure nitrogen gas. A gas flow rate of about 20 standard liters per minutes (slpm) was then established and maintained throughout the subsequent thermal processing. The furnace chamber and its contents was then heated to a temperature of about 250°C. After maintaining a temperature of about 250°C for about 19 hours, the furnace chamber was then heated to a temperature of about 450°C. After maintaining a temperature of about 450°C for about 5 hours, the temperature was further increased to a temperature of about 700°C. After maintaining a temperature of about 700°C for about 2 hours, the temperature was then further increased to a temperature of about 900°C. After maintaining a temperature of about 900°C for about 1 hour, the temperature was decreased to about 800°C. After maintaining a temperature of about 800°C per hour, the temperature was further reduced to about 600°C. Up to this point, the temperature increases and decreases were carried out at a rate of about 200°C per hour. At a temperature of about 600°C, the furnace chamber was opened and the setup was removed and placed onto a Fiberfrax^ insulating ceramic sheet (Carborundum Co., Niagara Falls, NY) and allowed to cool in air at its natural cooling rate. Upon cooling to substantially ambient temperature, the setup was disassembled. Specifically, the cup shaped preform was separated from the rest of the set up using low force impacts. This preform had been completely infiltrated by matrix metal thereby producing a cup shaped MMC body. The sacrificial ring preform had also been completely infiltrated by molten matrix metal during processing to produce a sacrificial MMC body.

This sacrificial MMC body was then prepared for reuse by sandblasting off the adhered colloidal graphite coatings and graphite sheet material. Some carcass of residual matrix metal remain adhered to the interior circumferential surface of this sacrificial MMC body. Fresh coatings of Dag 154 colloidal graphite (Acheson Colloids Company) and Dylon CW colloidal graphite (Dylon Industries) were reapplied to the top and side surfaces of the sacrificial ring shaped MMC body and air baked, as was done previously with the sacrificial ring shaped preform. Another setup was then prepared substantially as described immediately above with the exception that the sacrificial ring shaped preform was now a sacrificial ring shaped MMC body. The subsequent thermal processing for conducting matrix metal infiltration into the cup shaped preform was conducted similarly to the heating schedule used to infiltrate the first cup shaped preform; however, the initial heating was conducted straight to 450°C instead of first stopping at a temperature of about 250°C; further the soak temperature at about 800°C was maintained for only about 6 hours instead of the 10 hour hold for the first infiltration. The cup shaped preform was again completely infiltrated to form a cup shaped MMC body.

Thus, this Example illustrates the in situ production of a sacrificial MMC body through the infiltration of a sacrificial preform which then assists in the delivery of molten matrix metal into the object preform to produce the object MMC body. Further, this Example illustrates the ability to reuse a sacrificial MMC body in a subsequent infiltration of molten matrix metal into a second object preform. The preceding Examples are by no means exhaustive, instead they are illustrative of the present invention. An artisan of ordinary skill will readily appreciate that numerous minor modifications of the above-identified Examples can be made without departing from the scope and spirit of the present invention, as set forth in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A method for making a metal matrix composite body, comprising: providing at least one object preform, body of molten matrix metal, and sacrificial bed or preform; disposing said sacrificial bed or preform between said object preform and said body of molten matrix metal; and causing matrix metal to infiltrate said sacrificial bed or preform and said object preform.

2. A method for making a metal matrix composite body, comprising: providing at least one object preform comprising at least one filler material, body of molten matrix metal, and sacrificial metal matrix composite body; disposing said body of molten matrix metal between said object preform and said sacrificial metal matrix composite body; and causing at least a portion of said body of molten matrix metal to infiltrate said object preform to form an objective metal matrix composite body.

3. The method of claim 1 , wherein said object preform comprises at least one substantially non-reactive filler material comprising a form selected from the group consisting of aggregate, particulates, fibers, spheres and platelets.

4. The method of claim 2, wherein said disposing comprises direct contact of said permeable mass to said matrix metal.

5. The method of claim 2, wherein said disposing comprises indirect contact of said permeable mass to said matrix metal.

6. The method of claim 5, wherein a body is interposed between said permeable mass and said body of matrix metal.

7. The method of claim 6, wherein said body comprises a gating means.

8. The method of claim 1, wherein said body of matrix metal is caused to infiltrate without the requirement for the presence of pressure or vacuum, whether externally applied or internally created.

9. The method of claim 1, further comprising providing an infiltrating atmosphere at least at some point during processing.

10. ^"The method of claim 1, further comprising providing at least one of an infiltration enhancer or infiltration enhancer precursor to at least one of said object preform, said sacrificial bed or preform, and said body of matrix metal.

11. The method of claim 1 , wherein said object preform comprises at least one ceramic material selected from the group consisting of borides, carbides, nitrides and oxides.

12. The method of claim 1, wherein said object preform comprises by volume from about 15 percent to about 90 percent of at least one filler material.

13. The method of claim 12, wherein said at least one filler material comprises a plurality of bodies having an average size ranging from about 1 micron to about 1000 microns.

14. The method of claim 1, wherein said sacrificial bed or preform comprises at least one ceramic material selected from the group consisting of borides, carbides, nitrides and oxides.

15. The method of claim 14, wherein said sacrificial bed or preform comprises an infiltration enhancer precursor material.

16. The method of claim 15, wherein said sacrificial bed or preform comprises a particulate admixture of aluminum oxide and magnesium.

17. The method of claim 1 , wherein an infiltration enhancer precursor material is contacted to at least one surface of said body of matrix metal.

18. The method of claim 2, wherein said matrix metal comprises aluminum.

19. The method of claim 2, wherein said filler material comprises at least one material selected from the group consisting of alumina, magnesium, magnesium alumina and silicon carbide.

20. A method for making a metal matrix composite body, comprising: providing at least one object preform, body of molten matrix metal, and sacrificial bed or preform; disposing said body of molten matrix metal between said object preform and said sacrificial bed or preform; and causing matrix metal to infiltrate said sacrificial bed or preform and said object preform.

21. The method of claim 2, further comprising separating said objective metal matrix composite body from said body of matrix metal.

22. The method of claim 1, wherein said causing matrix metal to infiltrate yields a unitary mass comprising an objective MMC and a sacrificial MMC, said method further comprising detaching said objective MMC from said sacrificial MMC.

23. The method of claim 20, wherein said causing matrix metal to infiltrate yields at least an objective MMC and a sacrificial MMC, said method further comprising separating said objective MMC from said sacrificial MMC.