WO2004018726A1

WO2004018726A1 - Metal matrix composites, and methods for making the same

Info

Publication number: WO2004018726A1
Application number: PCT/US2003/021263
Authority: WO
Inventors: Kamal E. Amin
Original assignee: 3M Innovative Properties Company
Priority date: 2002-08-20
Filing date: 2003-07-08
Publication date: 2004-03-04
Also published as: KR20050058342A; CN1675394A; EP1540025A1; AU2003248844A1; JP2005536355A

Abstract

A metal matrix composite article comprising a first metal and an insert reinforcing the first metal, wherein the first metal selected from the group consisting of aluminium, alloys thereof, and combinations thereof, wherein the insert comprises substantially continuous ceramic oxide fibers and a second metal selected from the group consisting of aluminium, alloys thereof, and combinations thereof, wherein the second metal secures the substantially continuous ceramic oxide fibers in place, wherein the second metal extends along at least a portion of the length of the substantially continuous ceramic oxide fibers, wherein there is an interface layer between the first metal and the insert, and wherein there is an interface layer peak bond strength value between the first metal and the insert of at least 100 MPa. Metal comprising inserts for reinforcing a metal matrix composite article and methods of making t he same. In another aspect, the present invention provides metal matrix composit e articles reinforced with an insert(s) and methods of making the same. Useful m etal matrix composite articles include structural components for aerospace app cations.

Description

METAL MATRIX COMPOSITES, AND METHODS FOR MAKING THE SAME

Field of the Invention

The present invention relates to metal comprising inserts for reinforcing a metal matrix composite article and metal matrix composite articles reinforced with an insert(s).

Description of Related Art

The reinforcement of metal matrices with ceramics is known in the art (see, e.g., U.S. Pat. Nos. 4,705,093 (Ogino), 4,852,630 (Hamajima et al.), 4,932,099 (Corwin et al), 5,199,481 (Corwin et al.), 5,234,080 (Pantale), and 5,394,930 (Kennerknecht), Great Britain Pat. Doc. Nos. 2,182,970 A and B, published May 28, 1987 and September 14,

1988, respectively, and PCT applications having publication nos. WO 02/26658, WO 02/27048, and WO 02/27049, published April 4, 2002). Examples of ceramic materials used for reinforcement include particles, discontinuous fibers (including whiskers) and continuous fibers, as well as ceramic pre-forms. Typically, ceramic material is incorporated into a metal to provide metal matrix composites (MMC) having improved mechanical properties compared to the article made of the metal without the ceramic material. For example, conventional brake calipers for motorized vehicles (e.g., cars and trucks) are typically made of cast iron. To reduce the overall weight of the vehicle, as well as in particular unsprung weight such as brake calipers, there is a desire to use lighter weight parts and/or materials. One technique for aiding in the design of MMCs, including placement of the ceramic oxide material and minimizing the amount of ceramic oxide material needed for the particular application, is finite element analysis.

A brake caliper made of cast aluminum would be about 50% by weight lighter than the same (i.e., the same size and configuration) caliper made of cast iron. The mechanical properties of cast aluminum and cast iron are not the same (e.g., the Young's modulus of cast iron is about 100-170 GPa, while for cast aluminum it is about 70-75 GPa; the yield strength of cast iron is 300-700 MPa, while for cast aluminum it is 200-300 MPa). Hence, for a given size and shape, a brake caliper made from cast aluminum has significantly lower mechanical properties such as bending stiffness and yield strength than the cast iron caliper. Typically, the mechanical properties of such an aluminum brake caliper are unacceptably low as compared to a cast iron brake caliper. A brake caliper made of an aluminum metal matrix composite material (e.g., aluminum reinforced with ceramic fibers) that has the same configuration and at least the same (or better) mechanical properties, such as bending stiffness and yield strength, as a cast iron brake caliper is desirable. One consideration for some MMC articles is the need for post-formation machining (e.g., adding holes or threads, or otherwise cutting away material to provide a desired shape) or other processing (e.g., welding two MMC articles together to make a complex shaped part). Many conventional MMCs typically contain enough ceramic reinforcement material to make machining or welding impractical or even impossible. It is desirable, however, to produce "net-shaped" articles that require little, if any, post- formation machining or processing. Techniques for making "net-shaped" articles are known in the art (see, e.g., U.S. Pat. Nos. 5,234,045 (Cisko) and 5,887,684 (Doll et al.)). In addition, or alternatively, to the extent feasible, the ceramic reinforcement may be reduced or not placed in areas where it may interfere with machining or other processing such as welding.

Another consideration in designing and making MMCs is the cost of the ceramic reinforcement material. The mechanical properties of continuous polycrystalline alpha- alumina fibers such as that marketed by the 3M Company, St. Paul, MN, under the trade designation "NEXTEL 610", are high compared to low density metals such as aluminum. h addition, the cost of ceramic oxide materials such as the polycrystalline alpha-alumina fibers, is substantially more than metals such as aluminum. Hence, it is desirable to minimize the amount of ceramic oxide material used, and to optimize the placement of the ceramic oxide materials in order to maximize the properties imparted by the ceramic oxide materials. Further, it is desirable to provide the ceramic reinforcement material in a package or form that can be relatively easily used to make a metal matrix composite article therefrom.

Although PCT applications having publication nos. WO 02/26658, WO 02/27048, and WO 02/27049, published April 4, 2002 include descriptions of embodiments that address the need for ceramic reinforcement material in a package or form that can be relatively easily used to make a metal matrix composite article therefrom, additional solutions, as well as, and/or alternatively other novel ways of providing metal matrix composite articles, preferably with superior properties to conventional metal matrix composite articles are desired.

Summary of the Invention

In one aspect, the present invention provides a metal matrix composite article comprising a first metal and an insert (in some embodiments at least two, three, or more inserts) reinforcing the first metal, wherein the first metal is selected from the group consisting of aluminum, alloys thereof, and combinations thereof, wherein the insert comprises substantially continuous ceramic oxide fibers and a second metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof, wherein the second metal secures the substantially continuous ceramic oxide fibers in place, wherein the second metal extends along at least a portion of the length of the substantially continuous ceramic oxide fibers, wherein there is an interface layer between the first metal and the insert, and wherein there is an interface layer peak bond strength value between the first metal and the insert of at least 100 MPa (in some embodiments, at least 125 MPa, 150 MPa, 175 MPa, or even at least 200 MPa. In some embodiments, the interface layer is preferably free of oxygen.

L another aspect, the present invention provides in one embodiment a method of making a metal matrix composite article according to the present invention, the method comprising: positioning an insert in a mold, the insert comprising substantially continuous ceramic oxide fibers and first metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof, wherein the first metal secures the substantially continuous ceramic oxide fibers in place, and wherein the first metal extends along at least a portion of the length of the substantially continuous ceramic oxide fibers, the first metal having an outer surface, and a second metal (e.g., Cu, Au, Ni, Ag, Zn, and combinations thereof) on the outer surface of the first metal, and the second metal having a thickness of at least 5 micrometers (in some embodiments, preferably at least 10 micrometers, at least 15 micrometers or even at least 20 micrometers; more preferably, in the range from 5 to 20 micrometers); providing molten third metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof into the mold; cooling the molten third metal to provide an article; and hot isostatic pressing (HIPing) the article to provide metal matrix composite article according to the present invention. Although casting can be conducted in air, in some embodiments, it may be preferable to be conducted in an atmosphere comprising argon (e.g., at least 90% (at least 95%, 99%, or even 100%) by volume Ar, based on the total volume of the atmosphere; typically not greater than 10%, 5%, 1%, or even 0% by volume O₂, based on the total volume of the atmosphere).

In another aspect, the present invention provides a method of making a metal matrix composite article according to the present invention, the method comprising: positioning an insert in a mold, the insert comprising substantially continuous ceramic oxide fibers and first metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof, wherein the first metal secures the substantially continuous ceramic oxide fibers in place, and wherein the first metal extends along at least a portion of the length of the substantially continuous ceramic oxide fibers; providing molten third metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof into the mold, wherein an atmosphere comprising at least 90% (at least 95%, 99%, or even 100%) by volume Ar, based on the total volume of the atmosphere; typically not greater than 10%, 5%, 1%, or even 0% by volume O₂, based on the total volume of the atmosphere) is provided such that providing the molten third metal into the mold is conducted under the atmosphere; and cooling the molten third metal to provide the metal matrix composite article. In some embodiments, the first metal has an outer surface, and a second metal (e.g., Cu, Au, Ni, Ag, Zn, and combinations thereof) on the outer surface of the first metal, wherein the second metal has a thickness of at least 5 micrometers (in some embodiments, preferably at least 10 micrometers, at least 15 micrometers or even at least 20 micrometers; more preferably, in the range from 5 to 20 micrometers). In some embodiments, the method includes hot isostatic pressing (HIPing) after at least partially cooling the molten third metal to provide the metal matrix composite article. In this application:

"peak bond strength value" refers to the peak bond strength value as determined in at least one of Comparative Example A or Example 4, below; "free of oxygen" means no visibly discernable continuous oxide layer at the interface when viewed at 250X with optical microscope as described in the "Oxygen Layer Test" below; and

"substantially continuous ceramic oxide fibers" refers to ceramic oxide fibers having lengths of at least 5 cm. Examples of metal matrix composite articles according to the present invention include structural parts for aerospace applications, brake calipers, high speed rotating rings, and high speed mechanical arms for industrial machinery.

Brief Description of the Drawing FIGS. 1-3 and 5-7 are perspective views of exemplary (metal matrix composite) inserts for making embodiments of metal matrix composite articles according to the present invention.

FIG. 4 is a perspective view of an exemplary metal matrix composite article made from the (metal matrix composite) insert shown in FIG. 3. FIGS. 8 A and 8B are schematic side and top views, respectively, of a sand casting mold assembly used in the working examples.

FIGS. 9 A, 9B, 9C are schematic top, side, end views of a test coupon. FIG. 10 is an optical photomicrograph of a fracture surface of a Comparative Example A metal matrix composite article at about 4X. FIG. 11 is a scanning auger electron (SAM) photomicrograph of a Comparative

Example A metal matrix composite article cross-section. FIG. 12 is a scanning auger electron (SAM) photomicrograph and electron microprobe copper line scan of a Comparative Example A metal matrix composite article cross-section.

FIG. 13 is a scanning auger electron (SAM) photomicrograph of a Comparative Example C metal matrix composite article cross-section.

FIG.14 is a scanning auger electron microprobe oxygen line scan of a Comparative Example C metal matrix composite article cross-section.

FIG. 15 is a photomicrograph of an x-ray radiograph of a Comparative Example C metal matrix composite article. FIG. 16 is a photomicrograph of an x-ray radiograph of an Example 1 metal matrix composite article.

FIG. 17 is an optical photomicrograph of an Example 1 metal matrix composite article cross-section at 20X.

FIG. 18 is a scanning auger electron (SAM) photomicrograph and electron microprobe oxygen line scan of a Example 1 metal matrix composite article cross-section.

FIG. 19 is an optical photomicrograph of a fracture surface of Example 4 metal matrix composite article at about 4X.

FIG. 20 is a scanning auger electron (SAM) photomicrograph and electron microprobe oxygen line scan of a Example 4 metal matrix composite article cross-section.

Detailed Description The present invention provides metal matrix composite articles comprising at least one metal and substantially continuous ceramic oxide fibers. Typically, metal matrix composite articles according to the present invention are designed for the particular application to achieve an optimal, or at least acceptable balance of, desired properties, low cost, and ease of manufacture.

Typically, metal matrix composite articles according to the present invention, such as an insert, are designed for a specific application and/or to have certain properties and/or features. For example, an existing article made of one metal (e.g., steel) is selected to be redesigned to be made from another metal (e.g., aluminum) reinforced with material including substantially continuous ceramic oxide fibers such that the latter (i.e., the metal matrix composite version of the article) has certain desired properties (e.g., Young's modulus, yield strength, and ductility) at least equal to that required for the use of the original article made from the first metal. Optionally, the article may be redesigned to have the same physical dimensions as the original article. The desired metal matrix composite article configuration, desired properties, possible metals and ceramic oxide material from which it may be preferable for it to be made of, as well as relevant properties of those materials are collected and used to provide possible suitable constructions. In some embodiments, a preferred method for generating possible constructions is the use of finite element analysis (FEA), including the use of FEA software run with the aid of a conventional computer system (including the use of a central processing unit (CPU) and input and output devices). Suitable FEA software is commercially available, including that marketed by Ansys, Inc., Canonsburg, PA under the trade designation "ANSYS". FEA assists in modeling the article mathematically and identifying regions where placement of the continuous ceramic oxide fibers, metal(s), and possibly other materials would provide the desired property levels. It is typically necessary to run several iterations of FEA to obtain a more preferred design.

Referring to FIG. 1, an exemplary (metal matrix composite) insert 10 for making a metal matrix composite article according to the present invention comprises substantially continuous (as shown, longitudinally aligned) ceramic oxide fibers 12 and aluminum or alloy thereof 14. In some embodiments, outer surface 15 of aluminum or alloy thereof 14 has first metal (e.g., Cu, Au, Ni, Ag, Zn, and combinations thereof) 16 thereon. Further, in some embodiments, outer surface 17 of second optional metal 18 has second optional metal (e.g., Ni) 18 thereon. The second optional metal is typically used if the first optional metal is Cu and/or Ag. The use of the Ni tends to aid in the adhesion of metal such as Cu and/or Ag to the insert surface.

Referring to FIG. 2, another exemplary (metal matrix composite) insert 10 for making a metal matrix composite article according to the present invention comprises substantially continuous (as shown, longitudinally aligned) ceramic oxide fibers 22 and aluminum or alloy thereof 24. In some embodiments, outer surface 25 of aluminum or alloy thereof 24 has first metal (e.g., Cu, Au, Ni, Ag, Zn, and combinations thereof) 26 thereon. Further, in some embodiments, outer surface 27 of second optional metal 28 has second optional metal (e.g., Ni) 28 thereon.

In some exemplary embodiments of the present invention, the continuous ceramic oxide fibers are substantially longitudinally aligned such that they are generally parallel to each other. While the ceramic oxide fibers may be incorporated into the insert as individual fibers, they are more typically incorporated into the insert as a group of fibers in the form of a bundle or tow. Fibers within the bundle or tow may be maintained in a longitudinally aligned (i.e., generally parallel) relationship with one another. When multiple bundles or tows are utilized, the fiber bundles or tows are also maintained in a longitudinally aligned (i.e., generally parallel) relationship with one another. In some embodiments, it is preferred that all of the continuous ceramic oxide fibers are maintained in an essentially longitudinally aligned configuration where individual fiber alignment is maintained within ± 10°, more preferably ± 5°, most preferably ± 3°, of their average longitudinal axis. For some metal matrix composite articles according to the present invention, it may be preferable or necessary for the ceramic oxide fibers to be curved, as opposed to straight (i.e., do not extend in a planar manner). Hence, for example, the ceramic oxide fibers may be planar throughout the fiber length, non-planar (i.e., curved) throughout the fiber length, or they may be planar at some portions and non-planar (i.e., curved) at other portions. In some embodiments, the substantially continuous ceramic oxide fibers are maintained in a substantially non-intersecting, curvilinear arrangement (i.e., longitudinally aligned) throughout the curved portion of the metal matrix composite article. In some embodiments, the substantially continuous ceramic oxide fibers are maintained in a substantially equidistant relationship with each other throughout the curved portion of the metal matrix composite article.

For example, referring to FIG. 3, an exemplary insert 50 for making a metal matrix composite article according to the present invention comprises substantially continuous (as shown, longitudinally aligned) ceramic oxide fibers 52 and aluminum or alloy thereof 54, wherein substantially continuous ceramic oxide fibers 52 are curved throughout their lengths. In some embodiments, outer surface 55 of aluminum or alloy thereof 54 has first metal (e.g., Cu, Au, Ni, Ag, Zn, and combinations thereof) 56 thereon. Further, in some embodiments, outer surface 57 of second optional metal 58 has second optional metal (e.g., Ni) 58 thereon. An example of a metal matrix composite article which can be made from the latter type of insert is a metal matrix composite ring, such as shown in FIG. 4. Ring 60 comprises aluminum or alloy thereof 54 and ceramic oxide fibers 52 (see Fig. 3). Such rings are useful, for example, in high speed rotating machinery where they are subject to large centrifugal forces.

In another aspect, for some metal matrix composite articles according to the present invention, it may be preferable, or required, to have two, three, four, or more plies of the substantially continuous ceramic oxide fibers (i.e., a ply is at least one layer of substantially continuous ceramic oxide fibers (in some embodiments, preferably at least one layer of tows comprising the substantially continuous ceramic oxide fibers)). The plies may be oriented with respect to each other any of a variety of ways. Examples of the relationships of the plies to each other are shown in FIGS. 5 and 6. Referring to FIG. 5 insert 70 comprises first and second plies of substantially continuous (as shown, longitudinally aligned) ceramic oxide fibers 71 and 72 and aluminum or alloy thereof 74.

In some embodiments, outer surface 75 of aluminum or alloy thereof 74 has first metal (e.g., Cu, Au, Ni, Ag, Zn, and combinations thereof) 76 thereon. Further, in some embodiments, outer surface 77 of second optional metal 78 has second optional metal (e.g., Ni) 78 thereon. First ply of substantially continuous ceramic oxide fibers 71 is positioned 45° with respect to second ply of substantially continuous ceramic oxide fibers 72, although depending on the particular application, the difference in position of a ply with respect to another ply(s) may be anywhere between greater than zero degrees to 90°. Such arrangements of ply may be useful, for example if the metal matrix article is to encounter biaxial and trialaxial loads during use. Optionally, metal matrix composite articles according to the present invention can have two or more plies.

A grouping of fibers may also benefit from being wrapped with substantially continuous ceramic oxide fibers such as shown in FIG. 6, wherein insert 80 comprises substantially continuous (as shown, longitudinally aligned) ceramic oxide fibers 82 spirally wrapped around substantially continuous (as shown, longitudinally aligned) ceramic oxide fibers 81 and aluminum or alloy thereof 84. In some embodiments, outer surface 75 of aluminum or alloy thereof 74 has first metal (e.g., Cu, Au, Ni, Ag, Zn, and combinations thereof) 76 thereon. Further, in some embodiments, outer surface 77 of second optional metal 78 has second optional metal (e.g., Ni) 78 thereon. An example of a metal matrix composite article which may benefit from the properties offered by plies of substantially continuous ceramic oxide fibers include an article that under use is subjected to bending forces about two perpendicular axes.

Typically, the substantially continuous ceramic oxide fibers have lengths of at least 10 cm (frequently at least 15 cm, 20 cm, 25 cm, or more). In some embodiments of the present invention, the substantially continuous ceramic oxide fibers are in the form of tows (i.e., the tows comprise the substantially continuous ceramic oxide fibers). Typically, the substantially continuous ceramic oxide fibers comprising the tow have lengths of at least

10 cm (frequently at least 15 cm, 20 cm, 25 cm, or more).

The ceramic oxide fibers can include, or even consist essentially of, substantially continuous, longitudinally aligned, ceramic oxide fibers, wherein "longitudinally aligned" refers to the generally parallel alignment of the fibers relative to the length of the fibers. In some embodiments, the substantially continuous reinforcing ceramic oxide fibers used to make a metal matrix composite article according to the present invention preferably have an average diameter of at least about 10 micrometers. In some embodiments, the average fiber diameter is no greater than about 200 micrometers, more preferably, no greater than about 100 micrometers. For tows of fibers, in some embodiments, the average fiber diameter is preferably, no greater than about 50 micrometers, more preferably, no greater than about 25 micrometers.

In some embodiments, the substantially continuous ceramic oxide fibers have an average tensile strength of at least about 1.4 GPa, more preferably, at least about 1.7 GPa, even more preferably, at least about 2.1 GPa, and most preferably, at least about 2.8 GPa, although fibers with lower average tensile strengths may also be useful, depending on the particular application.

Continuous ceramic oxide fibers are available commercially as single filaments, or grouped together (e.g., as yarns or tows). Yams or tows may comprise, for example, at least 420 individual fibers per tow, at least 760 individual fibers per tow, at least 2600 individual fibers per tow, or more. Tows are well known in the fiber art and refer to a plurality of (individual) fibers (typically at least 100 fibers, more typically at least 400 fibers) collected in an aligned untwisted form, whereas yarns imply some degree of twist or rope-like construction. Ceramic oxide fibers, including tows of ceramic oxide fibers, are available in a variety of lengths. The fibers may have a cross-sectional shape that is circular or elliptical. Examples of useful ceramic oxide fibers include alpha alumina fibers, aluminosilicate fibers, and aluminoborosilicate fibers. Other useful ceramic oxide fibers may be apparent to those skilled in the art after reviewing the present disclosure.

Methods for making alumina fibers are known in the art and include the method disclosed in U.S. Pat. No. 4,954,462 (Wood et al.). In some embodiments, preferably the alumina fibers are polycrystalline alpha alumina-based fibers and comprise, on a theoretical oxide basis, greater than about 99 percent by weight Al₂O₃ and about 0.2-0.5 percent by weight SiO₂, based on the total weight of the alumina fibers. In another aspect, in some embodiments, preferable polycrystalline, alpha alumina-based fibers comprise alpha alumina having an average grain size of less than 1 micrometer (more preferably, less than 0.5 micrometer). In another aspect, in some embodiments, preferable polycrystalline, alpha alumina-based fibers have an average tensile strength of at least 1.6 GPa (preferably, at least 2.1 GPa, more preferably, at least 2.8 GPa). Alpha alumina fibers are commercially available, for example, under the trade designation "NEXTEL 610" from the 3M Company of St. Paul, MN. Another alpha alumina fiber, which comprises about 89 percent by weight Al₂O₃, amount 10 percent by weight ZrO₂, and about 1 percent by weight Y₂O₃, based on the total weight of the fibers, is commercially available from the 3M Company under the trade designation "NEXTEL 650".

Methods for making aluminosilicate fibers are known in the art and include the method disclosed in U.S. Pat. No. 4,047,965 (Karst et al.). In some embodiments, preferably the aluminosilicate fibers comprise, on a theoretical oxide basis, in the range from about 67 to about 85 percent by weight Al₂O₃ and in the range from about 33 to about 15 percent by weight SiO₂, based on the total weight of the aluminosilicate fibers. In some embodiments, preferable aluminosilicate fibers comprise, on a theoretical oxide basis, in the range from about 67 to about 77 percent by weight Al₂O₃ and in the range from about 33 to about 23 percent by weight SiO₂, based on the total weight of the aluminosilicate fibers. In some embodiments, preferable aluminosilicate fibers comprise, on a theoretical oxide basis, about 85 percent by weight Al₂O₃ and about 15 percent by weight SiO₂, based on the total weight of the aluminosilicate fibers. In some embodiments, preferable aluminosilicate fibers comprise, on a theoretical oxide basis, about 73 percent by weight Al₂O₃ and about 27 percent by weight SiO₂, based on the total weight of the aluminosilicate fibers. Aluminosilicate fibers are commercially available, for example, under the trade designations "NEXTEL 440", "NEXTEL 720", and "NEXTEL 550" from the 3M Company.

Methods for making aluminoborosilicate fibers are known in the art and include the method disclosed in U.S. Pat. No. 3,795,524 (Sowman). In some embodiments, preferably the aluminoborosilicate fibers comprise, on a theoretical oxide basis: about 35 percent by weight to about 75 percent by weight (or even, for example, about 55 percent by weight to about 75 percent by weight) Al₂O₃; greater than 0 percent by weight (or even, for example, at least about 15 percent by weight) and less than about 50 percent by weight (or, for example, less than about 45 percent, or even less than about 44 percent) SiO₂; and greater than about 5 percent by weight (or, for example, less than about 25 percent by weight, less than about 1 percent by weight to about 5 percent by weight, or even less than, about 2 percent by weight to about 20 percent by weight) B₂O₃, based on the total weight of the aluminoborosilicate fibers. Aluminoborosilicate fibers are commercially available, for example, under the trade designation "NEXTEL 312" from the 3M Company. Commercially available substantially continuous ceramic oxide fibers often include an organic sizing material added to the fiber during their manufacture to provide lubricity and to protect the fiber strands during handling. It is believed that the sizing tends to reduce the breakage of fibers, reduces static electricity, and reduces the amount of dust during, for example, conversion to a fabric. The sizing can be removed, for example, by dissolving or burning it away.

It is also within the scope of the present invention to have coatings on the ceramic oxide fibers. Coatings may be used, for example, to enhance the wettability of the fibers, to reduce or prevent reaction between the fibers and molten metal matrix material. Such coatings and techniques for providing such coatings are known in the fiber and metal matrix composite art. The metal cast around an insert may be the same or different than the metal securing the continuous ceramic oxide fibers. Although the aluminum and aluminum alloys used to make, and which comprise, inserts and metal matrix composite articles according to the present invention may contain impurities, in some embodiments it may be preferable to use relatively pure metal (i.e., metal comprising less than 0.1 percent by weight, or even less than 0.05 percent by weight impurities (i.e., less than 0.25 percent 0.1 percent, or even less than 0.05 percent by weight of each of Fe, Si, and/or Mg)). Although higher purity metals tend to be preferred for making higher tensile strength materials, less pure forms of metals are also useful. Suitable aluminum and aluminum alloys are commercially available. For example, aluminum is available under the trade designation "SUPER PURE ALUMINUM; 99.99% Al" from Alcoa of Pittsburgh, PA. Aluminum alloys (e.g., Al-2% by weight Cu (0.03% by weight impurities) can be obtained from Belmont Metals, New York, NY. In some embodiments, examples of preferred aluminum alloys include alloys comprising at least 98 percent by weight Al, aluminum alloy comprises at least 1.5 percent by weight Cu

(e.g., aluminum alloys comprising Cu in the range from 1.5 to 2.5, preferably, 1.8 to 2.2, percent by weight Cu, based on the total weight of the alloy). Useful series of aluminum alloys include 200 (e.g., 201 aluminum alloy, A201.1 aluminum alloy, 201.2 aluminum alloy, 203 aluminum alloy, 206 aluminum alloy, A206.0 aluminum alloy, 224 aluminum alloy, and 224.2 aluminum alloy), 300 (e.g., A319.1 aluminum alloy, 354.1 aluminum alloy, 355.2 aluminum alloy, A356 aluminum alloy, D356 aluminum alloy, A356.1 aluminum alloy, A357 aluminum alloy, and D357 aluminum alloy), 400 (e.g., 413 aluminum alloy, 443 aluminum alloy, 443.2 aluminum alloy, and 444.2 aluminum alloy), 700 (e.g., 713 aluminum alloy and 771 aluminum alloy), 2000 (e.g., 2036 aluminum alloy and 2618 aluminum alloy), 6000 (e.g., 6061 aluminum alloy, 6063 aluminum alloy, 6101 aluminum alloy, 6151 aluminum alloy, and 6201 aluminum alloy), and/or 7000 (e.g., 7072 aluminum alloy) series aluminum alloys.

In some embodiments, examples of preferred aluminum alloys for the insert(s) include alloys comprising at least 98 percent by weight Al, aluminum alloy comprises at least 1.5 percent by weight Cu (e.g., aluminum alloys comprising Cu in the range from 1.5 to 2.5, preferably, 1.8 to 2.2, percent by weight Cu, based on the total weight of the alloy. In some embodiments, preferred aluminum alloys for the insert(s) include 2000 (e.g., 2036 aluminum alloy and 2618 aluminum alloy), 6000 (e.g., 6061 aluminum alloy, 6063 aluminum alloy, 6101 aluminum alloy, 6151 aluminum alloy, and 6201 aluminum alloy), and/or 7000 (e.g., 7072 aluminum alloy) series aluminum alloys. In some embodiments, preferred aluminum alloy cast around the insert(s) include

200 (e.g., 201 aluminum alloy, 203 aluminum alloy, 206 aluminum alloy, and 224 aluminum alloy), 300 (e.g., A356 aluminum alloy, D356 aluminum alloy, A357 aluminum alloy, and D357 aluminum alloy), 400 (e.g., 413 aluminum alloy and 443 aluminum alloy), 700 (e.g., 771 aluminum alloy), and/or 6000 (e.g., 6061 aluminum alloy) series aluminum alloys.

Although thicknesses of metals such as Cu, Au, Ni, Ag, Zn, and combinations thereof outside of specified values may also be useful, if the thickness is too low, the coatings tend to diffuse if the insert is preheated and consequently may not protect the interface from oxidation or otherwise aid in reducing oxidation at the interface, while excess thicknesses tend to interfere with the establishment of a desirable bond strength between the metal of the insert and the metal of the metal matrix composite article. Techniques for depositing metals such as Cu, Au, Ni, Ag, Zn, and combinations thereof are known in the art and include electroplating and vacuum deposition techniques.

Typically thicknesses of the optional Ni are greater than about 1 micrometer, more typically greater than 2 micrometers. In another aspect, typically thicknesses of such metal are less than about 10 micrometers, more typically less than about 5 micrometers. Although thicknesses outside of these values may also be useful, if the thickness is too low, the coatings tend not be as useful in aiding the adhesion of metals such as Cu, Au, Ag, Zn, and combinations thereof to the insert, while excess thicknesses tend to interfere with the establishment of a desirable bond strength between the metal of the insert and the metal of the metal matrix composite. In some embodiments, the Ni is deposited via electroless deposition.

Inserts can be made, for example, by winding a plurality of continuous ceramic oxide fibers (in some embodiments, preferably grouped together (e.g., as yams or tows)) onto a mandrel having the desired dimension and shape for the intended metal insert design. In some embodiments, preferably the fibers being wound are sized. Exemplary sizings include water (in some embodiments, preferably deionized water), wax (e.g., paraffin), and polyvinyl alcohol (PNA). If the sizing is water, the fiber is typically wound onto the mandrel. After winding is completed, the mandrel is removed from the winder and then placed in a refrigerated cooler until the wound fiber freezes. The frozen, wound fiber can be cut as needed. For example, if the fiber is wound around a mandrel made up of four contiguous plates, the rectangular plates can be removed to provide a frozen, fiber preform. The preform can be cut into pieces to provide small preforms. Typically the sizing is removed before it is used to form an insert. The sizing can removed, for example, by placing the formed fiber into a die (in some embodiments, preferably graphite or sand), and then heating the die. The die is used to make an insert.

To form an insert, after the sizing is removed, if present, a die is placed in a can, typically a stainless steel can, preferably open only at one end. The interior of the can in some embodiments is preferably coated with boron nitride or a similar material to protect, minimize reaction between the aluminum/aluminum alloy and the can during the subsequent casting, and/or facilitate release of the metal matrix composite article from the mold. The can with the die within is placed inside the pressure vessel of a pressure casting machine. Subsequently, aluminum and/or aluminum alloy (e.g. pieces of aluminum and/or an aluminum alloy cut from an ingot) is placed on top of the can. The pressure vessel is then evacuated of air and heated above the melting point of the aluminum/aluminum alloy (typically about 50°C to about 120°C above the liquidus temperature). Upon reaching the desired temperature, the heater is turned off and the pressure vessel is then pressurized with typically argon (or a similar inert gas) to a pressure of about 8.5 to about 9.5 MPa, forcing the molten aluminum aluminum alloy to infiltrate the preform. The pressure in the pressure vessel is allowed to decay slowly as the temperature falls. When the article solidifies (i.e., its temperature drops below about 500°C), chamber is vented the cast metal matrix composite article(s) (e.g., insert(s)) is removed from the die(s), and then allowed to further cool in air.

Inserts can also be made, for example, other techniques known in the art, including squeeze casting. For squeeze casting, for example, the formed ceramic oxide fiber can be placed in a die (e.g., a steel die), any sizing present burned away, molten aluminum aluminum alloy introduced into the die cavity, and pressure applied until solidification of the cast article is complete. After cooling, the resulting insert is removed from the die.

The resulting insert can be further processed (e.g., sand blasted and/or surface ground (e.g., with a vertical spindle diamond grinder), for example to remove or reduce oxidation on the surface of the insert. The insert may also be cut as needed to provide a desired shape (including being cut with a water jet). Next, the insert can be coated, if desired with a first metal such as Cu, Au, Ni, Ag, Zn, and combinations thereof. Optionally, a second metal such as Ni is coated onto the insert prior to coating the first metal. Although not wanting to be bound by theory, it is believed that the use of Ni aids in the adhesion of metals such as Cu and Ag onto the insert.

The particular substantially continuous ceramic oxide fibers, matrix material, and process steps for making inserts and/or metal matrix composite articles are selected to provide metal matrix composite articles with the desired properties. For example, the substantially continuous ceramic oxide fibers and metal matrix materials are selected to be sufficiently compatible with each other and the article fabrication process in order to make the desired article. The metal comprising the region of an insert and/or metal matrix composite article according to the present invention in some embodiments is preferably selected such that the metal matrix does not significantly react chemically with the substantially continuous ceramic oxide fibers, (i.e., is relatively chemically inert with respect to the molten metal), for example, to eliminate the need to provide a protective coating on the fiber exterior.

Metal matrix composite articles according to the present invention can be cast with inserts using, in general, techniques known in the art (e.g., gravity casting die casting, and squeeze casting). Finite Element Analysis (FEA) modeling can be used, for example, to identify optimal positions and quantities of the ceramic oxide fiber for meeting desired performance specifications. Such analysis can also be used, for example, to aid in selecting the dimension(s), number, and location, for example of the inserts used. The insert(s) and/or die may be preheated prior to casting. In some embodiments, preferably the insert(s) is preheated to about 500°C-600°C. In some embodiments, preferably the die is preheated to 200°C-500°C. FEA, may also be used, for example, to aid in choosing a casting technique, casting conditions, and/or mold design for casting an insert and/or metal matrix composite article according to the present invention. Suitable FEA software is commercially available, including that marketed by UES, Annapolis, MD, under the trade designation "PROCAST".

For metal matrix composite articles according to the present invention cast in air, the inserts typically include the optional Cu, Au, Ni, Ag, Zn, or combinations thereof. For metal matrix composite articles according to the present mvention cast in an atmosphere comprising, for example, argon, it is generally more favorable to purge the casting atmosphere with the argon one or more times prior to casting.

For metal matrix composite articles having a higher than desired amount of oxidation at the interface between the insert(s) and the metal cast around the insert, the article may be further processed using hot isostatic pressing (HIPing) to break and diffuse the oxide away from the interface and force more complete wetting and/or densification. Techniques for HIPing are well known in the art. Examples of HIPing temperatures, pressures, and times that may be useful for embodiments of the present invention include 500°C to 600°C, 25MPa to 50 MPa, and 4 to 6 hours, respectively. Temperatures, pressures, and times outside of these ranges may also be useful. Lower temperatures tend, for example, to provide less densification and/or increase the HIPing time, whereas higher temperatures may deform the metal matrix composite article. Lower pressures tend, for example, less densification and/or increase the HIPing time, whereas higher pressures tend, for example, to be unnecessary or in some cases, may even damage the metal matrix article. Shorter times tend, for example, to provide less densification, whereas longer times may, for example, be unnecessary. As discussed above, the metal matrix composite articles (including inserts) are typically designed for a certain purpose, and as a result, it is desired to have certain properties, to have a certain configuration, be made of certain materials, etc. Typically, the mold is selected or made to provide the desired shape of the metal matrix composite articles to be cast so as to provide a net shape or near net shape. Net-shaped or near net- shaped articles, can, for example, minimize or eliminate the need for and cost of subsequent machining or other post-casting processing of a cast metal matrix composite articles. Typically, the mold is made or adapted to hold the insert(s) in a desired location(s) such that the substantially continuous ceramic oxide fibers are properly positioned in the resulting metal matrix composite articles. Techniques and materials for making suitable cavities are known to those skilled in the art. The material(s) from which a particular mold (e.g., graphite, steel, and sand) may be made depends, for example, on the metal used to make the metal matrix composite articles.

Other techniques for making metal matrix composite articles may be apparent to those skilled in the art after reviewing the instant disclosure.

Metal matrix composite articles according to the present invention may comprise more than one groupings (e.g., two groupings, three groupings, etc.) of substantially continuous ceramic oxide fibers, wherein a grouping of substantially continuous ceramic oxide fibers is spaced apart from another grouping(s) with the metal secures the substantially continuous ceramic oxide fibers in place there between. For example, referring to FIG. 7, insert 90 comprises groupings 93A, 93B, and 93C of substantially continuous, (as shown, longitudinally aligned) ceramic oxide fibers 92 and aluminum or alloy thereof 94. In some embodiments, outer surface 95 of aluminum or alloy thereof 94 has first metal (e.g., Cu, Au, Ni, Ag, Zn, and combinations thereof) 96 thereon. Further, in some embodiments, outer surface 97 of second optional metal 98 has second optional metal (e.g., Ni) 98 thereon. Metal matrix composite articles according to the present invention may be in any of a variety of shapes, including a rod (including a rod having a circular, rectangular, or square cross-section), an I-beam, L-shape, or a tube. Metal matrix composite articles according to the present invention may be elongated and have a substantially constant cross-sectional area. In some embodiments, inserts and metal matrix composite articles according to the present invention comprise, in the region comprising the substantially continuous ceramic oxide fibers, in the range from about 30 to about 70 percent (in some embodiments, preferably about 35 to about 60 percent, or even about 35 to about 45 percent) by volume metal and in the range from about 70 to about 30 percent (in some embodiments, preferably about 65 to about 40 percent, or even about 65 to about 55 percent) by volume of the substantially continuous ceramic oxide fibers, based on the total volume of the region, hi some embodiments, preferably the inserts and metal matrix composite articles according to the present invention comprise, in the region comprising the substantially continuous ceramic oxide fibers, at least 50 by volume of the substantially continuous ceramic oxide fibers, based on the total volume of the region. In some embodiments, inserts comprise the substantially continuous ceramic oxide fibers, in the range from about 30 to about 70 percent (in some embodiments, preferably about 35 to about 60 percent, or even about 35 to about 45 percent) by volume metal and in the range from about 70 to about 30 percent (in some embodiments, preferably about 65 to about 40 percent, or even about 65 to about 55 percent) by volume substantially continuous ceramic oxide fibers, based on the total volume of the insert, hi some embodiments, preferably the inserts comprise at least 50 by volume of the substantially continuous ceramic oxide fibers, based on the total volume of the insert.

Embodiments of some metal matrix composite articles according to the present invention are free of oxygen at the interface between the insert or holder and the aluminum or aluminum alloy cast around the insert or holder as determined by the following

"Oxygen Layer Test". A portion of a metal matrix composite article is cut to obtain a cross-section of the insert or holder and the aluminum or aluminum alloy cast around the insert or holder. Then cross-section is polished with semi-automatic metallographic grinding/polishing equipment (obtained under the trade name "ABRAMLN" from Struers, Inc, Cleveland, OH). The polishing speed is 150 rpm. The polishing is done in the following successive 6 stages. The polishing force is 150 N, except in Stage 6 it is 250 N: -Stage 1

The sample is polished for 45 seconds using 120 grit silicon carbide paper (obtained from Pace Technologies, Northbrook, IL) while continuously, automatically dripping water onto abrasive pad during polishing. After polishing, the sample is thoroughly rinsed with water. -Stage 2

The sample is polished for 45 seconds using 220 grit silicon carbide paper (obtained from Pace Technologies) while continuously, automatically dripping water onto abrasive pad during polishing. After polishing, the sample is thoroughly rinsed with water. -Stage 3

The sample is polished for 45 seconds using 600 grit silicon carbide paper (obtained from Pace Technologies) while continuously, automatically dripping water onto abrasive pad during polishing. After polishing, the sample is thoroughly rinsed with water.

-Stage 4

The sample is polished for 4.5 minutes using polishing pad (obtained under the trade designation "DP-MOL" from Struers, Inc.), wetted lightly with periodic droplets of lubricant (obtained under the trade designation "PURON, DP- LUBRICANT" from Struers) and sprayed for 1 second with 6 micrometer diamond grit (obtained under the trade designation "DP-SPRAY, P-6 μm" from Stmers). After polishing, the sample is thoroughly rinsed with water. -Stage 5

The sample is polished for 4.5 minutes using polishing pad ("DP-MOL"), wetted lightly with periodic droplets of lubricant (obtained under the trade designation

"PURON, DP-LUBRICANT" from Struers) and sprayed for 1 second with 3 micrometer diamond grit (obtained under the trade designation "DP-SPRAY, P-3 μm" from Stmers). After polishing, the sample is thoroughly rinsed with water. -Stage 6 The sample is polished for 4.5 minutes using a porous synthetic polishing cloth

(obtained under the trade designation "OP-CHEM" from Struers), wetted first with water and colloidal silica suspension (obtained under the trade designation "OP-S SUSPENSION" from Stmers) poured by hand on the cloth. The sample is washed with water during the last 5 seconds of polishing. After polishing, the sample is dried.

The resulting polished sample is viewed at 250X with optical microscope to determine if a visibly discemable continuous oxide layer is present between the insert or holder and the aluminum or aluminum alloy cast around the insert or holder. For reference purposes, Example 3 (see FIG. 10) of copending application having U.S. Serial No. 60/404,672, filed August 20, 2002, when evaluated with this test did not have a visibly discemable continuous oxide layer at the interface, whereas Comparative Example H (see FIG. 11) from the same application did. Referring to FIG. 10, the polished cross-section of Example 3 showed no abrupt boundary at interface 162 between insert matrix 166 and casting alloy 163. Referring to FIG. 11, the polished cross-section of Comparative Example H showed an abrupt boundary, believed to be an oxide layer, at interface 182 between insert matrix 186 and casting alloy 183.

Examples of metal matrix composite articles according to the present invention include brake calipers and aerospace applications (e.g., electrical access doors, reinforcing structural members (e.g., I beams, stiffners, and panels), and landing gears).

This invention is further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be constmed to unduly limit this invention. Narious modifications and alterations of the invention will become apparent to those skilled in the art. All parts and percentages are by weight unless otherwise indicated.

Examples

Comparative Example A

Two aluminum matrix composite articles (Comparative Examples Al and A2) were made as follows. Tows of continuous alpha alumina fibers (available under the trade designation "NEXTEL 610" from the 3M Company, St. Paul, MN; 3,000 denier; Young's modulus of about 370 GPa; average tensile strength of about 3 GPa; average diameter 11 micrometers) were wound using a deionized water sizing, wherein the tows of fiber were dipped fiber in a water bath immediately before being wound onto a four-faced 20.3 cm. (8-inch) square mandrel to produce a fiber preform having a 49.5% volume loading of fiber. The fiber was wound under tension (about 75 grams, as measured by a tension meter (obtained under the trade designation "CERTEN" from Tensitron, Boulder CO) to form rectangular preform plates 8.25 cm (3.25 inches) by 20.3 cm (8 inches) by 0.254 cm (0.1 inch thick). The mandrel was then placed in a cooler to freeze the water and stabilize the resulting preform. When frozen, the edges of the preform were trimmed and the plates were cut into 7.6 cm by 15.2 cm (3 inches by 6 inches) preforms. The resulting 7.6 cm by 15.2 cm by 0.254 cm fiber pre-forms were placed inside a graphite mold, which had been coated with boron nitride. The graphite mold containing the preforms was placed inside a stainless steel can that was open at one end. The can assembly was then placed inside the cylindrical vessel of a conventional gas pressure casting machine. Pieces of aluminum alloy (6061 aluminum alloy obtained from Alcoa of

Pittsburgh, PA ) cut from an ingot were placed on top of the can. The can is placed within pressure vessel designated heating zones to ensure a uniform melt temperature. The pressure vessel is then evacuated of air and heated above the liquidus point of the aluminum alloy (715°C). Upon reaching the desired temperature, the heater was turned off and the pressure vessel pressurized with argon to a pressure of about 9 MPa (1300 psi), forcing the molten aluminum alloy to infiltrate the preforms. The pressure in the pressure vessel was allowed to decay slowly as the temperature falls. When the insert temperature was below about 500 C, the chamber was vented, the can removed from the pressure vessel, and the cast metal matrix composite articles (insert plates) removed from the can and let cool in air.

These insert plates were then sawn lengthwise and milled to form finished inserts having a dimension of 0.9525 cm (0.375 inch) by 15.2 cm (6 inches) by 0.254 cm (0.1 inch).

The surface of the finished insert was sandblasted to clean the surface and remove any oxide layer thereon. The insert was then submerged in a conventional nickel sulfamate plating solution, and a current of 1.5 A applied for 4.5 minutes to deposit a 1 micrometer layer of Ni on the surface of the insert. The insert was then submerged in a conventional copper sulfate plating solution, and a current of 4.4 A applied for 3 minutes to deposit about 5 micrometers of Cu. Four of the copper coated inserts were placed in a sand mold. Referring FIGS. 8 A and 8B, mold 100 is shown in solid lines, and four inserts 101 will be located in the sand mold are shown in phantom lines. Plate 102 which will define the final metal matrix composite article was a right rectangular prism having dimensions of 15.2 cm by 20.3 cm by 2.54 cm. Mold 100 had sprue 104 with 12.5 mm by 19 mm choke 106 feeding tapered runner 108 having a width 63 mm wide. Runner 108 fed four 25.4 mm diameter risers

100, which in turn had 7.6 mm wide blade in-gates 112 emanating from 25.4 mm diameter risers located above mnner 108. The metal matrix composite article was cast in air by pouring molten aluminum alloy D357 at 746 °C (1375°F) into the mold at the sprue. Pouring time was 7 seconds. The inserts were not preheated. To accelerate cooling metal chills were buried into the sand mold. After solidification of the molten aluminum alloy, the resulting metal matrix composite article was removed from the sand mold, and mold waste was cut away from the article.

One of the four resulting metal matrix composite articles was bent until broken to provide a cross-sectional fracture surface, which is shown in FIG. 10.

One of the four resulting metal matrix composite articles was cross-sectioned, cut to about 10 cm size, mounted in epoxy, and polished as follows using semi-automatic metallographic grinding/polishing equipment (obtained under the trade name "ABRAMIN" from Stmers, Inc, Cleveland, OH). The polishing speed was 150 rpm. The polishing was done in the following successive 6 stages. The polishing force was 150 N, except in Stage 6 it was 250 N: -Stage 1

The sample was polished for 45 seconds using 120 grit silicon carbide paper (obtained from Pace Technologies, Northbrook, IL) while continuously, automatically dripping water onto abrasive pad during polishing. After polishing, the sample was thoroughly rinsed with water. -Stage 2

The sample was polished for 45 seconds using 220 grit silicon carbide paper (obtained from Pace Technologies) while continuously, automatically dripping water onto abrasive pad during polishing. After polishing, the sample was thoroughly rinsed with water. -Stage 3

The sample was polished for 45 seconds using 600 grit silicon carbide paper (obtained from Pace Technologies) while continuously, automatically dripping water onto abrasive pad during polishing. After polishing, the sample was thoroughly rinsed with water. -Stage 4

The sample was polished for 4.5 minutes using polishing pad (obtained under the trade designation "DP-MOL" from Stmers, Inc.), wetted lightly with periodic droplets of lubricant (obtained under the trade designation "PURON, DP- LUBRICANT" from Stmers) and sprayed for 1 second with 6 micrometer diamond grit (obtained under the trade designation "DP-SPRAY, P-6 μm" from Stmers). After polishing, the sample was thoroughly rinsed with water. -Stage 5

The sample was polished for 4.5 minutes using polishing pad ("DP-MOL"), wetted lightly with periodic droplets of lubricant (obtained under the trade designation

"PURON, DP-LUBRICANT" from Stmers) and sprayed for 1 second with 3 micrometer diamond grit (obtained under the trade designation "DP-SPRAY, P-3 μm" from Stmers). After polishing, the sample was thoroughly rinsed with water. -Stage 6 The sample was polished for 4.5 minutes using a porous synthetic polishing cloth

(obtained under the trade designation "OP-CHEM" from Stmers), wetted first with water and colloidal silica suspension (obtained under the trade designation "OP-S SUSPENSION" from Stmers) poured by hand on the cloth. The sample was washed with water during the last 5 seconds of polishing. After polishing, the sample was dried.

The polished cross-section was coated with few angstroms gold layer via sputtering gold thereon. The resulting sample was viewed in a scanning auger electron (SAM) microscope (obtained under the trade designation SAM 600" from Physical Electronics Company (previously know as Perkins Elmer), Eden Prairie, MN). Referring to FIG. 11, the SAM photomicrograph shows insert 111, interface 112, and cast aluminum alloy 113.

Further, an electron microprobe copper line scan was conducted in a line across the insert, interface and cast aluminum alloy. The results are shown in FIG. 12, wherein 121 is the insert, 122 is the interface, 123 is the cast aluminum alloy, and the copper line scan is 124. One of the four resulting metal matrix composite articles was slit with a diamond saw into four portions, each having one insert therein to form test coupons. Each portion was then milled to a finished test coupon 130 as illustrated in FIGS. 9 A, 9B, and 9C, wherein the insert is designated with reference numeral 135, and wherein dimension dl was 5.08 cm (2 inches), dimension d2 was 2.54 cm (1 inch), dimension d3 was 0.25 cm (0.1 inch), d4 was 1 cm (0.4 inch), d5 was 0.9525 cm (0.375 inch), and d6 was nominally 0.254 cm (0.1 inch) but was actually measured on each sample to determine the area of the interface area carrying the load ("Interface Area") (illustrated with reference letter "Z" on the FIGS. 9 A, 9B, and 9C. The test coupon was then placed in a universal testing machine (obtained from Instron Corporation in Canton, MA; Model 8500-133). More specifically, the test coupon was clamped into the lower jaws of the testing machine. About 10 MPa (1.5 Ksi)) hydraulic pressure was applied (using a foot pedal connected servo) to move the jaw to clamp the test coupon. The upper cross-head was then lowered and the test coupon clamped by the upper jaw, again using about 10 MPa of pressure. Care was taken to ensure good alignment of the loading axis with the test coupon bond plane. The test coupon was pulled at a rate of 0.017 mm/sec, and both displacement and load ("Load") were recorded up to the point of complete separation of the interface. The Peak Bond Strength was determined by dividing the maximum "Load" by the "Interface Area". The results for Examples la and lb are shown in Table 1, below.

Table 1

revealed significant segregation at the interface, that may have been caused by contamination of the materials used to make the article.

Comparative Example B

Three other metal matrix composite articles (i.e., Comparative Examples Bl, B2, and B3) were prepared as described in Example 1, except the copper plating was conducted for 8 minutes, and the resulting Cu coating was about 20 micrometers thick. The bond strength for each of Comparative Examples B 1, B2, and B3are provided in the Table 1, above, along with the thickness of the Cu.

Comparative Example C Four Comparative Example A (i.e., Comparative Examples CI, C2, C3, and C4) metal matrix composite articles was prepared as described in Comparative Example A, except the inserts were not sandblasted and no Ni or Cu coating was provided. The bond strength for each of Comparative Examples CI, C2, C3, and C4 are provided in the Table 1, above. One of the four resulting metal matrix composite articles was cross-section and polished and viewed in a SAM as described in Comparative Example A. Referring to FIG. 13, the SAM photomicrograph shows insert 131, interface 132, and cast aluminum alloy 133. Further, an electron microprobe oxygen line scan was conducted in a line across the insert 131, interface 132, and cast aluminum alloy 133 is shown in FIG. 14 wherein 145 is the oxygen line scan. A sharp oxide peak (believed to be aluminum oxide) about 3 micrometers wide was believed to have inhibited bonding between the insert and the cast aluminum alloy.

One of the four resulting metal matrix composite articles was placed in a conventional x-ray radiography machine. The article was placed on a turntable inside the machine chamber and centered to be positioned in the path of the x- ray beam. Unexposed x-ray film (medium speed film obtained from Eastman Kodak Company, Rochester, NY), inside a protective frame, was placed behind the article. The x- ray source was turned on and the article exposed to 90 KV at 3.5 amps for about 3 to 5 minutes (ASTM Standard E- 94-88, was followed to provide a film density of about 3. The exposed film was processed using conventional technique. A print is shown in FIG. 15, wherein 151 is the insert and 153 is the cast aluminum alloy. Debonding between insert 151 and cast aluminum alloy 153 is clearly seen. Example 1

Eight Example 1 (i.e., Examples la, lb, lc, Id, le, If, lg, and lh) metal matrix composite articles was prepared as described in Comparative Example A, except no Ni or Cu coating was provided, and the mold was purged with argon gas (i.e., argon was flowed through the mold for about 15 minutes). The bond strength for each of Examples la, lb, lc, Id, le, If, lg, and lh are provided in the Table 1, above.

One of the four resulting metal matrix composite articles was x-rayed as described in Comparative Example C. Referring To FIG. 16, wherein 161 is the insert and 163 is the cast aluminum alloy. Contrasting with FIG. 15, no interface debonding was seen in FIG. 16, indicating complete bonding between inset 161 and cast aluminum alloy 163.

One of the four resulting metal matrix composite articles was cross-section and polished as described in Comparative Example A. The polished cross-section was coated with few angstroms of gold as described in Comparative Example A. The resulting sample was viewed in a scanning electron microscope (SEM) (obtained from Physical Electronics, Eden Prairie, MN; Model 600). Referring to FIG. 17, the optical photomicrograph shows insert 171 and cast aluminum alloy 173.

One of the four resulting metal matrix composite articles was cross-section and polished and viewed in a SAM as described in Comparative Example A. Further, an electron microprobe oxygen line scan was conducted in a line across the insert, interface and cast aluminum alloy. Referring to FIG. 18, the SAM photomicrograph shows insert 181, interface 182, cast aluminum alloy 183, and oxygen line scan 185.

Example 2

Two metal matrix composite articles (i.e., Examples 2a and 2b) were prepared as described in Comparative Example A, except the articles were further processed by hot isostatic pressing. The articles were hot isostatically pressed in argon at a temperature of about 1010 °F (543 °C) and a pressure of about 34.5 MPa (5.0 Ksi) for about 4 hours. The bond strength for each of Examples 2a and 2b are provided in the Table 1, above, along with the thickness of the Cu. Example 3

Two metal matrix composite articles (i.e., Examples 3a and 3b) were prepared as described in Example 2, except the articles were further processed by hot isostatic pressing as described in Example 3. The bond strength for each of Examples 3a and 3b are provided in the Table, above, along with the thickness of the Cu.

One of the four resulting metal matrix composite articles was bent until broken to provide a cross-sectional fracture surface, which is shown in FIG. 19.

Example 4 Eight metal matrix composite articles (i.e., Examples 4a, 4b, 4c, 4d, 4e, 4f, 4g, and

4h) were prepared as described in Example 3 and tested as described in Comparative Example A, except that the test coupons machined from these articles had a thickness in the d4 dimension of 5 mm (0.2 inch). The Peak bond strength for each of Examples 4a, 4b, 4c, 4d, 4e, 4f, 4g, and 4h are provided in Table 2, below, along with the thickness of the Cu.

One of the four resulting metal matrix composite articles was cross-section and polished and viewed in a SAM as described in Comparative Example A. Further, an electron microprobe oxygen line scan was conducted in a line across the insert, interface and cast aluminum alloy. Referring to FIG. 20, the SAM photomicrograph shows insert 201, interface 202, cast aluminum alloy 203, and oxygen line scan 205.

Table 2

Narious modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth herein.

Claims

What is claimed is:

1. A metal matrix composite article comprising a first metal and an insert reinforcing the first metal, wherein the first metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof, wherein the insert comprises substantially continuous ceramic oxide fibers and a second metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof, wherein the second metal secures the substantially continuous ceramic oxide fibers in place, wherein the second metal extends along at least a portion of the length of the substantially continuous ceramic oxide fibers, wherein there is an interface layer between the first metal and the insert, and wherein there is an interface layer peak bond strength value between the first metal and the insert of at least 100 MPa.

2. The metal matrix composite article according to claim 1 wherein the substantially continuous ceramic oxide fibers are longitudinally aligned.

3. The metal matrix composite article according to claim 1 wherein the interface layer peak bond strength value between the first metal and the insert is at least 150 MPa.

4. The metal matrix composite article according to claim 1 wherein the interface layer peak bond strength value between the first metal and the insert is at least 150 MPa as determined in Comparative Example A.

5. The metal matrix composite article according to claim 1 wherein the interface layer peak bond strength value between the first metal and the insert is at least 150 MPa as determined in Example 4.

6. The metal matrix composite article according to claim 1 wherein the interface layer peak bond strength value between the first metal and the insert is at least

200 MPa.

7. The metal matrix composite article according to claim 1 wherein the interface layer peak bond strength value between the first metal and the insert is at least 200 MPa as determined in Comparative Example A.

8. The metal matrix composite article according to claim 1 wherein the interface layer peak bond strength value between the first metal and the insert is at least 200 MPa as determined in Example 4.

9. The metal matrix composite article according to claim 1 wherein the substantially continuous ceramic oxide fibers are polycrystalline alpha alumina fibers.

10. The metal matrix composite article according to claim 9 wherein the polycrystalline alpha alumina fibers have an average tensile strength of at least 2.8 GPa, wherein the polycrystalline alpha alumina fibers comprise, on a theoretical oxide basis, greater than about 99 percent by weight Al₂O and about 0.2-0.5 percent by weight SiO₂, based on the total weight of the alumina fibers, and wherein alpha alumina present in the polycrystalline alpha alumina fibers has an average grain size of less than 1 micrometer.

11. The metal matrix composite article according to claim 9 wherein the alpha alumina fibers comprise at least 50 percent by volume of the total volume of the metal matrix article.

12. The metal matrix composite article according to claim 1 wherein the substantially continuous ceramic oxide fibers comprise at least 50 percent by volume of the total volume of the metal matrix article.

13. The metal matrix composite article according to claim 1 wherein the first metal is an aluminum alloy comprises at least 1.5 percent by weight Cu, based on the total weight of the aluminum alloy.

14. The metal matrix composite article according to claim 1 wherein the first metal is an aluminum alloy comprising in the range from 1.5 to 2.5 percent by weight Cu, based on the total weight of the aluminum alloy.

15. The metal matrix composite article according to claim 1 wherein the first metal is an aluminum alloy comprising in the range from 1.8 to 2.2 percent by weight Cu, based on the total weight of the aluminum alloy.

16. The metal matrix composite article according to claim 1 wherein the first metal is 6061 aluminum alloy.

17. The metal matrix composite article according to claim 16 wherein the second metal is one of a 200, 300, 400, or 700 series aluminum alloy.

18. A method of making a metal matrix composite article, the method comprising: positioning an insert in a mold, the insert comprising substantially continuous ceramic oxide fibers and first metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof, wherein the first metal secures the substantially continuous ceramic oxide fibers in place, and wherein the first metal extends along at least a portion of the length of the substantially continuous ceramic oxide fibers, the first metal having an outer surface, and Cu on the outer surface of the first metal, and the second metal having a thickness of at least 5 micrometers; providing molten third metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof into the mold; cooling the molten third metal to provide an article; and hot isostatically pressing the article to provide the metal matrix composite article according to claim 1.

19. The method according to claim 18 wherein the second metal has a thickness of at least 15 micrometers.

20. The method according to claim 18 wherein the second metal has a thickness of at least 20 micrometers.

21. A method of making a metal matrix composite article, the method comprising: positioning an insert in a mold, the insert comprising substantially continuous ceramic oxide fibers and first metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof, wherein the first metal secures the substantially continuous ceramic oxide fibers in place, and wherein the first metal extends along at least a portion of the length of the substantially continuous ceramic oxide fibers; providing molten third metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof into the mold, wherein an atmosphere comprising at least 90% by volume Ar and not greater than 10% by volume O₂, based on the total volume of the atmosphere, is provided such that providing the molten third metal into the mold is conducted under the atmosphere; and cooling the molten third metal to provide the metal matrix composite article according to claim 1.

22. The method according to claim 21 wherein the substantially continuous ceramic oxide fibers are polycrystalline alpha alumina fibers.

23. The method according to claim 22 wherein the polycrystalline alpha alumina fibers have an average tensile strength of at least 2.8 GPa, wherein the polycrystalline alpha alumina fibers comprise, on a theoretical oxide basis, greater than about 99 percent by weight Al₂O₃ and about 0.2-0.5 percent by weight SiO₂, based on the total weight of the alumina fibers, and wherein alpha alumina present in the polycrystalline alpha alumina fibers has an average grain size of less than 1 micrometer.

24. The method according to claim 22 wherein the alpha alumina fibers comprise at least 50 percent by volume of the total volume of the metal matrix article.

25. The method according to claim 21 wherein the third metal is an aluminum alloy comprising in the range from 1.5 to 2.5 percent by weight Cu, based on the total weight of the aluminum alloy.

26. The method according to claim 21 wherein the third metal is an 6061 aluminum alloy.

27. A method of making a metal matrix composite article, the method comprising: positioning an insert in a mold, the insert comprising substantially continuous ceramic oxide fibers and first metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof, wherein the first metal secures the substantially continuous ceramic oxide fibers in place, and wherein the first metal extends along at least a portion of the length of the substantially continuous ceramic oxide fibers,; providing molten third metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof into the mold, wherein an atmosphere comprising at least 90% by volume Ar and not greater than 10% by volume O₂, based on the total volume of the atmosphere, is provided such that providing the molten third metal into the mold is conducted under the atmosphere; cooling the molten third metal to provide an article; and hot isostatically pressing the article to provide the metal matrix composite article according to claim 1.