Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
1998-08-12
2001-10-02
Derrington, James (Department: 1731)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S097000, C164S103000
Reexamination Certificate
active
06296045
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to ceramic-metal composites.
BACKGROUND OF THE INVENTION
Recently ceramics have been used to make computer components such as disks and E-blocks for hard drives. Ceramics are starting to be used instead of metals (e.g., aluminum) for these components because of their low density and high stiffness. However, ceramics generally have a low toughness (i.e., break easier than metals) and are difficult and costly to form into the final component shape.
More recently an infiltrated aluminum-boron carbide (ABC) composite has been utilized for the above computer components (U.S. Pat. No. 5,672,435). These composites overcome some of the problems of ceramics such as difficulty in forming the part. However these composites require a substantial amount of costly fine boron carbide powder. Also, in making high stiffness ABC composites, almost all of the aluminum must be reacted to form aluminum boride, aluminum borocarbide or aluminum carbide ceramic phases. Consequently, the high stiffness ABC generally has a low toughness and consequently breaks similarly to a ceramic.
Accordingly, it would be desirable to provide a material that overcomes one or more of the problems of the prior art such as one of those described above. It would also be desirable to provide a method of preparing the material.
SUMMARY OF THE INVENTION
A first aspect of the invention is a ceramic-metal composite comprised of an inert ceramic embedded and dispersed in a matrix comprised of a metal, a reactive ceramic and at least one reactive ceramic-metal reaction product wherein grains of the inert ceramic have an average grain size greater than or equal to the average grain size of grains of the reactive ceramic.
A second aspect of the present invention is a method for preparing a ceramic-metal composite, the method comprising,
a) forming a mixture comprised of an inert ceramic powder and a reactive ceramic powder, the inert ceramic powder having an average particle size equal to or greater than the average particle size of the reactive ceramic powder,
b) forming the mixture of step (a) into a porous body and
c) consolidating the porous body in the presence of a metal to form the ceramic-metal composite wherein the composite has at least one reactive ceramic-metal reaction product.
Surprisingly, the method according to the invention produces a ceramic-metal composite that may be as stiff or stiffer than a ceramic-metal body produced using about the same amount of metal and only the reactive ceramic powder. Or, in other words, as stiff or stiffer than a ceramic-metal composite devoid of the inert ceramic. This is surprising since metals generally are much less stiff—that is to say they have a much lower elastic moduli—than ceramics. And, the amount of residual metal would be higher in a composite formed from a porous body having less reactive ceramic powder (i.e., a body containing inert ceramic powder). This surprising stiffness generally coincides with the inert ceramic powder having an average particle size equal to or greater than the reactive ceramic powder. This surprising effect occurs even when the inert ceramic powder, for example, makes up greater than about 40% by volume of the porous body.
The ceramic-metal composite may be used in applications benefiting from properties such as low density and high stiffness. Examples of components include hard drive components (e.g., E-blocks, suspension arms, disks, bearings, actuators, clamps, spindles, base plates and housing covers); brake components (e.g., brake pads, drums, rotors, housings and pistons); aerospace components (e.g., satellite mirrors, housings, control rods, propellers and fan blades); piston engine components (e.g., valves, exhaust and intake manifolds, cam followers, valve springs, fuel injection nozzles, pistons, cam shafts and cylinder liners) and other structural or recreational components (e.g., bicycle frames, robot arms, deep sea buoys, baseball bats, golf clubs, tennis rackets and arrows).
DETAILED DESCRIPTION OF THE INVENTION
The Ceramic-Metal Composite
The ceramic-metal composite is comprised of an inert ceramic embedded and dispersed in a matrix. The matrix is comprised of a metal, a reactive ceramic and at least one reactive ceramic-metal reaction product. The reactive ceramic-metal reaction product is a reaction product of the reactive ceramic and the metal. The metal may be any metal capable of reacting with the reactive ceramic to form the reaction product. Preferred metals include silicon, magnesium, aluminum, titanium, vanadium, chromium, iron, copper, nickel, cobalt, tantalum, tungsten, molybdenum, zirconium, niobium, alloys of the previously mentioned metals and mixtures thereof. More preferred metals include aluminum, silicon, titanium, magnesium, alloys and mixtures thereof. Most preferably the metal is aluminum and alloys of aluminum, such as those that contain one or more of Cu, Mg, Si, Mn, Cr and Zn. Exemplary aluminum alloys include Al—Cu, Al—Mg, Al—Si, Al—Mn—Mg and Al—Cu—Mg—Cr—Zn. Specific examples of aluminum alloys include 6061 alloy, 7075 alloy and 1350 alloy, each available from the Aluminum Company of America, Pittsburgh, Pa.
The amount of metal in the matrix may be any useful amount, but generally is at most about 50% by volume of the matrix. Preferably the amount of metal is at most about 40%, more preferably at most about 25%, even more preferably at most about 20% and most preferably at most about 15% to preferably at least about 1%, more preferably at least about 2% and most preferably at least about 3% by volume of the matrix.
The reactive ceramic may be any ceramic capable of reacting with the metal to form the reactive ceramic-metal reaction product in the ceramic-metal composite. The reactive ceramic may be, depending on the metal, a boride, oxide, carbide, nitride, silicide or combinations or mixtures of these. Combinations include, for example, borocarbides, oxynitrides, oxycarbides and carbonitrides. Boron containing ceramics such as a boride, borocarbide and boron carbide are generally preferred. Examples of specific preferred reactive ceramics include B
4
C, TiB
2
, SiB
6
, SiB
4
, ZrC, ZrB or mixtures thereof. The most preferred reactive ceramic is boron carbide.
The reactive ceramic-metal reaction product may be any ceramic that is a reaction product of the metal and the reactive ceramic. For example, a preferred ceramic-metal composite is a boron carbide-aluminum composite containing; an inert ceramic (i.e., Al
2
O
3
), a reactive ceramic (i.e., B
4
C) and a reactive ceramic-metal reaction product such as AlB
2
, Al
4
BC, Al
3
B
48
C
2
, AlB
12
, Al
4
C
3
and AlB
24
C
4
.
The inert ceramic is a ceramic that essentially fails to react with the metal, which generally coincides with less than about 5% by volume of the inert ceramic reacting with the metal to form a reaction product under the conditions used to form the composite. Preferably, less than 3%, more preferable less than 1% and most preferably essentially 0% by volume of the inert ceramic reacts with the metal. The inert ceramic essentially failing to react with the metal, generally, coincides with the ceramic-metal composite containing less than about 2% by volume of a metal-inert ceramic reaction product. The amount of metal-inert ceramic reaction product may be determined by a known technique such as X-ray diffraction. Preferably, the ceramic-metal composite contains at most about 0.5% by volume, more preferably at most about 0.1% by volume and most preferably essentially no metal-inert ceramic reaction product.
Ceramics that may be suitable as inert ceramics include, for example, borides, oxides, carbides, nitrides, suicides or combinations thereof. Examples of combinations include borocarbides, oxynitrides, oxycarbides and carbonitrides. Preferably, the inert ceramic is silicon carbide, aluminum nitride, aluminum oxide or mixtures thereof.
The inert ceramic is embedded and dispersed in the matrix and has an average grain size equal to or greater than the average grain size of the reactive cerami
Fox Richard T.
Han Chan
Pyzik Aleksander J.
Derrington James
Nilsen Kevin J.
The Dow Chemical Company
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