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.

In 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 inserts for reinforcing a metal matrix composite article and methods of making the same. In another aspect, the present invention provides metal matrix composite articles reinforced with an insert (s) (e. g. , one, two, three, four, five, six, or more inserts) and methods of making the same.

Embodiments of metal matrix composite articles according to the present invention for use as inserts for reinforcing metal matrix composite articles according to the present invention that include at least 8 micrometers (in some embodiments, preferably at least 10 micrometers, at least 12 micrometers, or even at least 15 micrometers; more preferably, in the range from 12 to 15 micrometers) of metal having a positive Gibbs oxidation free energy above at least 200°C (e. g. , silver, gold, alloys thereof, and combinations thereof).

Such embodiments typically can provide metal matrix composite articles having very desirable bonding between the insert (s) and the metal of the metal matrix composite article comprising the insert (s) (e. g. , in some embodiments, preferably a bond interface free of oxygen and/or a peak bond strength value of at least 100 MPa (in some embodiments, preferably at least 125 MPa, at least 150 MPa, at least 175, or even at least 180 MPa)).

Although not wanting to be bound by theory, it is believed that the presence of metal having a positive Gibbs oxidation free energy above at least 200°C aids in facilitating obtaining the bonding between the insert (s) and the metal of the metal matrix composite article comprising the insert (s). Further, although not wanting to be bound by theory, it is

believed that the presence of metal having a positive Gibbs oxidation free energy above at least 200°C aids in facilitating absence of oxygen at the interface between the insert (s) and the metal of the metal matrix composite article comprising the insert (s).

In one embodiment, the present invention provides a first metal matrix composite article (e. g. , an insert for reinforcing a metal matrix composite article) comprising: substantially continuous ceramic oxide fibers and first metal selected from the group consisting of aluminum, alloys thereof (e. g. , a 200,300, 400,700, and/or 6000 series (in some embodiments, preferably a 200 series) aluminum alloy), 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 on the outer surface of the first metal, the second metal having a positive Gibbs oxidation free energy above at least 200°C (e. g., silver, gold, alloys thereof, and combinations thereof), and the second metal having a thickness of at least 8 micrometers (in some embodiments, preferably at least 10 micrometers, at least 12 micrometers, or even at least 15 micrometers; more preferably, in the range from 12 to 15 micrometers; in another aspect, typically less than 20 micrometers).

Optionally, the first metal matrix composite article further comprises a third metal (e. g., Ni) between the second metal and the outer surface of the first metal.

In another aspect, the present invention provides a method of making the first metal matrix composite article according to the present invention, the method comprising: securing substantially continuous ceramic oxide fibers in a first metal selected from the group consisting of aluminum, alloys thereof (e. g. , a 200,300, 400,700, and/or 6000 series (in some embodiments, preferably a 200 series) aluminum alloy), and combinations thereof, such that 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 providing a second metal on the outer surface of the first metal to provide the metal matrix composite article, the second metal having a positive Gibbs oxidation free energy above at least 200°C (e. g. , silver, gold, alloys thereof, and combinations thereof).

In one preferred embodiment of the first metal matrix article according to the present invention, the present invention provides a second metal matrix composite article (e. g. , an insert for reinforcing a metal matrix composite article) comprising: substantially continuous ceramic oxide fibers and metal selected from the group consisting of aluminum, alloys thereof (e. g. , a 200,300, 400,700, and/or 6000 series (in some embodiments, preferably a 200 series) aluminum alloy), and combinations thereof, wherein the metal secures the substantially continuous ceramic oxide fibers in place, and wherein the metal extends along at least a portion of the length of the substantially continuous ceramic oxide fibers, the metal having an outer surface; Ni on the outer surface of the metal, the Ni having an outer surface; and Ag on the outer surface of the Ni, the Ag having a thickness of at least 8 micrometers (in some embodiments, preferably 10 micrometers, 12 micrometers, or even 15 micrometers; more preferably, in the range from 12 to 15 micrometers; in another aspect, typically less than 20 micrometers).

In another aspect, the present invention provides a method of making the second metal matrix composite article according to the present invention, the method comprising: securing substantially continuous ceramic oxide fibers in a metal selected from the group consisting of aluminum, alloys thereof, and combinations thereof, such that the metal extends along at least a portion of the length of the substantially continuous ceramic oxide fibers, the metal having an outer surface; and providing Ni on the outer surface of the metal, the Ni having an outer surface; and providing Ag on the outer surface of the Ni, to provide the metal matrix composite article.

In one embodiment, the present invention provides a third metal matrix composite article comprising a first metal and an insert reinforcing the first metal, wherein the first metal is selected from the group consisting of aluminum, alloys thereof (e. g. , a 200,300, 400,700, and/or 6000 series (in some embodiments, preferably a 300 or 400 series) aluminum alloy), 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 (e. g. , a 200,300, 400,700, and/or 6000 series (in some embodiments, preferably a 200 series) aluminum alloy), 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, preferably at least 125 MPa, at least 150 MPa, at least 175, or even at least 180 MPa). In some embodiments, preferably the interface layer is free of oxygen. In another aspect, the interface layer may include an average amount of a metal having a positive Gibbs oxidation free energy above at least 200°C (e. g. , silver, gold, alloys thereof, and combinations thereof), and wherein the average amount of such metal is (e. g. , at least 15, 20,25, 30,35, 40,45, or even, 50 percent by weight) higher in the interface layer than in the first metal. In another aspect, the interface layer may include an average amount of Ag and Ni (e. g. , at least 15,20, 25,30, 35,40, 45, or even, 50 percent by weight of each Ag and Ni) higher than that present in the first metal. In another aspect, the first and second metals each have a melting point, wherein the melting point of the second metal is at least 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, or even 50°C higher than the melting point of the first metal. In another aspect, the first metal and second metals may be different (e. g. , aluminum and an aluminum alloy, or different aluminum alloys).

Optional, the third metal matrix composite article comprises two, three, four, five, six, or more inserts. Optionally, the inserts have the same or different composition, or some inserts have the same composition, and others different compositions.

In another aspect, the present invention provides a method of making the third 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 (e. g. , a 200,300, 400,700, and/or 6000 series (in some embodiments, preferably a 200 series) aluminum alloy), 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 on the outer surface of the first metal, the second metal having a positive Gibbs oxidation free energy above at least 200°C (e. g. , silver, gold, alloys thereof, and combinations thereof) ; providing molten third metal selected from the group consisting of aluminum, alloys thereof (e. g. , a 200,300, 400,700, and/or 6000 series (in some embodiments, preferably, a 300 or 400 series) aluminum alloy), and combinations thereof into the mold; and cooling the molten third metal to provide the metal matrix composite article.

In another aspect, the present invention provides a method of making a preferred embodiment of the third 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 (e. g. , a 200,300, 400,700, and/or 6000 series (in some embodiments, preferably a 200 series) aluminum alloy), 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 Ni on the outer surface of the first metal, the Ni having an outer surface, and Ag on the outer surface of the Ni; providing molten second metal selected from the group consisting of aluminum, alloys thereof (e. g. , a 200,300, 400,700, and/or 6000 series (in some embodiments, preferably a 300 or 400 series) aluminum alloy), and combinations thereof into the mold; and cooling the molten second metal to provide the metal matrix composite article.

In another aspect, the present invention provides a method for making a metal matrix composite insert for making a metal matrix composite article, the method comprising :

designing a metal matrix composite article to comprise a metal matrix composite reinforcement insert, the insert to comprise: substantially continuous ceramic oxide fibers and first metal selected from the group consisting of aluminum, alloys thereof (e. g. , a 200, 300,400, 700, and/or 6000 series (in some embodiments, preferably a 200 series) aluminum alloy), 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; and preparing, based on the resulting design, a metal matrix composite reinforcement insert comprising: the substantially continuous ceramic oxide fibers and the 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 further comprising: a second metal on the outer surface of the first metal, the second metal having a positive Gibbs oxidation free energy above at least 200°C (e. g. , silver, gold, alloys thereof, and combinations thereof), and the second metal having a thickness of at least 8 micrometers (in some embodiments, preferably 10 micrometers, 12 micrometers, or even 15 micrometers; more preferably, in the range from 12 to 15 micrometers; in another aspect, typically less than 20 micrometers).

In another aspect, the present invention provides a method for making a metal matrix composite insert for making a metal matrix composite article, the method comprising : designing a metal matrix composite article to comprise a metal matrix composite reinforcement insert, the insert to comprise:

substantially continuous ceramic oxide fibers and metal selected from the group consisting of aluminum, alloys thereof (e. g. , a 200, 300,400, 700, and/or 6000 series (in some embodiments, preferably a 200 series) aluminum alloy), and combinations thereof, wherein the first metal secures the substantially continuous ceramic oxide fibers in place, and wherein the metal extends along at least a portion of the length of the substantially continuous ceramic oxide fibers; and preparing, based on the resulting design, a metal matrix composite reinforcement insert comprising: the substantially continuous ceramic oxide fibers and the 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 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 further comprising: Ni on the outer surface of the metal, the Ni having an outer surface; and Ag on the outer surface of the Ni, the Ni having a thickness of at least 8 micrometers (in some embodiments, preferably 10 micrometers, 12 micrometers, or even 15 micrometers; more preferably, in the range from 12 to 15 micrometers; in another aspect, typically less than 20 micrometers).

Surprisingly, embodiments of methods according to the present invention can be used to make metal matrix composite articles wherein the molten metal in the mold is in the molten state for less than 75 seconds (in some embodiments, preferably less than 60 seconds). By contrast, conventional methods tend to require the molten metal in the mold to be in the molten state for 200 seconds or more. Although not wanting to be bound by theory, it is believed that the presence of metal having a positive Gibbs oxidation free energy above at least 200°C enables formation of a bond between the insert and the metal of the metal matrix composite article (in some embodiments, preferably without an oxide layer at the interface) and hence does not require an extended period of heating of the

interface by molten aluminum or aluminum alloy, as applicable to attempt to break up the oxide layer to achieve metallurgical bonding.

In this application: "a positive Gibbs oxidation free energy above at least 200°C"refers to the quantity AGrxn = AHrxn-TASrxn where AH°rxn is the enthalpy of the oxidation reaction in kJ/mol, T is the temperature in degrees Kelvin, and AS°rXn is the entropy of the oxidation reaction (in kJ/mol°K) remaining positive for temperatures greater than 200° C (473° K) ; "peak bond strength value"refers to the peak bond strength value as determined by the"Peak Bond Strength"test described below; "free of oxygen"means no visibly discernable continuous oxide layer at the interface when viewed at 250X with optical microscope as described in Example 3; and "substantially continuous ceramic oxide fibers"refers to ceramic oxide fibers having lengths of at least 5 cm.

First and second metal matrix composite articles according to the present invention are useful, for example, to provide reinforcement material in metal matrix composite articles. One advantage of an aspect of the present invention is that it allows for an existing article made of (original) metal (e. g. , cast iron) to be redesigned to be made from another metal (e. g. , aluminum) reinforced with substantially continuous 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 original metal. Optionally, the article may be redesigned to have the same physical dimensions as the original article.

Examples of third metal matrix articles according to the present invention include brake calipers, high speed rotating rings, and high speed mechanical arms for industrial machinery.

Brief Description of the Drawing FIG. 1 is a perspective view of an exemplary metal matrix composite article according to the present invention.

FIG. 2 is a perspective view of another exemplary metal matrix composite article according to the present invention.

FIGS. 3A and 3B are perspective views of another exemplary metal matrix composite article according to the present invention.

FIGS. 4A and 4B are perspective views of a brake caliper according to the present invention.

FIGS. 4C and 4D are cross-sectional views of the brake caliper shown in FIGS. 4A and 4B.

FIG. 5 is a perspective view of another exemplary metal matrix composite article according to the present invention.

FIG. 6 is a perspective view of a metal matrix composite article made from the metal matrix composite article shown in FIG. 5.

FIG. 7 is a perspective view of another exemplary metal matrix composite article according to the present invention utilizing multiple plies of ceramic oxide fibers wherein the longitudinal axes of the plies are positioned at an angle greater than zero relative to one another.

FIG. 8 is a perspective view of a grouping of substantially continuous ceramic oxide fibers spirally wrapped around another group of substantially continuous ceramic oxide fibers.

FIG. 9 is a perspective view of another exemplary metal matrix composite article according to the present invention.

FIGS. 10A and 10B are plan views of another brake caliper according to the present invention.

FIG. 11 is a perspective view of another brake caliper according to the present invention.

FIG. 12 is an optical photomicrograph of a polished cross-section of an Example 1 insert.

FIG. 13 is a schematic of a die cavity used to make the metal matrix composite article of Example 1 made using the inserts described in Example 1.

FIG. 14 is a schematic of the compressive shear test equipment used to determine the peak bond strength value between an insert and the metal of a metal matrix composite article according to the present invention made using an insert according to the present invention.

FIG. 15 is a plot of the insert displacement under load for Examples 3 and 7.

FIG. 16 is an optical photomicrograph of a polished cross-section of an Example 3 metal matrix composite article.

FIG. 17 is an optical photomicrograph of a polished cross-section of a Comparative Example H metal matrix composite article.

FIG. 18 is a photomicrograph of a test sample as described in Example 1.

FIG. 19 is a perspective view of an exemplary insert holder.

FIG. 19A is a cutaway view of a portion of FIG. 19.

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. , cast iron) 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, exemplary first metal matrix composite article according to the present invention (which in some embodiments is also an exemplary second metal matrix composite article according to the present invention) 10 comprises substantially continuous (as shown, longitudinally aligned) ceramic oxide fibers 12, aluminum or alloy thereof 14, outer surface 15, metal having a positive Gibbs oxidation free energy above at least 200°C 16, optional additional metal (e. g. , Ni) 18, and outer surface 17 of optional metal 18. Metal matrix composite article 10 is useful for making metal matrix composite articles according to the present invention, wherein the additional metal of the latter articles can be the same or different than aluminum or alloy thereof 14.

Referring to FIG. 2, exemplary first metal matrix composite article according to the present invention (which in some embodiments is also an exemplary second metal matrix composite article according to the present invention) 20 comprises substantially continuous (as shown, longitudinally aligned) ceramic oxide fibers 22, aluminum or alloy thereof 24, outer surface 25, metal having a positive Gibbs oxidation free energy above at least 200°C 26, optional additional metal (e. g. , Ni) 28, and outer surface 27 of optional metal 28. Metal matrix composite article 20 is useful for making metal matrix composite articles according to the present invention, wherein the additional metal of the latter articles can be the same or different than aluminum or alloy thereof 24.

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 first metal matrix composite article (or, in some embodiments also a second metal matrix composite article) according to the present invention as individual fibers, they are more typically incorporated into the first metal matrix composite article (or, in some embodiments also a second metal matrix composite article) 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, FIGS. 3A and 3B are other first exemplary metal matrix composite articles according to the present invention (which in some embodiments is also an exemplary second metal matrix composite articles according to the present invention) (inserts) 30 of FIGS. 4A, 4B, 4C, and 4D, wherein metal matrix composite articles (inserts) 30 comprises substantially continuous (as shown, longitudinally aligned) ceramic oxide fibers 32, aluminum or alloy thereof 34, outer surface 35, metal having a positive Gibbs oxidation free energy above at least 200°C 36, optional additional metal (e. g. , Ni) 38, and outer surface 37 of optional metal 38. Substantially continuous ceramic oxide fibers 32 are substantially planar between section lines BB and CC and between section lines DD and EE, and curved between section lines CC and DD. Alternatively, the longitudinally aligned, substantially continuous ceramic oxide fibers may be non-planar throughout their lengths.

For example, referring to FIG. 5, another first exemplary metal matrix composite article according to the present invention (which in some embodiments is also an

exemplary second metal matrix composite article according to the present invention) (insert) 50 comprises substantially continuous (as shown, longitudinally aligned) ceramic oxide fibers 52, aluminum or alloy thereof 54, outer surface 55, metal having a positive Gibbs oxidation free energy above at least 200°C 56, optional additional metal (e. g. , Ni) 58, and outer surface 57 of optional metal 58, wherein substantially continuous ceramic oxide fibers 52 are curved throughout their lengths. 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. 6. Ring 60 comprises aluminum or alloy thereof 54 and ceramic oxide fibers 52 (see Fig. 5). 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. 7 and 8. Referring to FIG. 7 exemplary first metal matrix composite article according to the present invention (which in some embodiments is also an exemplary second metal matrix composite article according to the present invention) (insert) 70 comprises first and second plies of substantially continuous (as shown, longitudinally aligned) ceramic oxide fibers 71 and 72, aluminum or alloy thereof 74, outer surface 75, metal having a positive Gibbs oxidation free energy above at least 200°C 76, and optional additional metal (e. g. , Ni) 78 and outer surface 77 of optional metal 78. 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°.

In some embodiments, preferred positioning of a ply with respect to another ply (s) for some applications may be in the range from about 30° to about 60°, or even, for example, in the range from about 40° to about 50°. 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. 8, wherein metal matrix composite article (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, aluminum or alloy thereof 84, outer surface 85, metal having a positive Gibbs oxidation free energy above at least 200°C 86, and optional additional metal (e. g. , Ni) 88 and outer surface 87 of optional metal 88. 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 metal matrix composite articles according to the present invention preferably have an average diameter of at least about 5 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 a Young's modulus of greater than about 70 GPa, more preferably, at least 100 GPa, at least 150 GPa, at least 200 GPa, at least 250 GPa, at least 300 GPa, or even at least 350 GPa.

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 yams or tows). Yarns 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 yams 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 A1203 and about 0.2-0. 5 percent by weight Si02, 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 A1203, amount 10 percent by weight ZrO2, and about 1 percent by weight Y203, 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 A1203 and in the range from about 33 to about 15 percent by weight Si02, 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 A1203 and in the range from about 33 to about 23 percent by weight Si02, 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 A1203 and about 15 percent by weight Si02, 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 A1203 and about 27 percent by weight Si02, 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) A1203 ; 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) Si02 ; 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) B203, 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.

For third metal matrix composite articles according to the present invention, the aluminum or aluminum alloy of the insert and aluminum or aluminum alloy of the third metal matrix composite article are typically different, but can be the same. Although the aluminum and aluminum alloys used to make, and which comprise, metal matrix composite articles according to the present invention (including inserts) 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 by weight, 0.1 percent by weight, 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), and 200 (e. g. , A201.1 aluminum alloy, 201.2 aluminum alloy, A206.0 aluminum alloy, and 224.2 aluminum alloy), 300 (e. g. , A319.1 aluminum alloy, 354.1 aluminum alloy, 355.2 aluminum alloy, and A356.1 aluminum alloy), and/or 400 (e. g. , 443.2 aluminum alloy and 444.2 aluminum alloy), 700 (e. g. , 713 aluminum alloy), and 6000 (e. g. , 6061 aluminum alloy) series aluminum alloys.

Although thicknesses of the metal having a positive Gibbs oxidation free energy above at least 200°C outside of specified values may also be useful, if the thickness is too low, the coatings tend to diffuse when 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 metal having a positive Gibbs oxidation free energy above at least 200°C are known in the art and include electroplating.

Typically, thicknesses of the optional Ni are greater than about 1 micrometer, more typically greater than 2 micrometers, or even greater than 3 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 the metal having a positive Gibbs oxidation free energy above at least 200°C 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.

First or second metal matrix composite articles (inserts) according to the present invention 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 (PVA). 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 a metal matrix composite article (insert). The sizing can removed, for example, by placing the formed fiber into a die (in some

embodiments, preferably graphite), and then heating the die. The die is used to make the metal matrix composite article (e. g. , insert).

To form the metal matrix composite article (e. g. , 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 80°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 and 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.

Metal matrix composite articles (e. g. , insert) can also be made, for example, by 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 metal matrix composite article (e. g. , 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 metal matrix composite article (e. g. , insert) is coated with metal having a positive Gibbs oxidation free energy

above at least 200°C. Optionally, a metal such as Ni is coated onto the metal matrix composite article (e. g. , insert) prior to coating the metal having a positive Gibbs oxidation free energy above at least 200°C. The use of the Ni tends to aid in the adhesion of metal such as Ag to the insert.

The particular substantially continuous ceramic oxide fibers, matrix material, and process steps for making 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 a metal matrix composite 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.

Third metal matrix composite articles according to the present invention can be cast using inserts according to the present invention using, in general, techniques known in the art (e. g. , squeeze casting and permanent tool gravity 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. Typically, the insert (s) and/or die is preheated prior to casting. Although not wanting to be bound by theory, it is believed that preheating the insert (s) facilitates desirable metallurgical bonding between the insert (s) and the aluminum and/or aluminum alloy of the third metal matrix composite articles. 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. Although casting can typically be conducted in air, it is also within the scope of the present invention to cast in other atmospheres (e. g. , argon).

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 'TROCART".

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 may be made depends, for example, on the metal used to make the metal matrix composite articles. Commonly used mold materials include graphite or steel.

Optionally, an insert holder (s) is used to hold an insert (s) according to the present invention. Such insert holders can help facilitate placement of an insert (s) in the mold, which in turn facilitates placement of the insert (s) in the resulting metal matrix composite article. In one exemplary embodiment, the insert holder includes at least one portion for securing at least one insert, wherein the insert holder comprises a first metal selected from the group consisting of aluminum, alloys thereof (e. g. , a 200,300, 400,700, and/or 6000 series (in some embodiments, preferably a 6000 series) aluminum alloy), and combinations thereof. In some embodiments, the insert holder has an outer surface, and a second metal on the outer surface of the first metal having a positive Gibbs oxidation free energy above at least 200°C, wherein the second metal has a thickness of at least 8 micrometers (in some embodiments, preferably 10 micrometers, 12 micrometers, or even 15 micrometers; more preferably, in the range from 12 to 15 micrometers; in another aspect, typically less than 20 micrometers).

An exemplary holder with inserts positioned therein is shown in FIGS. 19 and 19A.

Referring to FIG. 19, article 10 comprises holder 191 portions 192A, 192B, 192C, and 192D for securing inserts according to the present invention 193A, 193B, and 193C.

Referring to FIG. 19A, holder 191 comprises aluminum and/or alloy (s) thereof 194, outer surface 195, optional metal having a positive Gibbs oxidation free energy above at least 200'C 197, and optional additional metal (e. g. , Ni) 196 and outer surface 198 of optional metal 196.

For additional details on exemplary insert holders see copending application having U. S. Serial No. 60/404,729, filed August 20,2002.

Again, surprisingly, embodiments of first or second metal matrix composite articles (inserts) according to the present invention can be used to make metal matrix composite articles wherein the molten metal in the mold is in the molten state for less than 75 seconds (in some embodiments, preferably less than 60 seconds). Although longer times for keeping the molten metal in the mold in the molten state may also be useful, the shorter times (i. e. , less than 75 seconds), and although not wanting to be bound by theory, it is believed that the longer times may lead to deformation of the insert.-In some embodiments, preferably the insert does not significantly deform during the casting of a third metal matrix composite article according to the present invention (i. e. , the insert has a first outer dimensional configuration (i. e. , size and shape) prior to casting, and a second outer dimensional shape after casting, wherein the first and second outer dimensional configurations are the same, and wherein it is understood that the metal having a positive Gibbs oxidation free energy above at least 200°C and optional metal such as Ni tend to diffuse into the metal of the casting metal (and possibly the metal of the insert)).

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 reduce or remove the undesired oxidation. HIPing may also be used to reduce the porosity, if any, in the metal matrix composite article. 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, to provide 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.

For additional details on exemplary inserts and techniques for making metal matrix composite articles see copending application having U. S. Serial No. 60/404, 704, filed August 20,2002.

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 securing the substantially continuous ceramic oxide fibers in place there between. For example, referring to FIG. 9 first metal matrix composite article according to the present invention (which in some embodiments is also an exemplary second metal matrix composite article according to the present invention) (insert) 90 comprises groupings 93A, 93B, and 93C of substantially continuous, (as shown, longitudinally aligned) ceramic oxide fibers 92, aluminum or alloy thereof 94, outer surface 95, metal having a positive Gibbs oxidation free energy above at least 200°C 96, and optional additional metal (e. g. , Ni) 98 and outer surface 97 of optional metal 98.

Embodiments of some metal matrix composite articles according to the present invention have a"Peak Bond Strength Value"between the insert or holder, as applicable (i. e. , depending on which one is being tested), and the aluminum or aluminum alloy cast around the insert as determined by the following"Peak Bond Strength Value Test"of at least 100 MPa (in some embodiments, preferably at least 125 MPa, at least 150 MPa, at least 175, or even at least 180 MPa). A schematic of the compressive shear test equipment is shown in FIG. 9, wherein compressive shear test equipment 140 includes pushout tool 141, test sample 142, support block 143, and 100,000 Newton (22,482 pounds) compressive load cell 147. The metal matrix composite to be tested is cross-sectioned perpendicular to the longitudinal axis of the insert or holder, as applicable; the thickness of

the cross-section for the insert is 1.16 cm (0.46 inch), the thickness of the cross-section for the holder is 0.4 cm, and the diameter of either 2.5 cm (1 inch).

Pushout tool 141 has a corresponding cross-section at the point of contact with insert or holder, as applicable, 144 with test sample 142, except the cross-sectional area of pushout tool 141 is 10 percent less (i. e. , the shape of the cross-section of pushout tool 141 and insert or holder, as applicable, 144 is the same, but the size of the cross-section of pushout tool 144 is less). Pushout tool 141 is clamped in upper jaws 145 of the hydraulic chuck with a hydraulic pressure of 10.34 MPa (1500 pounds per square inch). Support block 143 has a 2.54 cm (1.0 inch) diameter by 0.15 cm (0.06 inch) deep counterbore. A 1.1 cm (0. 435 inch) diameter through hole is placed on top of the open jaws 145 of the bottom of hydraulic chuck 146.

Sample to be tested 142 is placed on top of support block 143 and nested in the counterbore for centering of the insert or holder, as applicable, over the through hole.

Bottom 148 of hydraulic chuck support 146 is raised until the gap between the upper pushout tool 141, and the insert or holder, as applicable, to be pushed out (i. e. , sample to be tested 144), is 0.025 cm. (0.01 inch). The exposed insert or holder, as applicable, in the test specimen is then visually positioned with the matching tip of pushout tool 141 by manually sliding support block 143 horizontally and rotationally until the cross-sections of the two elements match.

The test is then conducted by moving the lower hydraulic support chuck up toward fixed pushout tool 141 at a rate of 0.05 cm (0.020 inch) per minute while simultaneously monitoring the load and deflection. The insert or holder, as applicable, is thereby brought into contact with the fixed pushout tool face and the contact force between the two recorded as a function of displacement. The test is discontinued shortly after the peak force is reached and a total deflection of about 0.05 cm (0.020 inch) is obtained.

After completion of the test, the specimen is examined under an optical microscope at 100X magnification to verify that the test insert or holder, as applicable, and pushout tip were properly aligned such that their cross-sections were overlapping.

The average shear stress is calculated using the following formula: Average Shear Stress = Load at first slippage, N lbs.) Area of contact between insert and aluminum alloy, m2 (in2).

The loads are plotted as a function of the insert displacement. The load at which the pushout curve has a discontinuity (i. e. , where there is initial slippage at the interface between the insert or holder and the aluminum or aluminum alloy cast around the insert or holder, as applicable) is a peak bond strength value.

The Peak Bond Strength is calculated using Finite Element Analysis (FEA). Finite Element Analysis (FEA) software (available under the trade designation"ANSYS"from Ansys Inc. , Canonsburg, PA) is used to model the insert or holder, as applicable, and show that the ratio of peak bond strength to measured average shear stress is approximately 3.0.

The FEA calculation is done as follows. A finite element model of the test specimen geometry is created. The insert or holder, as applicable, is meshed with elements of dimension 0.02 cm by 0.02 cm by 0.05 cm (0.01 inch by 0.01 inch by 0.02 inch) cubes, except at the top of the insert or holder, as applicable, where the mesh size is 0.02 cm in all dimensions. The aluminum/aluminum alloy cast around the insert or holder, as applicable, is meshed with cubes having sides of 0.05 cm (0.02 inch) near the insert or holder, as applicable, and 0.10 cm (0.04 inch) elsewhere in the modeled test specimen. The FEA software computes the shear stress at points along the surface of the insert or holder, as applicable, for an applied pressure of 533.3 MPa (corresponding to a pushout test load of 2900 pounds). The calculation determines that the peak shear stress across all points of the surface of the insert or holder, as applicable, and the average across the insert surface or holder surface, as applicable. The ratio of Peak Bond Strength to average shear stress is thus about 3 to 1.

Metal matrix composite articles (including the first and second 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 (including the first and second metal matrix composite articles) according to the present invention may be elongated and have a substantially constant cross-sectional area.

One preferred use for some embodiments of first and/or second metal matrix composite articles according to the present invention is as reinforcement in an aluminum or an alloy thereof matrix composite article. An example of such a metal matrix composite article is shown in FIGS. 4A, 4B, 4C, and 4D. Brake caliper 40 for a motor vehicle (e. g. , a car, sport utility vehicle, van, or truck, comprises aluminum or alloy thereof 42, and metal matrix composite articles (inserts) according to the present invention 30 (see FIG. 3) that incorporates substantially continuous (as shown longitudinally aligned) ceramic oxide fibers 48. FIGS. 4C and 4D are cross-sectional views of FIG. 4B along lines FF and GG, respectively. In FIG. 4C and 4D, brake caliper 40 comprises aluminum or alloy thereof 42 and metal matrix composite articles (inserts) according to the present invention 30.

Another exemplary construction of a brake caliper incorporating a first and/or metal matrix composite article (s) according to the present invention, as well as a brake system for a motor vehicle (e. g. , a car, sports utility vehicle, van, or truck utilizing the brake caliper, is shown in FIG. 10A and 10B. An example of a disk brake for a motor vehicle comprises a rotor; inner and outer brake pads disposed on opposite sides of the rotor and movable into braking engagement therewith; a piston for urging the inner brake pad against the rotor; and a brake caliper comprising a body member having a cylinder positioned on one side of the rotor and containing the piston, an arm member positioned on the other side of the rotor and supporting the outer brake pad, and a bridge extending between the body member and the arm member across the plane of the rotor.

Referring again to FIGS. 10A and 10B, disc brake assembly 100 comprises brake caliper housing 101 formed of body member 102, arm member 104, and bridge 106 connected at one end to body member 102 and at other end to arm member 104. Body member 102 has a generally cylindrical recess 103 therein which slideably receives piston 105 to which is pressed inner brake pad 107. Inner face 195 of arm member 104 supports outer brake pad 109 which faces inner brake pad 107. Brake rotor 196, connected to a wheel (not shown) of a vehicle, lies between inner and outer brake pads 107,109, respectively. Inserts 200 comprise aluminum or alloy thereof 204. Interfaces 209 between inserts 200 and aluminum or alloy thereof 208 wherein the average amount of metal

having a positive Gibbs oxidation free energy above at least 200°C (optionally additional metal (e. g. , Ni) ) is higher in interface 209 than in aluminum or alloy thereof 208.

Hydraulic, or other, actuation of piston 105 causes inner brake pad 107 to be urged against one side of rotor 196 and, by reactive force, causes caliper housing 101 to float, thereby bringing outer brake pad 109 into engagement with the other side of rotor 196, as is well known in the art.

Another exemplary brake caliper according to the present invention is shown in FIG. 11, wherein brake caliper 110 comprises aluminum and/or alloy thereof 111 and insert 10.

Examples of disc brakes for using metal matrix composite brake calipers according to the present invention incorporating first metal matrix composite articles according to the present invention include fixed, floating and sliding types. Additionally details regarding brake calipers and brake systems can be found, for example, in U. S. Pat. Nos. 4,705, 093 (Ogino) and 5,234, 080 (Pantale).

Other examples of metal matrix composite articles according to the present invention which can be made from first and/or second metal matrix composite articles according to the present invention include automotive components (e. g. , automotive control arms and automotive wrist pins) and gun components (such as barrel support for rifled steel liner).

In some embodiments, metal matrix composite articles according to the present invention (i. e. , first and/or second metal matrix composite articles according to the present invention, as well as third metal matrix composite articles according to the present invention made from a first and/or second metal matrix composite article (s) according to the present invention) comprise, in the region comprising the substantially continuous ceramic oxide fibers, in the range from about 70 to about 30 percent (in some embodiments, preferably about 60 to about 35 percent, or even about 45 to about 35 percent) by volume metal and in the range from about 30 to about 70 percent (in some embodiments, preferably about 40 to about 65 percent, or even about 55 to about 65 percent) by volume of the substantially continuous ceramic oxide fibers, based on the total volume of the region. In some embodiments, preferably the metal matrix composite articles according to the present invention (i. e. , first and/or second metal matrix composite

articles according to the present invention, as well as third metal matrix composite articles according to the present invention made from a first and/or second metal matrix composite article (s) 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. In 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.

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 construed to unduly limit this invention. Various 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 Example 1 Two aluminum matrix composite inserts according to the present invention 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 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 65% 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

four rectangular preform plates (10.2 cm (4 inches) by 20.3 cm (8 inches) by 0.29 cm (0.115 inch) thick). The mandrel was then placed in a-40°C (-40°F) cooler to freeze the water and stabilize the resulting preform. When frozen, the plates were cut into 7.6 cm by 15.2 cm (3 inch by 6 inch) preforms.

A graphite die assembly (obtained from Schunk Graphite Technology, Inc., Menomonie Falls, WI) was used to cast the aluminum matrix composite plates. The width of the graphite die was 9.64 cm, the length 15.24 cm and the height 4.90 cm. The die included four slots for inserts with 0.89 cm center-to-center spacing between the slots.

The graphite die assembly was coated with an aqueous graphite particle dispersion (obtained under the trade designation"AQUADAG"from Acheson Colloids Company, Port Huron, MI). Four of the frozen 7.6 cm by 15.2 cm preforms were placed in the graphite die assembly, one preform in each of the four cavities. The die assembly with the preforms positioned therein was then placed in an oven at 120°C (250°F) for about 16 hours until the water in the preforms evaporated.

The die assembly was then placed in a stainless steel can (length 102 mm, width 53 mm, and height 500 mm) open at one end, and having its interior coated with a boron nitride suspension (obtained under the trade designation"RS 1000"from ZYP Coatings Inc., Oak Ridge, TN). Although not wanting to be bound by theory, it is believed that the boron nitride coating inhibits reaction between the stainless steel and the molten aluminum during the subsequent casting operation.

After the coating was dry, 2500 grams of an aluminum-2% copper alloy ingot (cut into two pieces, each 5.1 cm by 2.5 cm by 30.5 cm (1 inch by 2 inch by 12 inch) ) (obtained under the trade designation"1980-A"from Belmont Metal, New York, NY) were then placed in the stainless steel can on top of the assembly. A type-K thermocouple (obtained from Omega Engineering Inc. , Stamford, CT) was placed at the top of the die assembly to monitor the temperature of the aluminum-2% copper melt during the casting process. A hold-down rod was also affixed to the top of the graphite assembly to prevent that assembly from floating in the molten aluminum during the casting. The stainless steel can was then placed inside the pressure vessel of the pressure casting machine (obtained from Process Engineering Technologies, Plaistow, NH), and the pressure vessel closed. The

size of the pressure casting vessel was about 16.9 cm (inner diameter) by 88. 9 cm (in length).

The closed casting vessel was then evacuated of air with a vacuum pump until a pressure of less than one torr was achieved. The power to the electrical furnace of the pressure caster was then turned on, and the graphite die assembly and Al-2% Cu alloy ingot were heated to a temperature of 710°C (about 100°C above the melting point of the alloy).

The average heating rate was about 340°C per hour. After a melt temperature of 710°C was reached, the furnace power was turned off, and the vacuum valve to the vessel closed, thereby isolating the vessel from the vacuum pump.

A low pressure valve connected to pressurized, bottled argon tanks was then opened to back-fill the vessel with argon to an initial low pressure of 1.79 MPa (260 psi).

When this pressure was reached, the low-pressure valve was closed and a high-pressure argon valve was opened until a pressure of 8.96 MPa (1300 psi) was reached. The pressure was maintained at 8.96 MPa 1% (1300 psi 15 psi) for 15-20 minutes forcing the molten aluminum-2% copper alloy to infiltrate the preforms completely.

Next, the pressure was allowed to decay with the temperature to 500°C. When the temperature fell below 500°C, the vessel exhaust valve was opened, and the argon was vented to the atmosphere. The vessel was then opened, and the stainless steel can was removed. The die assembly was separated from the can, and the four cast aluminum matrix composite plates were removed from the graphite mold.

The cast plates were surface ground with a vertical spindle diamond grinder (#11 Blanchard grinder obtained from Precision Instruments, Minneapolis, MN) to a thickness of 0.25 cm (0.1 inch). The plates were then sliced lengthwise to a width of 0.94 cm (0.37 inch) to make 15.2 cm (6 inch) by 0.95 cm (0.375 inch) by 0.25 cm (0.1 inch) plates.

Two plates were then surface treated/coated as follows. Both plates were abraded with a 100 grit grinder wheel (obtained under the trade designation"DIAMOND WHEEL, ASD100"from Norton Company, Worcester, MA), and cleaned with a standard lacquer thinner (available as Grade 401 from HCI, St. Paul, MN) by rubbing with paper towels until no visible residue could be removed from the surface.

The two resulting plates were coated (by Co-Operative Plating Co. , St. Paul, MN), via electroless deposition, with about 3 micrometers of nickel, followed by electroplating about 12 micrometers of silver.

An optical photomicrograph at 550x of a polished cross-section of an Example 1 insert is shown in FIG. 12. Insert 120 includes aluminum-2% copper matrix 124, alumina ("NEXTEL 610" ; about 11 micrometers in diameter) fiber 122, nickel coating 128 and silver coating 126.

Each plated insert was preheated in air for 15 minutes to a temperature of about 750°C. The heated insert was then placed in a steel die cavity. Referring to FIG. 13, die 130 included base 132 (9.8 cm by 9.8 cm by 14 cm (3.9 in. by 3.9 in. by 5.5 in. ) ) with rectangular slot 134 (1.3 cm by 0.25 cm (0.5 in. by 0.1 in. ) ) for the insert, and upper part 136 (7.3 cm by 7.3 cm by 12.7 cm (29 in by 2.9 in by 5.0 in) ). Upper part 136 includes cavity 138 which had diameter 2.54 cm (1 inch) and 10.2 cm (4 inch) deep. Upper part 136 was coated with a boron nitride release agent (obtained under the trade designation "COMBAT BORON NITRIDE AEROSOL SPRAY CC-18"from The Carborundum Corp. , Amherst, NY) and preheated to about 300°C. Within 4 seconds, a molten aluminum alloy (obtained under the trade designation"A356"from Alcan Inc., Montreal, Quebec) at a temperature of about 735°C was then poured into the steel die cavity around the insert and allowed to solidify. When the temperature cooled to about 500°C, the insert and casting assembly were removed from the die cavity.

The two resulting aluminum matrix composites, Examples la and Ib, were sectioned into 1.16 cm (0.46 inch) by 2.5 cm (1 inch) diameter test samples. The sections were cut perpendicular to the longitudinal axis of the insert.

A compressive shear test was conducted to evaluate the"Bond Strength"between the insert and the aluminum cast around the insert. A schematic of the compressive shear test equipment is shown in FIG. 14, wherein compressive shear test equipment 140 included pushout tool 141, test sample 142, support block 143, and 100,000 Newton (22,482 pounds) compressive load cell 147.

Pushout tool 141 had a cross-section of 2.36 mm by 9.37 mm (0.0930 inch by 0.3690 inch) at the point of contact with insert 144 with test sample 142. Pushout tool 141 was clamped in upper jaws 145 of the hydraulic chuck with a hydraulic pressure of 10.34

MPa (1500 pounds per square inch). Support block 143 had a 2.54 cm (1.0 inch) diameter by 0.15 cm (0.06 inch) deep counterbore. A 1.1 cm (0.435 inch) diameter through hole was placed on top of the open jaws 145 of the bottom of hydraulic chuck 146.

Sample to be tested 142 was placed on top of support block 143 and nested in the counterbore for centering of the insert over the through hole. Bottom 148 of hydraulic chuck support 146 was raised until the gap between the upper pushout tool 141, and the insert to be pushed out (i. e. , sample to be tested 144), was 0.025 cm. (0.01 inch). The exposed insert in the test specimen was then visually positioned with the matching tip of pushout tool 141 by manually sliding support block 143 horizontally and rotationally until the cross-sections of the two elements matched.

The test was then conducted by moving the lower hydraulic support chuck up toward fixed pushout tool 141 at a rate of 0.05 cm (0.020 inch) per minute while simultaneously monitoring the load and deflection. The insert was thereby brought into contact with the fixed pushout tool face and the contact force between the two recorded as a function of displacement. The test was discontinued shortly after the peak force was reached and a total deflection of about 0.05 cm (0.020 inch) was obtained.

After completion of the test, the specimen was examined under an optical microscope at 100X magnification to verify that the test insert and pushout tip were properly aligned such that their cross-sections were overlapping, which they were.

The average shear stress was calculated using the following formula: Average Shear Stress = Load at first slippage. N (lbs.) Area of contact between insert and aluminum alloy, m2 (in2).

The loads were plotted as a function of the insert displacement. The load at which the pushout curve had a discontinuity is reported in the Table, below, as 13046 N (2933 pounds) for Example la and 6112 N (1374 pounds) for Example lb, and is the load where there was initial slippage at the interface between the insert and the aluminum cast around the insert.

Table Load at first Average shear Peak bond Example slippage N, (Ibs.) stress, MPa strength, MPa la 13046 (2933) 46.3 138.9 1b 6112 (1374) 21. 7 65. 1 2a 13976 (3142) 49.6 148.8 2b 12708 (2857) 45. 1 135. 3 3a 15270 (3433) 54.2 162.6 3b 15808 (3554) 56. 1 168. 3 4a 17610 (3959) 62.4 187.2 4b 12134 (2728) 43.0 129.0 5a 2442 (549) 8. 6 25.8 5b 2615 (588) 9. 3 27. 9 6a 3469 (780) 12.3 36.9 6b 4141 (931) 14. 7 44. 1 7a 3865 (869) 13.7 41.1 7b 5258 (1182) 18. 6 55. 8 8a 3002 (675) 10.7 32.1 8b 3532 (794) 12. 5 37. 5 9a 2068 (465) 7.3 21.9 9b 3256 (732) 11.5 34.5 10a 5182 (1165) 18.4 55.2 10b 3256 (732) 11. 5 34. 5 lla 2927 (658) 10.3 30.9 11b 3367 (757) 11. 9 35. 7 12a 15065 (3387) 53.4 160.2 12b 10173 (2287) 36. 1 108. 3 Comparative A1 2411 (542) 8.6 25. 8 Comparative A2 1948 (438) 6. 9 20. 7 Comparative B 1 2295 (516) 8.1 24.3 Comparative B2 1535 (345) 5.4 16.2 Comparative B3 2113 (475) 7. 5 22. 5 Comparative C1 2740 (616) 9.7 29.1 Comparative C2 970 (218) 3. 4 10. 2 Comparative D 1 2113 (475) 7.5 22.5 Comparative D2 1130 (254) 4. 0 12. 0 Comparative E 1245 (280) 4. 4 13. 2 Comparative F1 2126 (478) 7.5 22.5 Comparative F2 1535 (345) 5.4 16.2 Comparative F3 1281 (288) 4. 5 13. 5 Comparative G1 2480 (535) 8.5 25.5 Comparative G2 1539 (346) 5. 5 16. 5 Comparative Hl 2126 (478) 7.5 22.5 Comparative H2 3176 (714) 11. 3 33. 9 Comparative I 2798 (629) 9.9 29. 7 Load at first Average shear Peak bond Example slippage, N, (lbs.) stress, MPa strength, MPa Comparative J1 3171 (713) 11.2 33.6 Comparative J2 2104 (473) 7. 5 22. 5 Comparative K 1859 (418) 6. 6 19. 8 Comparative L1 2531 (569) 9.0 27.0 Comparative L2 1806 (406) 6.4 19.2 Comparative L3 1779 (400) 6. 3 18. 9 Comparative M1 3140 (706) 11. 1 33.3 Comparative M2 2971 (668) 10. 5 31. 5 Comparative N1 13638 (3066) 48.4 145.2 Comparative N2 7633 (1716) 27. 1 81. 3 Comparative 0 2139 (481) 7. 6 22. 8

The"Peak Bond Strengths"are also reported in the Table, above. The Peak Bond Strength was calculated using Finite Element Analysis (FEA). Finite Element Analysis (FEA) software (obtained under the trade designation"ANSYS"from Ansys Inc., Canonsburg, PA) was used to model the insert and show that the ratio of peak bond strength to measured average shear stress was approximately 3.0.

The FEA calculation was done as follows. A finite element model of the test specimen geometry was created. The insert was meshed with elements of dimension 0.02 cm by 0.02 cm by 0.05 cm (0.01 inch by 0.01 inch by 0.02 inch) cubes, except at the top of the insert where the mesh size was 0.02 cm in all dimensions. The aluminum was meshed with cubes having sides of 0.05 cm (0.02 inch) near the insert and 0.10 cm (0.04 inch) elsewhere in the modeled test specimen. The FEA software computed the shear stress at points along the surface of the insert for an applied pressure of 533.3 MPa (corresponding to a pushout test load of 2900 pounds). The calculation determined that the peak shear stress across all points of the surface of the insert was 140 MPa, and that the average across the insert surface was 45.8 MPa. The ratio of Peak Bond Strength to average shear stress is thus about 3 to 1.

Load at initial slippage and the corresponding average shear stress and the peak bond strength values are also reported in the Table, above (wherein average values are an averages for the stated number of samples for each Example).

Example 2 Two Example 2 (i. e. , Examples 2a and 2b) aluminum matrix composites were prepared and tested as described for Example 1, except a 400 grit grinder wheel (obtained under the trade designation"DIAMOND WHEEL, ASD400"from Norton Company") was used to abrade the inserts before coating, and the inserts and die were preheated to 550°C and 250°C, respectively.

The load at first slippage, average shear stress, and peak bond strengths for Examples 2a and 2b are reported in the Table, above.

Example 3 Two Example 3 (i. e., Examples 3a and 3b) aluminum matrix composites were prepared and tested as described for Example 1, except before coating the samples were abraded by sandblasting with 50-micrometer diameter glass beads (obtained from Abrasive Systems, Inc., Maple Grove, MN), the plated inserts and die were preheated to 550°C and 250°C, respectively, and the molten aluminum alloy was heated to 760°C.

A plot of the Example 3 compressive shear strengths as a function of the insert displacement under load is shown in FIG. 15. The load at which the pushout curve had a discontinuity is shown by reference number 151. This discontinuity is where there was initial slippage at the interface between the insert and the aluminum cast around the insert.

The load at first slippage, average shear stress, and peak bond strengths for Examples 3 a and 3b are reported in the Table, above.

One Example 3 sample was polished with semi-automatic metallographic grinding/polishing equipment (obtained under the trade name"ABRAMIN"from Struers, 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 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 tlm"from Struers).

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 Struers) and sprayed for 1 second with 3 micrometer diamond grit (obtained under the trade designation"DP-SPRAY, P-3 lem''from Struers). 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 Struers), wetted first with water and colloidal silica suspension (obtained under the trade designation"OP-S SUSPENSION"from Struers) 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.

Examination of the polished cross-section of Example 3 (see FIG. 16) showed no abrupt boundary at interface 162 between insert matrix 166 and casting alloy 163, no discrete layer high in nickel or silver, and a limited degree of mixing of the two aluminum alloys (i. e. , the aluminum alloy of insert 166 and aluminum alloy 163 of the aluminum matrix composite comprising the insert) to a depth of a few fiber diameters.

Example 4 Two Example 4 (i. e. , Examples 4a and 4b) aluminum matrix composites were prepared and tested as described for Example 1, except the die was preheated to 250°C, the insert was preheated to 550° C, and the molten aluminum alloy was heated to 760°C.

The load at first slippage, average shear stress, and peak bond strengths for Examples 4a and 4b are reported in the Table, above.

Example 5 Two Example 5 (i. e. , Examples 5a and 5b) aluminum matrix composites were prepared and tested as described for Example 1, except a 400 grit grinder wheel ("DIAMOND WHEEL, ASD400") was used to abrade the inserts before coating, the die was preheated to 250°C, and the molten aluminum alloy was heated to 760°C.

The load at first slippage, average shear stress, and peak bond strengths for the two samples of Example 5 are reported in the Table, above.

Example 6 Two Example 6 (i. e., Examples 6a and 6b) aluminum matrix composites were prepared and tested as described for Example 1, except the inserts were abraded by sandblasting before coating as in Example 3, the die was preheated to 250°C, and the molten aluminum alloy was heated to 760°C.

The load at first slippage, average shear stress, and peak bond strengths for Examples 6a and 6b are reported in the Table, above.

Example 7 Two Example 7 (i. e., Examples 7a and 7b) aluminum matrix composites were prepared and tested as described for Example 1, except the die was preheated to 250°C, and the molten aluminum alloy was heated to 760°C.

A plot of the Example 7 compressive shear strengths as a function of the insert displacement under load is shown in FIG. 15 for one of the two samples tested. The load at which the pushout curve had a discontinuity is shown by reference number 153, which is the average for the two samples. This discontinuity is where there was initial slippage at the interface between the insert and the aluminum cast around the insert. The load at first slippage, average shear stress, and peak bond strengths for Examples 7a and 7b are reported in the Table, above.

Example 8 Two Example 8 (i. e., Examples 8a and 8b) aluminum matrix composites were prepared and tested as described for Example 1, except the inserts were abraded by sandblasting before coating as in Example 3, the die was preheated to 550°C, and the molten aluminum alloy was heated to 760°C.

The load at first slippage, average shear stress, and peak bond strengths for Examples 8a and 8b are reported in the Table, above.

Example 9 Two Example 9 (i. e., Examples 9a and 9b) aluminum matrix composites were prepared and tested as described for Example 1, except a 400 grit grinding wheel ("DIAMOND WHEEL, ASD400") was used to abrade the inserts before coating, the die was preheated to 500°C, and the molten aluminum alloy was heated to 760°C.

The load at first slippage, average shear stress, and peak bond strengths for Examples 9a and 9b are reported in the Table, above.

Example 10 Two Example 10 (i. e., Examples 10a and lOb) aluminum matrix composites were prepared and tested as described for Example 1, except the die was preheated to 500°C, and the molten aluminum alloy was heated to 760°C.

Example 10 aluminum matrix composite was sectioned into 1.16 cm (0.46 inch) by 2.5 cm (1 inch) diameter test samples. A cross-section of one of the pieces is shown in FIG. 18, wherein aluminum matrix composite article 180 included aluminum 181, and insert 182, which in turn included aluminum-2% copper alloy and alpha alumina ("NEXTEL 610") fibers.

The load at first slippage, average shear stress, and peak bond strengths for Examples 10a and 10b are reported in the Table, above.

Example 11 Two Example 11 (i. e., Examples 1 la and 1 lb) aluminum matrix composites were prepared and tested as described for Example 1, except before coating, grooves parallel to length of the inserts were cut into the surface by diamond grinding, the die was preheated to 500°C, and the molten aluminum was heated to 760°C. The grooves were approximately 0.17 mm deep by 0.3 mm wide with a pitch of 0.62 mm.

The load at first slippage, average shear stress, and peak bond strengths for Examples 11 la and 1 lb are reported in the Table, above.

Example 12 Two Example 12 (i. e. , Examples 12a and 12b) aluminum matrix composites were prepared and tested as described for Example 1, except before coating, grooves perpendicular to the length of the inserts were cut into the surface by diamond grinding, the die was preheated to 500°C, and the molten aluminum alloy was heated to 760°C. The grooves were approximately 0.17 mm deep by 0.3 mm wide with a pitch of 0.62 mm The load at first slippage, average shear stress, and peak bond strengths for Examples 12a and 12b are reported in the Table, above.

Comparative A Two Comparative Example A (i. e., Comparative Examples Al and A2) aluminum matrix composites were prepared and tested as described for Example 1, except the inserts were not coated, and the die was preheated to 500°C.

The load at first slippage, average shear stress, and peak bond strengths for Comparative Examples Al and A2 are reported in the Table, above.

Comparative B Three Comparative Example B (i. e., Comparative Examples B 1, B2, and B3) aluminum matrix composites were prepared and tested as described for Example 1, except the inserts were not coated, and the die was preheated to 400°C.

The load at first slippage, average shear stress, and peak bond strengths for Comparative Examples B 1, B2, and B3 are reported in the Table, above.

Comparative C Two Comparative Example C (i. e., Comparative Examples Cl and C2) aluminum matrix composites were prepared and tested as described for Example 1, except the inserts were not coated, the insert surfaces were abraded with a 400 grit grinding wheel ("DIAMOND WHEEL, ASD400"), the inserts were preheated to 193°C.

The average load at first slippage, average shear stress, and peak bond strengths for Comparative Examples Cl and C2 are reported in the Table, above.

Comparative D Two Comparative Example D (i. e. , Comparative Examples Dl and D2) aluminum matrix composites were prepared and tested as described for Example 1, except the inserts were not coated, and the inserts were preheated to 193°C.

The load at first slippage, average shear stress, and peak bond strengths for Comparative Examples Dl and D2 are reported in the Table, above.

Comparative E A Comparative Example E aluminum matrix composite was prepared and tested as described for Example 1, except the insert was uncoated.

The load at first slippage, average shear stress, and peak bond strength for Comparative Example E are reported in the Table, above.

Comparative F Three Comparative Example F (i. e. , Comparative Examples F1, F2, and F3) aluminum matrix composites were prepared and tested as described for Example 1, except the inserts were uncoated, and a 400 grit grinding wheel ("DIAMOND WHEEL, ASD400") was used to abrade the inserts.

The load at first slippage, average shear stress, and peak bond strengths for the three samples of Comparative Examples F1, F2, and F3 are reported in the Table, above.

Comparative G Three Comparative Example G (i. e. , Comparative Examples G1, G2, and G3) aluminum matrix composites were prepared and tested as described for Example 1, except the inserts were uncoated, and the surfaces of the inserts were sandblasted as in Example 3.

The load at first slippage, average shear stress, and peak bond strengths for Comparative Examples G1, G2, and G3 are reported in the Table, above.

Comparative H Two Comparative Example H (i. e. , Comparative Examples H1 and H2) aluminum matrix composites were prepared and tested as described for Example 1, except the inserts were uncoated, the surfaces of the inserts were sandblasted as in Example 3, and the die was preheated to 400°C.

One Comparative Example H sample was polished as described in Example 3, above. Examination of the polished cross-section of Comparative Example H (see FIG.

17) showed an abrupt boundary, believed to be an oxide layer, at interface 182 between insert matrix 186 and casting alloy 183.

The load at first slippage, average shear stress, and peak bond strengths for Comparative Examples H1 and H2 are reported in the Table, above.

Comparative I A Comparative Example I aluminum matrix composite was prepared and tested as described for Example 1, except the insert was coated with about 12 micrometers of nickel, and the insert was not preheated.

The load at first slippage, average shear stress, and peak bond strength for Comparative Example I are reported in the Table, above.

Comparative J Two Comparative Example J (i. e., Comparative Examples J1 and J2) aluminum matrix composites were prepared and tested as described for Example 1, except the inserts were coated with nickel as in Comparative I, and the die was preheated to 400°C.

The load at first slippage, average shear stress, and peak bond strengths for the two samples of Comparative Example J are reported in the Table, above.

Comparative K A Comparative Example K aluminum matrix composite was prepared and tested as described for Example 1, except the insert was coated with about 12 micrometers of copper, and the insert was not preheated.

The load at first slippage, average shear stress, and peak bond strength for Comparative Example K are reported in the Table, above.

Comparative L Three Comparative Example L (i. e. , Comparative Examples LI, L2, and L3) aluminum matrix composites were prepared and tested as described for Example 1, except the inserts were coated with copper as in Comparative K, and the die was preheated to 400°C.

The load at first slippage, average shear stress, and peak bond strengths for the three samples of Comparative Example L are reported in the Table, above.

Comparative M Two Comparative Example M (i. e. , Comparative Examples M1 and M2) aluminum matrix composites were prepared and tested as described for Example 1, except the inserts had grooves cut into them as in Example 12, the inserts were not coated, the die was preheated to 500°C, and the temperature of the molten aluminum alloy was 760°C.

The load at first slippage, average shear stress, and peak bond strengths for Comparative Examples M1 and M2 are reported in the Table, above.

Comparative N Two Comparative Example N (i. e., Comparative Examples N1 and N2) aluminum matrix composites were prepared and tested as described for Example 1, except the inserts had grooves cut into them as in Example 13, but the inserts were not coated, the die was preheated to 500°C, and the temperature of the molten aluminum alloy was 760°C.

The load at first slippage, average shear stress, and peak bond strengths for Comparative Examples N1 and N2 are reported in the Table, above.

Comparative O A Comparative Example O aluminum matrix composite was prepared and tested as described for Example 1, except the insert was coated with about 12 micrometers of zinc, the die was preheated to 500°C, and the insert was preheated to 291°C.

The load at first slippage, average shear stress, and peak bond strength for Comparative Example O are reported in the Table, above.

Various 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.