US20040118547A1

US20040118547A1 - Machineable metal-matrix composite and method for making the same

Info

Publication number: US20040118547A1
Application number: US10/326,151
Authority: US
Inventors: Alexander Brown; Eric Klier; Frank Nolfi
Original assignee: Chesapeake Composites Corp
Current assignee: DSC MATERIALS Inc
Priority date: 2002-12-23
Filing date: 2002-12-23
Publication date: 2004-06-24
Also published as: AU2003296914A8; WO2004061139A2; AU2003296914A1; WO2004061139A3

Abstract

A method for producing a metal matrix composite having improved properties includes the step of forming a sintered ceramic preform including a network of uniformly distributed ceramic particles having a particle size of 1 micron or less and being bonded together at their points of contact by sintering. After sintering to form a preform, the preform is placed in a mold and infiltrated with molten metal. The molten metal is then solidified to form a shaped body. This shaped body is then subjected to sufficient strain to eliminate at least 50% and preferably 80% of the bonds in the network. The shaped body is then subjected to a metal forming step such as wrought or semisolid forming.

Description

FIELD OF THE INVENTION

The present invention relates to metal-matrix composites and methods for their manufacture and more particularly to metal-matrix composites including uniformly distributed ceramic particles wherein at least about 50 percent of the particles are free of bonding to one another.

BACKGROUND FOR THE INVENTION

Metal-matrix composites and methods for producing those composites are disclosed in U.S. Pat. Nos. 5,511,603 and 5,702,542 which are incorporated herein in their entirety by reference. As disclosed therein the manufacturing methods include providing a ceramic preform having a uniform distribution of ceramic particles sintered to one another at the points of contact. The particles have an average particle size of no greater than 1.0 μ, and at least one-half of the volume of the preform is occupied by porosity. The preform is then placed into a mold and contacted by molten metal. The molten metal is forced into the pores of the preform and permitted to solidify to form a solid metal-matrix composite. This composite is machineable with a high-speed steel (HSS) bit for greater than about one minute without excessive wear occurring to the bit. Metal-matrix composites may include Al., Li., Be., Pb., Au., Sn., Mg., Ti., Cu., and Zn. Preferred ceramics include oxides, borides, nitrides, carbides, carbon or a mixture thereof. Inert gas pressures of less than about 3,000 psi can be used to infiltrate the preform.

The metal-matrix composites disclosed in the aforementioned patents combine the high-strength stiffness and wear resistance of ceramics with the machineability, toughness and formability of metals. A small characteristic reinforcement size of less than about 1 μ in conjunction with a large volume of porosity and a substantially uniform distribution of ceramic particles in a sintered preform are employed to provide improved temperature strengths increased modulus and excellent machineability and ductility even at high ceramic loadings. Such compacts have been machined using only high-speed steel milling, drilling and tapping tooling without experiencing difficulty. Excellent surface finishes were produced.

The metal-matrix composites exhibit high-strength at room and elevated temperatures since the small reinforcement size and interparticle spacing meets the criteria for dispersion strengthening. The small uniformly distributed ceramic particles permit the composite to behave more like a metal than a typical metal-matrix composite permitting their use in applications requiring greater ductility, toughness and formability. The particular metal infusion procedures are adaptable to multiple alloy and ceramic pairings and permit greater latitude for increasing the tensile modulus as loadings approach 50 volume percent. Specific reinforcement ceramics and volume fractions can be selected which will permit designable engineered properties dictated by the application including high elastic modulus, strength and ductility.

Notwithstanding the advantages of metal-matrix composites, of the aforementioned metal-matrix composites, it has been found that a significant improvement can be made in metal forming with a product and process in accordance with the present invention.

SUMMARY OF THE INVENTION

In essence the present invention contemplates a method for producing a metal-matrix composite comprising a uniform distribution of sintered ceramic particles having a particle size of no greater than about one micron and a metal or alloy substantially uniformly distributed with the ceramic particles. Those particles comprise at least 15 volume percent of the metal matrix which is capable of being machineable with a high-speed steel (HSS) bit for greater than about one minute without excessive wear to the bit. In a metal-matrix composite in accordance with the present invention at least 50 percent and preferably about 80% of the particles are free of bonding to another particle.

The invention also contemplates a method for forming a metal-matrix composite comprising the steps of forming a sintered ceramic preform including a network of uniformly distributed ceramic particles having a particle size of one micron or less and being bonded together at their points of contact by sintering to provide a preform. After forming a preform, the preform is placed in a mold and infiltrated with molten metal. The molten metal is then solidified to form a shaped body. This shaped body is then subjected to sufficient strain to eliminate at least 50 percent of the bonds in the network. For example, the shaped body may be subjected to strain by upsetting, extrusion, twisting or possibly by heating and cooling or by passing a sheer wave such as an acoustic wave through the body. The shaped body is then subjected to a metal forming step such as forging or semisolid forming.

In one preferred embodiment of the invention, a metal matrix composite is produced by forming a sintered ceramic preform which includes a network of uniformly distributed particles having a particle size of between about 0.01 and 0.5 μ. These particles are then bonded together by sintering to thereby form a ceramic preform. The ceramic preform is then placed in a mold and infiltrated with molten aluminum. The infiltrated aluminum is then solidified to form a shaped body or billet. This billet is sliced into discs and the discs heated to a temperature of between about 450° C. and about 600° C. and subsequently subjected to sufficient strain to eliminate at least about 50% of the sintered bonds as for example by compressing the discs by between about 2% to 10% along its axis to form a first product. The compressed discs or first product is then semisolid or wrought formed into a piston shape or other preselected shape which is net formed and ready for final machining.

DETAILED DESCRIPTION OF THE INVENTION

Machineable metal-matrix composites (MMCs) are derived from combining ceramic particles of no greater than about one micron with molten metal in an extremely uniform manner. By employing smaller ceramic particles of submicron size and distributing them throughout the metal matrix so as to avoid agglomeration, both high ductility and strength can be provided to the composite without limiting machineability. In one embodiment of the invention at least 80 percent of the ceramic particles are uniformly distributed on a scale of 3 times the particle size and more preferably at least 90 percent of the ceramic particles are uniformly distributed on a scale of twice the particle size. This degree of fine particle distribution virtually eliminates large inclusions and agglomerates which detract from the ductility, strength and machineability of the composite.

The MMCs can be made from many different combinations of matrix material and reinforcing particles to develop whatever special set of properties is required for each application. This invention contemplates employing ultra high-strength metal matrixes including those having yield strengths of about 70 to 2000 MPa. Such metals include for example cobalt and its alloys, martensitic stainless steels, nickel and its alloys and low-alloy hardening steels. High-strength metals and alloys are also potential candidates for the matrixes including tungsten, molybdenum and its alloys, titanium and its alloys, copper casting alloys , bronzes, coppers, niobium and its alloys and super alloys containing nickel, cobalt and iron. Medium strength metals and alloys can also be considered including hafnium, austenitic stainless steels, brasses, aluminum alloys between 2000 and 7000 series, beryllium-rich alloys, depleted uranium, magnesium alloys, silver, zinc, casting alloys, coppers, copper nickels, copper nickel zincs and other materials having yield strengths of about 40 to 690 MPA. Finally the invention optionally employs low-strength, low-density alloys for the matrixes of the invention. Such metals are represented by gold, cast magnesium alloys, platinum, aluminum alloys of the 1,000 series, lead and its alloy and tin and its alloys. These materials have a yield strength of only about 5 to 205 MPA. Most desirably, the invention employs lightweight metals and those which are relatively inexpensive and widely available such as aluminum, lithium, beryllium, lead, tin, magnesium, titanium and zinc and metals which have superior electrical properties such as copper, silver and gold. All of these selections can be provided in commercially pure or alloyed form. Specific alloys which have be recognized to have particular usefulness in MMCs include Al-1Mg-0.6Si., Al-7 Si-1Mg., Al-4.5Cu., Al-7 Ng-2 Si., and Al—Fe—B—Si.

Although alloys and commercially pure metals can be employed to produce the matrixes, a pure metal is generally the matrix of choice since ceramic dispersion strengthening is desired. A pure metal also offers enhanced corrosion resistance as compared to alloys and eliminates the effect of overaging of precipitates. Pure metals also boost elevated temperature capability by increasing the homologous melting point over comparable alloys. Finally, pure metals eliminate the difficulties associated with microsegregation and macrosegregation of the alloying elements in non-eutectic alloys during solidification.

The ceramic or second phase constituents of the metal-matrix composites are desirably of a size which does not interfere with machining by HSS tooling. For example, machineability can be preserved only if the particles are less than about one micron although a range of about 0.01 to 0.5 microns is preferred. The ceramic particles should be thermally and chemically stable for the time and temperature of the particle fabrication process and environmental conditions observed.

These ceramic particles should not be decomposed at high temperatures, nor react with a metal matrix. If they tend to diffuse into the matrix, diffusion of the reinforcement must be slow so that the strength of the composite does not seriously degrade. Ultrafine reinforcement particles having a volume fraction of about 20 to 40 percent are particularly advantageous in yielding composites with improved Young's modulus, ductility and machineability.

Examples of second phase ceramic candidates include borides, carbides, oxides, nitrides, silicates, sulfides and oxysulfides of elements which are reactive to form ceramics including, but not limited to, transition elements of the third to sixth groups of the periodic table. Particularly useful ceramic-forming or intermetallic-compound forming constituents include aluminum, titanium, silicon, boron, molybdenum, tungsten, niobium, vanadium, zirconium, chromium, hafnium, yttrium, cobalt, nickel, iron, manganesium, tantalum, thorium, scandalum, lanthanum and rare earth elements. More exotic ceramic materials include titanium diboride, titanium carbide, zirconium diboride, zirconium disilicide and titanium nitride.

Carbon-based ceramics can also be useful as the ceramic phase including natural and synthetic diamonds, graphite, fullerenes, diamond-like graphite etc. Certain ceramics because of their availability, ease of manufacturing, low cost or exceptional strength in inducing properties are most desirable. These include Al ₂O₃, SiC, B₄C, MgO, Y₂O₃, TiC, graphite, diamond, SiO₂, ThO₂, and TiO₂. These ceramic particles desirably have an aspect ratio of no greater than about 3:1 and preferably no greater than about 2:1 but can be represented by fibers, particles, beads and flakes for example. However, particles are preferred for machineability.

Alternatively, the ceramic reinforcement can have aspect ratios ranging from equiaxed to platelets and spheredized configurations. The particle size distribution can range from mono-sized to a gausean distribution or a distribution having a wide tail at fine sizes. These particles can be mixed using a variety of wet and dry techniques including ball milling and air abrasion.

The preferred binders employed in connection with the ceramic reinforcements can include inorganic colloidal and organic binders such as sintered binders, low temperature and high temperature colloidal binders. Such binders may include polyvinyl alcohol, methal cellulose, colloidal alumina and graphite.

A composite material was prepared having a commercially pure aluminum matrix including 25 volume percent Al ₂O₃, about 0.2 micron average particle size on a population basis. As a preliminary step, the raw materials were weighed out as follows:

Reinforcement: A 16SG, calcined Al ₂O₃, Alcoa Industrial Chemical Division, 259.8 grams.

Carrier: POLAR distilled Water, Polar Water Company, 1205.8 grams.

Filler: Micro 450 (M-450) graphite, Asbury Graphite Mills, Inc., 184,6 grams.

Colloidal Binder: Inorganic NYACOL, AL20, high temperature coating/binder, Nyacol Products, Inc., 86.0 grams.

This mixture was combined in a mill using the following mill parameters: slurry solids content of 10% and mill fill level of 30%. The slurry batch was milled for about 23 to 25 hours, removed from the mill, and disposed in a pressure filtration unit. The slurry was filtrated at 350 psi for about 36 to 60 hours. When filtration was complete, the green preform was removed from the filtration unit. It was measured to have dimensions of about 4.9 cm in diameter×12 cm long. The green preform had a reinforcement loading of about 22 vol. %. The green preform was then dried at ambient conditions until a weight loss of at least about 25 wt. % had been achieved.

The dry preform was then placed in a furnace and fired according to the following scheduled:



	Ramp	Ramp	Hold	Hold
Ramp	Rate	Time	Temp	Time
Seq.	(° C./hr)	(hr)	(° C.)	(hr)

½	25	14	325	2
¾	50	12	900	30
⅚	50	6	1,200	1.5
⅞	100	12	22	24

The fired preform had a loading of about 25 vol. % of sintered ceramic particles. It was removed and inspected, and a weight loss of about 40 wt. % was noted. This weight loss insured that all filler material had been removed.

A mild steel infiltration crucible was then prepared by coating with a graphite wash coating DAG 154 Graphite Lubricating/Resistance Coating, available from Achesion Colloids Company. The interior of the crucible was then lined with GRAFOIL graphite paper, Grade GTB available from UCAR Carbon Company, Inc. The fired preform was inserted into the lined crucible and a preform support rod was inserted to prevent floating. The crucible was then inserted into the pressure infiltration unit, which was custom built. The pressure infiltration unit was evacuated , and then preheated using the following heat cycle:



	Ramp	Hold	Hold
Ramp	Time	Temp	Time
Seq.	(hr)	(° C.)	(hr)

½	2	200	0.05
¾	8	700	2

Approximately 650 grams of commercially pure aluminum (99.9% aluminum, 2 to 5 shot available from Alcoa) was then melted in an electrical resistance furnace and covered with Flux No. 770 cover Flux, available from Asbury Graphite Inc. The infiltration unit was then back-filled with argon. The crucible was removed from the pressure infiltration unit, and the molten alloy was poured into the crucible which caused the argon to bubble to the top of the crucible. The crucible was then placed into the pressure infiltration unit, and it was again evacuated. After evacuation, the unit was pressurized with argon to about 2,150 psi in about 40 to 80 seconds and held for five minutes. The unit was then vented, and the crucible was placed onto a water-cooled chill at the bottom of the pressure infiltration unit. The unit was once again repressurized to 1,000 psi for solidification. The mixture was permitted to cool for about one hour until directionally solidified. The sample was removed from the pressure infiltration unit, the crucible was cut off, and the alloy head was removed.

Under a scanning electron microscope, a fracture surface of one sample of the above composite was visually inspected at 35,000×. The observed particle size was found to be about 0.05 to 0.4 microns, with 0.2 microns being typical, and an interparticle spacing of about 0.05 to 0.4 microns was measured.

In the practice of the present invention, it is important to break up the sintered network, i.e. the bonds at the points of particle to particle contact before wrought forming or semisolid forming. As used herein, wrought forming means forging, extrusion, hot rolling and related processes. This step is typically done by a so-called upset step wherein a billet of a metal matrix composite such as the one prepared above, is heated to a temperature below the melting temperature of the metal and then deformed with a component of shear deformation. For example, a pure aluminum based metal matrix composite is heated to about 450-6000 C. The matrix billet is then compressed along its longitudinal axis by about two to about 10% . In practice, the matrix is subjected to a strain rate of about 10 ⁻¹to a cost limited strain rate and preferably a strain rate of between about 4.44×10⁻³/sec. to about 6.0×10⁻²sec. For example, at a strain rate of 4.44×10⁻³/sec., a 1 ½ inch diameter billet underwent a 9.29% reduction in height over about 19 seconds. For aluminum, at a strain rate of about 1/sec. or greater significant problems with cracking occurred at a deformation of about 20%.

For manufacturing purposes, it is desirable to complete the so-called upset or other steps in breaking the particle to particle bonds as quickly as possible. However, it is presently believed that the strain rate can be tailored to provide the amount of prior strain needed for subsequent wrought or semisolid forming within an optimum time schedule. It is believed that an optimal strain rate can be applied to provide sufficient deformation without cracking for any particular application. It is also believed that the break-up of the bonds can be accomplished by deformation of a body so that the bonds are broken throughout the body.

It has also been found, that without preliminary strain, a billet as described above will exhibit severe cracks upon deformation of about 10 to 20%. By contrast, the same materials are capable of as much as 80 to 90% deformation without cracking after being subjected to sufficient strain to break-up essentially all of the bonds as for example 50 to 80% or more. Therefore, final products can be produced when the net shape includes displacements of at least 25% without cracking and when portions of the final shape have been displaced by at least 50% and up to 80%-90% all without cracking.

The degree of break-up of the bonds was shown by removing the aluminum metal from the matrix by dissolving the aluminum in sodium hydroxide solution. After removal, the ceramic particles remained and upon examination showed no perceptible bonding. By contrast, removal of the metal from billets which had not been upset or otherwise subjected to strain and which had not been subjected to subsequent forming techniques left a residue of bridged particles and in essence a return to the original preform.

EXAMPLE 1



Material	2024 aluminum with 30 volume percent
	sub-micron alumina.
Weight:	427 grams
Diameter:	1.590 inches
Length:	4.140 inches
Volume:	134.7 cc
Density:	3.170 gram/cc
Upset temperature:	450° C
Upset strain rate:	4.44 × 10⁻³/sec.
Upset total strain:	9.29%
Semi-solid forming temperature:	725° C
Semi-solid ram rate:	80 inches/sec.
Semi-solid die temperature:	between 350 and 600° C
Semi-solid flow stress:	between 270 and 3730 psi
Yield Strength:	441 MPa
Ultimate tensile strength:	538 MPa
Tensile elongation:	2.5%
Young's modulus:	144 GPa
Thermal expansion:	16.5 ppm/° C

For comparison, the handbook of mechanical performance of 2024-T4 aluminum is:



	2024 yield strength:	325 MPa
	2024 ultimate tensile strength:	470 MPa
	2024 tensile elongation:	20.0%
	2024 Young's modulus:	70 GPa
	2024 thermal expansion:	22.5 ppm/° C

EXAMPLE 2



Material:	6061 aluminum with 30 volume percent
	sub-micron alumina.
Weight:	375 grams
Diameter:	1.573 inches
Length:	3.816 inches
Volume:	121.5 cc
Density:	3.09 gram/cc
Upset temperature:	450° C
Upset strain rate:	about 6 × 10⁻²/sec.
Upset total strain:	about 10%
Semi-solid forming temperature:	725° C
Semi-solid ram rate:	80 inches/sec.
Semi-solid die temperature:	between 350 and 600° C
Semi-solid flow stress:	between 270 and 3730 psi
Yield Strength:	255 MPa
Ultimate tensile strength:	400 MPa
Tensile elongation:	5.0%
Young's modulus:	124 GPa
Thermal expansion:	16.5 ppm/° C

For comparison, the handbook of mechanical performance of 6061-T4 aluminum is:



	6061 yield strength:	145 MPa
	6061 ultimate tensile strength:	240 MPa
	6061 tensile elongation:	22.0%
	6061 Young's modulus:	70 GPa
	6061 thermal expansion:	22.3 ppm/° C

EXAMPLE 3



Material:	1090 (pure) aluminum with 30 volume
	percent
sub-micron alumina.
Weight:	354 grams
Diameter:	1.570 inches
Length:	3.700 inches
Volume:	117.4 cc
Density:	3.02 gram/cc
Upset temperature:	600° C
Upset strain rate:	about 6 × 10⁻²/sec.
Upset total strain:	about 10%
Semi-solid forming temperature:	725° C
Semi-solid ram rate:	80 inches/sec.
Semi-solid die temperature:	between 350 and 600° C
Semi-solid flow stress:	between 270 and 3730 psi
Yield Strength:	207 MPa
Ultimate tensile strength:	225 MPa
Tensile elongation:	2.5%
Young's modulus:	83 GPa
Thermal expansion:	16.5 ppm/° C

For comparison, the handbook of mechanical performance of 1090 (pure) aluminum is:



	2024 yield strength:	35 MPa
	2024 ultimate tensile strength:	90 MPa
	2024 tensile elongation:	70.0%
	2024 Young's modulus:	70 GPa
	2024 thermal expansion:	23 ppm/° C

While the invention has been disclosed in connection with its preferred embodiments, it should be recognized and understood that changes and modifications may be made therein without departing from the scope of the appended claims. [0039]

Claims

What is claimed is:

1. A metal-matrix composite comprising a uniform distribution of calcined ceramic particles having an average particle size no greater than about one micron and a metal or alloy substantially uniformly distributed with said ceramic particles comprising at least 15 volume percent of the metal matrix and wherein at least 50 percent of said particles are free of bonds to another particle.

2. A metal-matrix composite comprising a uniform distribution of calcined ceramic particles having an average particle size no greater than about one micron and a metal or alloy substantially uniformly distributed with said ceramic particles in which said ceramic particles comprise at least about 15 volume percent of the metal matrix, wherein at least 80 percent of said ceramic particles are uniformly distributed on a scale of three times the particle size and wherein at least 80 percent of said particles are free of bonds to another particle.

3. The metal-matrix composite according to claim 2 wherein at least 90 percent of said ceramic particles are uniformly distributed on a scale of twice the particle size.

4. The metal-matrix composite according to claim 3 wherein at least 50 percent of said particles are free of bonds to another particle.

5. The metal-matrix composite according to claim 4 in which said metal-matrix composite is machineable with a high-speed steel bit for greater than about one minute without excessive wear to said bit.

6. The metal-matrix composite of claim 5 wherein said ceramic particles have an aspect ratio of no greater than about 3:1.

7. The metal matrix composite of claim 6 wherein said ceramic particles have an aspect ratio of no greater than about 2:1.

8. The metal-matrix composite according to claim 7 in which said ceramic particles are of the material selected from the group consisting of oxides, borides, nitrides, carbides, carbon or a combination thereof; and in which said metal or alloy is selected from the group consisting of Al, Li, Be, Pb, Ag, Sn, Mg, Ti, Cu, Zn or mixtures thereof.

9. The metal-matrix composite of claim 7 wherein a three-inch diameter billet of said composite is capable of a 50 percent deformation along its longitudinal axis without cracking.

10. The metal-matrix composite of claim 9 wherein a three-inch diameter billet is capable of an 80 percent deformation along its longitudinal axis without cracking.

11. The metal-matrix composite of claim 7 in which the metal-matrix composite has been deformed by at least about 80 percent without cracking.

12. A method for forming a metal-matrix composite comprising the steps of:

forming a sintered ceramic preform including a network of uniformly distributed ceramic particles having a particle size of one micron or less and being bonded together at their points of contact by sintering;

placing the ceramic preform in a mold;

infiltrating the preform with molten metal;

solidifying the molten metal to thereby form a shaped body;

subjecting the shaped body to sufficient strain to eliminate at least 50 percent of the sintered bonds in the network; and

subjecting the strained shaped body to a metal forming step.

13. The method for forming a metal-matrix composite according to claim 12 in which the strained shaped body is subjected to wrought forming.

14. The method for forming a metal-matrix composite according to claim 12 in which the metal forming step is semisolid forming.

15. The method for forming a metal-matrix composite according to claim 12 in which at least 80 percent of the bonds in the network are broken.

16. A method for forming metal-matrix composites comprising the steps of:

providing a slurry of ceramic particles in a liquid wherein substantially all of the particles have a particle size of one micron or less;

separating the ceramic particles from the liquid to provide a ceramic preform having a substantially uniform distribution of ceramic particles and sintering the ceramic particles to form a network of particles bonded together at their points of contact;

placing the sintered ceramic preform in a mold;

contacting the ceramic preform with a molten metal;

causing the molten metal to penetrate the preform; and

solidifying the molten metal to thereby form a shaped body; and,

subjecting the shaped body to sufficient strain to break at least 50 percent of the bonds in the network to thereby form a metal-matrix composite.

17. The method for forming metal-matrix composites according to claim 16 in which the slurry is subjected to a milling step.

18. The method for forming metal-matrix composites according to claim 17 in which the step of causing the molten metal to penetrate into the preform is accomplished by pressure infiltration.

19. The method for forming metal-matrix composites according to claim 18 in which the steps of subjecting the shaped body to strain comprises compressing the shaped body from about 0.1 to about 10 percent along a first axis.

20. The method for forming metal-matrix composites according to claim 19 which includes a further step of wrought forming the metal-matrix composite into a different shape.

21. The method for forming metal-matrix composites according to claim 19 which includes a further step of semi-solid forming the metal-matrix composite into a different shape.

22. The method for forming metal-matrix composites according to claim 20 in which the step of subjecting the shaped body to strain is applied at a rate of between about 4.44×10⁻³/sec. and about 6.0×10⁻²/sec.

23. A method for forming a metal-matrix composite comprising the steps of:

forming a sintered ceramic preform including a network of uniformly distributed particles having a particle size of between about 0.01 and 0.5μ and being bonded together at their points of contact by sintering;

placing the ceramic preforms in a mold;

infiltrating the preform with a molten metal;

solidifying the molten metal to thereby form a shaped body;

heating the shaped body to a temperature of less than its melting point at about 300° C. below its melting point; and

subjecting the heated shaped body to sufficient strain to eliminate at least 50% of the sintered bonds in a network.

24. A method for forming a metal-matrix composite according to claim 23, in which the ceramic preform is infiltrated with molten aluminum and the shaped body is heated to a temperature of between about 450° C. to about 600° C.

25. A method for forming a metal-matrix composite comprising the steps of:

a) forming a sintered ceramic preform including a network of uniformly distributed particles having a particle size of between about 0.01 and 0.5 μ and being bonded together at their points of contact by sintering;

b) placing the ceramic preform in a mold;

c) infiltrating the preform with a molten aluminum;

d) solidifying the molten aluminum to form a shaped body;

e) heating the shaped body to a temperature of between about 450° C. to about 600° C.; and

f) compressing the shaped body along a first axis by about two to about ten percent to form a first product.

26. A method for forming a metal-matrix composite according to claim 25, which includes the added step of semisolid forming the preselected shape or first product from the compressed shaped body.

27. A method for forming a metal-matrix composite according to claim 25, which includes the added step of wrought forming the preselected shape or first product from the compressed shaped body.

28. A method for forming a metal-matrix composite according to claim 26, which includes the step of cooling the first product from step f) before semisolid forming a preselected shape.

29. A metal-matrix composite comprising a uniform distribution of calcine ceramic particles having an average particle size of no greater than about 0.5 μ and an aluminum metal substantially uniformly distributed with said ceramic particles comprising at least 15 volume percent of the metal matrix and wherein at least 50% of said particles are free of bonds to another particle and wherein the net shape includes displacement of a portion thereof by at least 25% without cracking.

30. A metal-matrix composite comprising a uniform distribution of calcine ceramic particles having an average particle size of no greater than about 0.5μ and an aluminum metal substantially uniformly distributed with said ceramic particles comprising at least 15 volume percent of the metal matrix and wherein at least 50% of said particles are free of bonds to another particle and wherein the net shape includes wherein portions have been displaced by at least 50%.

31. A method for forming metal-matrix composites according to claim 15 in which the bonds in the network are broken throughout the body before the metal forming step.