DE69534107T2 - MMC AND LIQUID METAL INFILTRATION PROCESS - Google Patents

Description

AREA OF INVENTION

These The invention relates to the production of metal-ceramic composite materials with a high tensile modulus, good ductility, toughness, formability and machinability Machinability and special metal-matrix composites with lightweight Weight, the uniform include distributed ceramic particles, which are the mechanical Increase the properties of the composite, without its ductility and machinability to reduce.

BACKGROUND THE INVENTION

Metal Matrix Composites (MMCs [metal matrix composites]) are metals or alloys that with tiny inclusions reinforced by another material which inhibits crack growth and improves performance. MMCs have mechanical properties similar to those of most pure metals, some alloys and most polymer-matrix composites especially at high temperatures are superior. The possibility, both the mechanical and the physical properties tailor-made by MMCs, is a unique and important feature of these materials.

Even though The technology is relatively young, there are a number of significant Applications, most notably the Space Shuttle hull braces, Space Telescope Boom Waveguide and Diesel Engine Piston. It is expected in the future metal matrix composite materials an important class of materials in numerous other commercial Applications will be.

Even though There are many metal matrix composites with widely varying There are properties some general advantages of these materials over competing ones Materials listed become. It is known that MMCs have higher strength-to-density ratios and higher Stiffness-to-density ratios with better fatigue resistance as most unreinforced Metals and some polymer-matrix composites.

numerous Combinations of matrices and reinforcements have been tried since the late 1950s began work with metal matrix composites. The most important Matrix materials are aluminum, titanium, magnesium, copper and Superalloys. Special metal-matrix composites used in engineering have been used Aluminum matrices, the boron, silicon carbide, alumina or Graphite in the form of a continuous fiber, discontinuous Fiber, a whisker or in particulate form. Magnesium, Titanium and copper are also called matrix metals with similar ones Ceramic inclusions used. additionally Superalloy matrices have been impregnated with tungsten wires to provide greater creep resistance at extremely high temperatures, like those found in jet turbine engines encounters.

The Manufacturing processes are an important part of the design process for MMCs. A considerable amount of work is being invested in this critical area and significant improvements of existing methods appear probably. Current procedures can be divided into two main categories be divided: primary and secondary Fabiraktionsverfahren. primary Fabrication methods are used to form the metal-matrix composite to create from its components. The resulting material may be in the form that is close to its desired final configuration, or it can be a considerable one additional processing require that as a secondary Fabrication is called. Some of the more popular secondary fabrication methods include forming, rolling, metallurgical bonding and machining.

A the more successful techniques for making MMCs first proposed by Toyota in 1983 for the production of pistons is, consists in an infiltration of liquid metal into a tissue or a pre-arranged fibrous configuration, as a preform or Preform is called. Often ceramic and / or organic binder materials are used, to hold the fibers in place. The organic materials will be before or during burned away the metal infiltration, which under a vacuum, a positive pressure or both. A usual used pressure infiltration technique known to she the porosity reduced in the final composite is called squeeze casting.

The squeeze casting process usually consists of putting one fiber or whisker preform into one To give cavity of a tool, to add molten metal and to infiltrate the preform with the metal by closing tool and applying high pressure with a piston. The method is typically used for nearly final molded parts with small dimensions. See Siba P. Ray and David I. Yun, "Squeeze-Cast Al ₂ O ₃ / Al Ceramic-Metal Composites", Ceramic Bulletin, Vol. 70, No. 2 (1991).

Even though Ray and Yun suggest that using ceramic matrix composites Use of preforms can be made from alumina particles having a average particle size of 0.2 Is micrometers and includes 14 to 48% open pores this disclosure on the production of ceramic matrix composites (CMCs) with very limited Toughness, ductility and machinability limited. Your construction requires the use of expensive tools and heavy wall presses that are designed to be big Withstand pressure differentials, like a 1,500 tonne press.

It is also known to squeeze metal matrix composites Casting, followed by a secondary fabrication process, as described by Njishida et al. Patent No. 4,587,707, proposed. Squeeze casting is used in this process, around a porous one shaped object of ceramic particles with a melted Infiltrate metal, which then lets it solidify. It was believed to be high pressures from 50.5 to 101.3 MPa (500 to 1000 atmospheres (15,000 to 150,000 psi)) necessary to complete the infiltration. The ceramic particles are provided by slender rods and are not uniform distributed in the matrix. Because these concentrated layers of ceramics should not be present in the metal matrix in the final product, A mechanical shaping is used to make the rods into smaller ones pieces to break and distribute them throughout the matrix. The proposed rolling or extrusion techniques contribute to the now-broken ceramic preforms spread more statistically throughout the composite; however, the result is far from a uniform distribution at microscopic Scale away. Since it is likely that the sintered ceramic rods during the mechanical forming step are broken in a non-uniform manner, For example, the resulting composite can be concentrated or agglomerated Ceramic areas containing the resulting composite properties restrict could.

Around the need for big ones To alleviate pressure requirements, most known metal infiltration techniques use size particulate Ceramics, larger than about 1 micrometer. It was not believed that the infiltration of molten metal a useful one Procedure for the production of metal-matrix composites That is, the submicron ceramic particles contain as the press size and pressure requirements are excessive and would be unrealistic. See Christodoulou et al. Patent No. 4,916,030, column 2, Lines 25-38.

Around without the restrictions and the issue of big ones Multi-ton presses have other inert gas pressure metal infiltration techniques used loose ceramic powders. See Jingyu Yang and D.D.L. Chung, "Casting Particulate and Fibrous Metal Matrix Composites by Vacuum Infiltration of a Liquid Metal and Inert Gas Pressure, Journal of Materials Science, Vol 24, pp. 3605-3612 (1989). Yang and Chung have a molten infiltration technique Metal at low pressure (6.895 to 17.24 MPa (1,000 to 2,500 psi)) which uses pressurized inert gas, to force molten metal into loose ceramic fibers or particles. particle in the size range from 0.05 to 5 microns are used. This essay teaches that by limiting the particles to a specific size range a greater porosity in the tightly packed particles can be provided because the spaces between the Particles are not filled by significantly smaller particles. It is on this porosity volume fraction resorted to enable that the low pressure force causes the molten liquid to loose Infiltrate layers of ceramic particles. Unfortunately, they tend the particles, because they are loose and not sintered, to agglomerate and while to orient statistically the metal infiltration. This has one relatively non-uniform Distribution of particles in the whole matrix result. Despite the Advantage of using less pressure therefore achieves the composite, which is not produced by the infiltration of loose particles its full ductility and strength.

Metal-matrix composites are not without further well-recognized disadvantages. The ceramic inclusions used to reinforce these composites are extremely hard and are difficult to machine using conventional techniques. This results in serious tool wear problems as the composite is machined to its final configuration. In some cases, tool wear becomes such a first problem that manufacturers resort to near-end molding techniques such as molding and squeeze casting, and the like, where the machining is kept to a minimum or scrapped altogether tet is. As reported in Charles T. Lane, "Machining Characteristics of Particulate Reinforced Aluminum", Fabrication of Particulates Reinforced Metal Composites, Proceedings of an International Conference, Montreal, Quebec, Canada, ASM International, pp. 195-201 (1990), For example, aluminum alloys reinforced with 10 to 15 micron ceramic particles used high speed steel (HSS) tools in a matter of seconds and blunted conventional and coated carbides in a matter of minutes. This paper reported that the only cost-effective machining technique for MMCs was to use polycrystalline diamond (PCD) tools at speeds up to 2,438 meters per minute. Other craftsmen had similar experience in machining MMCs, which has apparently limited their full commercial implementation.

K. Shanker et al., Composites, Vol. 23, No. 1, January 1992, pp. 47-53, and the US 5 196 273 A disclose TaC / metal-matrix composites in which the metal is aluminum or copper. Aluminum is infiltrated into the TaC preform under argon at a temperature of 1,300-1,900 ° C and a pressure of 0.1 MPa and reacts with the TaC. Copper must be infiltrated in a vacuum of <100 Pa at a temperature of 1,500 ° C to yield two continuous matrices, a ductile (Cu) and a brittle (TaC). A milling step in the production of the TaC preform is not mentioned.

T. Hanamura et al., Mat. Res. Sorc. Symp. Proc., Vol. 364, 1995, pp. 775-780 disclose γTiAl-based alloy sheets containing Al ₂ O ₃ particles produced by a combination of vacuum induction melts and direct sheet metal casting. The aluminum content of the alloy is 3 atomic%.

The article by Michael S. Nagorka et al., Metallurgical and Materials Transactions A, Physical Metallurgy and Materials Science 26A (1995) April, No. 4, p., Relates to the oxide dispersion enhancement of copper alloys. Cu-Zr and Cu-Y alloys were internally oxidized to provide about 1% by volume ZrO ₂ or Y ₂ O ₃ .

M. Otsuka et al., The 33 ^rd Japan Congress of Materials Research, March 1990, pp 13-18, certain mechanically alloyed oxide dispersion strengthened alloys containing 0.27% by mass of Y ₂ O describe contain from _3.

Accordingly, there is a need for further process developments for the production of metal matrix composites that provide superior strength and uniformity have, but also easy to machine and manufacture. There is also a need for an economic Production of metal-ceramic composites without expensive press machines or complicated processing techniques.

SUMMARY THE INVENTION

These The invention provides a metal-matrix composite and method ready for the production of metal-matrix composites. The Methods of this invention include providing a ceramic preform, the ceramic particles with an average particle size of not more than about 3 microns. These tiny ceramic particles are uniform throughout the preform distributed and are sintered together, so that at least about the half the volume of the preform of porosity is taken. The procedure includes next the steps of placing the ceramic preform in a mold and contacting them with a molten metal. The molten metal is then forced into the preform so that it penetrates these and occupies the pores. Finally will the molten metal solidifies to form a solid metal-matrix composite to build. In an important aspect of this invention, the resulting Composite material machinable and can be preferred with high speed steel (HSS) drill bit more than about 1 Minute without excessive wear the drill bit can be machined.

Accordingly, this invention combines the high strength, stiffness, and wear resistance of ceramics with the machinability, toughness, and malleability of metals. A small characteristic reinforcing material size of less than about 3 microns, and preferably less than about 1 micron, in conjunction with a large volume fraction of porosity and a substantially uniform distribution of ceramic particles in a sintered preform are all used to provide these composites. The composites of this invention provide improved room temperature and elevated temperature strengths, increased modulus and, unexpectedly, excellent machinability and ductility even at high ceramic loadings. These composites have been machined using only high speed steel (HSS) milling, drilling and tapping tools without any difficulty being experienced. There were excellent surfaces textures generated.

The MMCs of this invention exhibit high levels at room and elevated temperatures Strength, since the small reinforcing material size and the Interparticle distance meet the criteria for dispersion enhancement. The small uniform allow distributed ceramic particles, that the composite is much more like a metal than like a typical MCC behaves which allows their use in applications requiring greater ductility, toughness and moldability. The special metal infusion method of this The invention is adaptable to multiple alloy and ceramic pairings and allow a larger width to increase of the tensile modulus as the loads approach 50% by volume. Specific reinforcing ceramics and volume fractions can chosen which allow design properties to be designed, which are dictated by the application, including one high modulus of elasticity, one high strength and ductility.

In more preferred embodiments this invention proposes other critical parameters, including Preform porosities within the range of about 50 to 80% by volume, a minimum Preform compressive strength of about 3.45 MPa (500 psi) and selection of preferred ceramic and metal alloy combinations for delivery composites with light weight and high modulus. In The preferred manufacturing aspects of this invention may be used instead a piston very low gas pressures can be used to one in big Measure eased Processing of these composites without large capital expenditures. These methods can both raw blocks as well as produce near-final shaped objects under Using Press less than about 20.68 MPa (3,000 psi) of submicron size particles become. These methods are therefore inexpensive and easy to use available Starting materials and otherwise standard liquid metal infusion techniques. All these benefits can be achieved by having a very uniform distribution of small Gain ceramics used in a preform, which is an easy to infiltrate porosity having.

SHORT DESCRIPTION THE DRAWINGS

1 FIG. 4 is a photomicrograph of an alumina-reinforced aluminum matrix composite material taken at 35,000 magnifications, made by the preferred liquid metal infiltration techniques disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

By This invention will be machinable metal-matrix composites provided by an association of ceramic particles of not more than about 3 microns with molten metal in a very uniform manner descended. By using smaller ceramic particles, preferred with submicrometer size, and Distributing them in such a way in a metal matrix that Agglomeration is avoided, the composite material both a high ductility as well as a high strength, without the machine To limit machinability. In preferred embodiments of this composite are at least 80% of the ceramic particles uniform distributed on a scale of three times the particle size, and more preferably At least 90% of the ceramic particles are uniform on a scale of two times the particle size distributed. This degree of distribution of fine particles virtually eliminates size inclusions and agglomerations, which are the ductility, strength and machinability of composites.

Even though this invention all kinds of metal-ceramic composites, including Ceramic-Matrix Composites (CMCs), it is special on metal-matrix composites (MMCs) with a larger volume fraction applicable to metal as ceramic. These MMCs can come from many different Combinations of matrix material and reinforcing particles produced be in order for every application has every special required set of properties to develop.

This invention contemplates the use of ultra high strength metal matrices, including those having a yield value of 70 to 2000 MPa. Such metals include, for example, cobalt and its alloys, martensitic stainless steels, nickel and its alloys, and low alloyed hardened steels. High strength metals and alloys are also potential candidates for the matrices of this invention, including tungsten, molybdenum and its alloys, titanium and its alloys, cast copper alloys, bronzes, copper species, niobium and its alloys and superalloys containing nickel, cobalt and iron. Metals and alloys with medium strength can also including hafnium, austenitic stainless steels, brass types, aluminum alloys between the 2,000 and 7,000 series, beryllium rich alloys, depleted uranium, magnesium alloys, silver, zinc die cast alloys, copper alloys, copper-nickel alloys, copper-nickel-zinc alloys and other metals with a yield value of about 40 to 690 MPa. Finally, this invention optionally employs low strength, low density alloys for the matrices of this invention. Such metals are represented by gold, cast magnesium alloys, platinum, 1000 series aluminum alloys, lead and its alloys, and tin and its alloys. These materials have a yield value of only about 5 to 205 MPa. Most desirably, this invention uses light weight metals and those that are relatively inexpensive and widely available, such as aluminum, lithium, beryllium, lead, tin, magnesium, titanium, and zinc, and metals that have superior electrical properties, such as copper , Silver and Gold. All of these selected metals can be provided in commercially pure or alloyed form. Specific alloys that have been found to have particular utility in MMCs include Al-1 Mg-0.6 Si, Al-7 Si-1 Mg, Al-4.5 Cu, Al-7 Mg-2 Si and Al-Fe-V-Si.

Even though Alloys and commercially pure metals can be used to producing the matrices of this invention is a pure metal the matrix of choice, since ceramic dispersion reinforcement is all what kind of improved properties is required. A pure metal offers across from Alloys also increased corrosion resistance and eliminates the effects of aging of precipitation. Reinforce pure metals also the efficiency at elevated Temperature by increase the homologous melting point compared to comparable alloys. After all Pure metals eliminate the difficulties associated with a micro-demixing and a macro-mixing of the alloying elements in non-eutectic Alloys during the solidification are connected.

The Ceramic or Second Phase Components of Metal-Matrix Composites of this invention are desirably of a size that Does not interfere with the machining by HSS tools. It was discovered that machinability is only maintained when these ceramic particles are less than about 3 microns in size, Although this invention preferably has a size range of about 0.01 to 0.5 micrometers used. The ceramic particles should over the Time and at the temperature of the particle production process and the ambient conditions in use thermally and chemically stable be.

These Ceramic particles should not decompose at high temperature still react with the metal matrix. If they tend to be in diffusing the matrix, the diffusion of the reinforcement must be slow, so the strength of the composite is not serious deteriorated. Ultrafine reinforcing particles with a volume fraction of about 20 to 40% are particularly advantageous in obtaining composites with improved Young's modulus, improved ductility and machinability.

exemplary Second-phase ceramic candidates include borides, carbides, oxides, Nitrides, silicates, sulfides and oxysulfides of elements that are under Formation of ceramics can react, including, without but limited thereto to be, transitional elements the third to sixth group of the periodic table. Especially useful Ceramics-forming or intermetallic compounds forming constituents Aluminum, titanium, silicon, boron, molybdenum, tungsten, niobium, vanadium, Zirconium, chromium, hafnium, yttrium, cobalt, nickel, iron, magnesium, Tantalum, thorium, scandium, lanthanum and the rare earth elements. more exotic Ceramic materials include titanium diboride, titanium carbide, zirconium diboride, Zirconium disilicide and titanium nitride.

Ceramics-based ceramics may also be useful as a ceramic phase, including natural and synthetic diamonds, graphite, fullerenes, diamond-like graphites, etc. Certain ceramics are for their availability, ease of manufacture, low cost, or exceptional strength-inducing properties most desirable. These include Al ₂ O ₃ , SiC, BaC, MgO, Y ₂ O ₃ , TiC, graphite, diamond, SiO ₂ , ThO ₂ and TiO ₂ . These ceramic particles desirably have a length to width ratio of not more than about 3: 1 and preferably not more than about 2: 1, but may be present as fibers, particles, beads and flakes, for example. However, particles are preferred because of machinability.

Alternatively, the ceramic reinforcements of this invention may have aspect ratios ranging from equiax to platelet and ball-like configurations. The particle size distribution may range from monosize to a Gaussian distribution or a wide tail distribution at fine sizes. These particles can be prepared using a variety of wet and dry techniques ken, including ball milling and air abrasion.

The preferred binders used in conjunction with the ceramic reinforcements can be used lock in: inorganic colloid and organic binders, such as Sintering binder, low temperature (QPAC) and high temperature colloid binder. Such binders include polyvinyl alcohol, methyl cellulose, colloidal alumina and graphite.

Metal matrix composites, the according to this Invention and one or more of the above metals, one or more of the above alloys and one or more Ceramic particles can contain too many useful ones Configurations for a variety of applications are processed. Some of the more interesting Applications are listed below in TABLE I.

TABLE I: Representative metal-ceramic composites and potential applications

The Performance of the resulting composites of this invention closely related to the uniformity of used in the preferred metal infiltration process preform connected. These preforms can by a variety of processes including sediment casting, injection molding, gel casting, slip casting, isopressing, Ultrasonic techniques, filtering, extruding, pressing and the like. Preferably, colloidal processing is used to preform manufacture. The addition of volatile Fabrics and a controlled agglomeration of the slurries can used to measure the particle volume fraction within the desired Set area.

After producing a green preform, the preform is preferably dried or fired. This can be accomplished by microwave processing, freeze-drying or air / inert gas burning. Test bars can also be made together with the preform so that a determination of the rupture modulus or properties can be evaluated prior to pressure infiltration. A Target compressive strength of at least about 3.45 MPa (500 psi) and preferably about 4.83 to 8.274 MPa (700 to 1200 psi) is desirable for the sintered preform.

The Preforms of this invention are ideally made with liquid metal pressure infiltrated to produce ingots or shaped articles. The pressure infiltration can be any type of liquid metal infiltration (LMI) process lock in, including: Inert gas printing techniques, squeeze casting and molding etc in one most preferred method is an inert gas pressure infiltration used. This procedure includes the key steps: Evacuating the Preform before infiltration, suitable pressure control for infiltration without preform breaking and directional solidification under pressure, to bring about a hardening shrinkage.

In A mass production environment could be the production of raw bars with big ones Size a forge processing to usual Product forms follow. Pressure infiltration coupled with forging offers the possibility high performance composite manufacturing at low cost for one big variety of structural applications. The forging can be such Include processes such as extrusion, rolling, forging, etc. A Net shape processing can also be used, including: molding and Squeeze casting. In these latter methods, large rough bars because of the inherent stability the claimed composite materials melted again and processed in the liquid state Become to near-endform components to produce. Approximate Properties for an aluminum and magnesium matrix MMC, by the preferred Process of this invention are described below in included in TABLE II.

TABLE II: Approximate physical properties of dispersion strengthened aluminum and magnesium

The Applicants have the preferred loading ranges for the MMCs evaluated this invention and have found that a 15th vol .-% ceramic loading the module of commercially pure aluminum and magnesium improved by about 30%. 25 vol.% Ceramic particles Improves the module by about 50 to 60% and a 55 vol .-% ceramic loading improves the module by about 100%, but the ductility begins to suffer. Ceramic loadings with up to 45% by volume generated MMCs, those with high-speed steel without significant wear were edited. It was further noticed that when the ceramic particles about 3 microns exceeded, the machinability of the MMC dramatically decreased. Regarding the Volume fraction was further noted that ceramic loadings of more than about 50% ductility of the composite significantly reduced and loadings significantly below 15% by volume did not produce any significant modulus improvement. Lower loadings were also difficult to infiltrate as the preforms too weak to withstand infiltration pressures without breaking.

The The present invention will be further understood with reference to the following examples described.

Example I

A composite material was prepared with a matrix of commercially pure Al that included 25% by volume Al ₂ O ₃ having an average particle size on a population basis of about 0.2 microns. As a preliminary step, the starting materials were weighed as follows:
Reinforcement: A-16SG, calcined Al ₂ O ₃ , 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, Al2O, high temperature coating / binder, Nyacol Products, Inc., 86.0 grams.

These Mixture was made using the following milling parameters in one Mill united: Slurry solids content of 10% and mill filling level of 30%. The slurry approach was ground for about 23 to 25 hours, removed from the mill and in a pressure filtration unit arranged. The slurry was filtered at 2.41 MPa (350 psi) for about 36 to 60 hours. When When the filtration was complete, the green preform was removed from the filtration unit away. It was measured to have dimensions of one diameter about 4.9 cm by 12 cm in length had. The green Preform had a reinforcement loading of about 22% by volume. The green The preform was then dried at ambient conditions until a Weight loss of at least about 25 wt .-% was achieved. This lasted about five Days.

The dry preform was then placed in an oven and fired according to the following schedule:

The fired preform had a loading of about 25% by volume sintered ceramic particles. It was removed and checked, and a weight loss of about 40% by weight was noted. This weight loss ensured that all filler material had been removed. A mild steel infiltration crucible was prepared by coating with a graphite washcoat 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 then inserted into the lined crucible and a preform support rod was inserted to prevent floating. The crucible was then introduced into the pressure infiltration unit, which was a custom-made one. The pressure infiltration unit was evacuated and then preheated using the following heat cycle:

Approximately 650 grams of commercially pure aluminum (99.9% aluminum, granules 2 to 5, available from Alcoa) were then melted in an electric resistance oven and with Flux No. 770 Cover Flux, available from Asbury Graphite Inc., covered. The infiltration unit was then returned to argon filled, the crucible was removed from the pressure infiltration unit, and the molten alloy was poured into the crucible. The crucible was then added to the pressure infiltration unit and it became evacuated again. After evacuation, the unit was treated with argon in about 40 to 80 seconds under a pressure of about 14.8 MPa (2,150 psi) and five Minutes kept. The unit was then vented and the crucible was opened a water cooled Quenching plate placed at the bottom of the pressure infiltration unit. The unit was for the solidification again under a pressure of 6.895 MPa (1,000 psi). They left the Cool mixture for about an hour, until she solidified herself directionally. The sample was removed from the pressure infiltration unit, the crucible was cut away and the alloy insert became away.

A fracture surface of a sample of the above composite was visually inspected under a scanning electron microscope at 35,000X. The micrography is in 1 shown. 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.

The following mechanical properties were measured after two samples were removed from the resulting ingots:
Practical yield value, MPa (ksi) = 170.3 (24.7)
Tear strength, MPa (ksi) = 331 (48.0)
% Elongation = 6.0
1.00 SR, short bar fracture toughness = 18.1 MN · m ^-3/2 (16.5 KSi (IN) ² )

Other samples were extruded at 440 ° C (825 ° F) and additional samples were prepared for hardness, tensile and fatigue properties, with the following results: Hardness As extruded Rb 57 As solution-treated (940 F / 1 h / WQ) Rb 59 Solution treated (940 F / 1 h / V1 / Q) plus age (400 F / 2 h / AC) Rb 56

thermosetting

tensile

smoothing fatigue

Example II

Using a population-based Al-2.5 Mg matrix with a volume fraction of 25 Al ₂ O ₃ particles having a mean particle size of 0.2 microns, a composite was made using the same procedure as described in Example I. Material was made in the form of a 0.249 cm x 48 cm x 24 cm plate, except that the matrix included 5052-H32 Al-2.5 Mg alloy. The procedure parameters were identical, except that the Al-2.5 Mg alloy was substituted for the commercially pure aluminum. During the melting of the alloy, no protective flux was used and the holding temperature during the infiltration was about 695 ° C. Using the same test methods as disclosed in Example I, the following properties were obtained:
Sound modulus, Pa (MSI) = 109.3 Pa (15.85)
Lateral speed = 0.318
Density (g / cm ³ ) = 3.023

Example III

A composite material was prepared which included a matrix of commercially pure Al including 40% by volume Al ₂ O ₃ having an average particle size of 0.2 microns on a population basis. The starting materials of Example I were the same except for the fact that an organic binder, AIR VOL 540, polyvinyl alcohol, from Chemicals Group Sales of Air Products and Chemical, Inc., was used and a colloid chemistry adjustment was made using the Addition of nitric acid, 69.0 to 71.0%, BAKER ANALYZED Reagent, ENT ₃ from VWR Scientific included. As in the previous examples, the dried ingredients were weighed as follows:
Reinforcement: A-16 SG calcined Al ₂ O ₃ , 633.0 grams.
Carrier: POLAR distilled water, 920.7 grams.
Filler: Micro 450 (M-450) graphite, 104.5 grams.
Organic binder: (6 wt.% Solution in water), AIR VOL 540, 30.1 grams.
Colloid Chemistry Adjusting Agent: Nitric Acid, 0.4 ml.

The Mixture was in a similar Milling process, as used in Example I, with the following grinding parameters: slurry solids content of 17.5% and mill fill level of 25%. The slurry batch was ground for about 23 to 25 hours, removed from the mill and placed in a pressure filtration unit given.

The slurry was filtered for about 20 to 30 hours at 350 psi. As the filtration was finished, the green was Preform, 37 vol.% Ceramic, removed from the filtration unit. It was measured to have dimensions of 4.9 cm diameter x 4 cm in length. The green The preform was then dried at ambient conditions until a Weight loss of at least 23% by weight had been achieved. This lasted about five Days.

The dried preform was then placed in an oven and fired according to the following scheme:

The fired preform had a loading of about 40% by volume sintered Ceramic particles on. She was removed and checked, and a weight loss greater than about 15% by weight was found.

A mild steel infiltration crucible was then prepared according to the same procedure as described in Example I, introduced into the infiltration unit and evacuated. The unit was then preheated using the following heat cycle:

Approximately 600 grams of commercial pure aluminum, as in Example I above were then melted, and an inert gas infiltration was used to make a composite material essentially according to the procedures of Example I.

The following mechanical properties were measured:
Material condition: as cast
Sound modulus, Pa (MSI) = 122 (17,7)
Lateral speed = 0.288
Density (g / cm ³ ) = 3.113
Material condition: extruded
Tear strength, MPa (ksi) = 448 (65)
Elongation = 4

hardness

• 70 Rb

Example IV

It became a composite material with a matrix of commercial pure Mg, the 30 vol .-% MgO ceramic particles with a average particle size of about 0.8 microns (about 0.2 microns after milling) included. The starting materials used were the same as those used in Example I, with the following exceptions: The reinforcement included MAGCHEM 20-M, magnesium oxide technical grade from Martin Marietta Magnesia Specialties, Inc .; the carrier used was denatured ethanol from E.K. Industries, Inc .; the organic one Binder was Bulls Eye Shellac, clear sealer and finish, from Williams Zinsser & Co., Inc., and the matrix was commercially pure magnesium, 99.8 Wt% magnesium, 0.453 kg (1 pound) rods, 3.3 cm (1.3 inches) diameter x 30 cm (12 inches) in length.

The starting materials were weighed as follows:
Reinforcement: MAGCHEM 20-M Magnesium Oxide, Martin Marietta Magnesia Specialties, Inc., 232.3 grams.
Carrier: POLAR distilled water, 727.2 grams.
Filler: Micro 450 (M-450) graphite, 98.6 grams.
Organic binder: Bulls Eye Shellac, 116.4 grams.

These Mixture was made using the following milling parameters in one Mill united: Slurry solids content of 10% and mill filling level of 25%.

The slurry batch was according to the milling process of Example I ground. When the filtration was over, the green preform removed from the filtration unit. It was measured that they are dimensions of about 4.9 cm diameter × 10 cm length had. The green Preform had a reinforcement loading of about 26 vol.% and was then dried at ambient conditions, until a weight loss of at least about 25% by weight has been achieved was. This lasted about five Days.

The dried preform was then placed in an oven and fired according to the following scheme:

The fired preform had a loading of about 29% by volume sintered Ceramic particles on. She was removed and checked, and a weight loss of at least about 34% by weight was found.

An infiltration crucible was prepared and prepared essentially as described in Example I. About 300 grams of matrix magnesium alloy was placed on top of the preform and preform support rod. The crucible was introduced into the pressure infiltration unit, the unit was evacuated and refilled to an argon pressure of about 300 psi. The unit was then preheated using the following heat cycle:

To the two-hour Stop at about 705 ° C the unit was evacuated. After the evacuation, she was with Set argon under a pressure of about 14.82 MPa (2,150 psi) and five minutes held. Directional consolidation and removal steps were essentially the same as the ones above at example I have been described. Samples were made and a hardness value of 65 Rb was measured. The hot hardness values essentially showed a parallel trend as with the aluminum matrix samples.

Test on machine machinability

There were samples of the Al / 25 vol .-% Al ₂ O ₃ (Example I); Al / 40 vol.% Al ₂ O ₃ (Example II); Al-2.5 Mg / 25% by volume Al ₂ O ₃ (Example III); and Mg / 30% by volume of MgO (Example IV).

Each of these samples was subjected to the following machining operations with the noted results:
Surface milling and finish milling was performed with HSS tools. There was no difficulty in using speeds of about 0.66 m / s (130 sfm) and up to about 0.63 cm (1/4 inch) chip removal. The surface finish was good.

The Drilling was done without any problem with uncoated regular HSS twist drills. The Drilling was accomplished at about 0.51 m / s (100 sfm). The holes with a diameter of about 0.85 mm (1/32 inch) to a diameter of about 1.59 cm (5/8 inches) were without apparent limitation of Depth achieved.

The Internal threading was performed with an uncoated 3-groove HSS tap, from Hand on sizes in the area from about 0.32 cm (1/8 inch) to about 1.9 cm (3/4 inch) coarse and fine Cut threads. You came up no difficulties.

Samples prepared from the Al / 25 vol.% Al ₂ O ₃ and the Al-2.5 vol.% Mg / 25 vol.% Al ₂ O ₃ were spun on a lathe using a solid carbide Tool cutting plate with about 1.78 m / s (350 sfm) turned. The tool bit removed at least 98.3 ^cm3 (6 cubic inches) of material and operated for at least three hours without difficulty.

An Al / 40 vol.% Al ₂ O ₃ sample was lathe turned on a lathe using a HSS tool cutting plate at about 1.75 m / s (350 sfm). The tool bit removed at least about 49.2 ^cm3 (3 cubic inches) of material and operated at least two hours without difficulty. Good to excellent surface finishes were obtained.

Comparative example V

The Drilling was performed using a 356-T6 Al matrix, the with 20% by volume of SiC (average particle size 10 to 15 microns) (DURALCAN F3A.20S) was. Drilling was done with a 0.63 cm (1/4 inch) HSS drill bit performed using a hand drill. The drill bit penetrated approximately 0.63 cm (1/4 inch) and was blunted to the point where it was necessary again to sharpen.

An attempt was made to cut this material using a band saw. The saw penetrated about 0.63 cm (1/4 inch) and then stopped. Both the hand drilling and band sawing techniques were later repeated with difficulty on an Al / 25 vol% Al ₂ O ₃ sample of Example I.

Comparative Example VI

A additional Comparative sample was prepared by gas pressure infiltration of loose SiC ceramic powder with a average particle size of 10 Micrometers and commercially pure liquid Mg metal. The resulting Mg / 40 to 50 vol% SiC composite was on a lathe using a solid carbide tool cutting plate Turned. The lathe just cut for a few seconds, then the insert began to dull and pushed the material only.

Comparative example VII

Under Using the same technique as described in Example VI, was another comparison sample with an average SiC particle size of 3 Made of micrometers. An experiment was made, the resulting Saw Mg / 40 to 45 vol.% SiC composite with a band saw. The band saw held fast within about 10 to 15 seconds without significant Intrusion into the matrix.

Out From the foregoing, it can be appreciated that this invention high performance machinable metal matrix composites Module and metal infiltration techniques for the production of these composites provides. Critical parameters were discovered which the necessary areas of the volume fraction of porosity and the particle size distribution map that for low pressure metal infiltration and optimum mechanical properties required are. Although various embodiments have been explained are, this happened for the purpose of the description and not to limit the invention. Various Variations that will become apparent to those skilled in the art are within the scope of this invention, which is described in the appended claims.

Claims (21)

A method of making a metal-matrix composite, comprising the steps of: providing a ceramic preform with submicron ceramic particles and sintering the ceramic together particles; Arranging the ceramic preform in a mold; Contacting the ceramic preform with a molten metal; Causing the molten metal to penetrate into the preform; and allowing the molten metal to solidify to form a metal-matrix composite; wherein the metal matrix composite is machinable with a high speed steel drill bit, characterized in that, in a first step, a colloidal slurry of ceramic particles in a liquid is subjected to a milling step to provide a colloidal slurry of ceramic particles in which Particles have a particle size of not more than 1 micrometer; and then separating the ceramic particles from the liquid to provide a ceramic preform having a uniform distribution of submicron ceramic particles. Method for producing a metal-matrix composite according to claim 1, in which at least 80% of the ceramic particles are uniform a scale of three times the average particle size are. Method for producing a metal-matrix composite according to claim 2, in which at least 90% of the ceramic particles are uniform a scale of twice the average particle size are. Method for producing a metal-matrix composite The claim of claim 1, wherein the step of causing the molten one of Metal penetrates into the preform, is accomplished by pressure infiltration. The method of claim 4, wherein the ceramic preform 50 to 85% porosity in terms of Volume includes. The method of claim 5, wherein the ceramic preform from 60 to 80% porosity in terms of Volume exists. The method of claim 4, wherein the composite material a tensile modulus at least 30 to 200% greater than is the tensile modulus of the metal. The method of claim 1, wherein the step of Providing a ceramic preform for filtering, extruding, Pressing or slip pouring a precursor of the particles to produce a green preform. The method of claim 1, wherein the step of Causing infiltration of molten metal which causes the molten metal through a pressurized gas in the Pores of the preform pressed into it becomes. The method of claim 9, wherein the under pressure standing gas has a pressure of 6.895 to 20.685 MPa (1000 to 3000 psi) and the preform has a compressive strength of at least 3,448 MPa (500 psi). Process according to claim 1, in which the molten one Metal is forced into the preform by pressure infiltration to cause the molten metal in the pores of the preform penetrates without breaking the preform. The method of claim 11, wherein the ceramic particles are: an oxide, boride, nitride, carbide, carbon, a silicide, sulfide, Oxysulfide or a mixture thereof. The method of claim 11, wherein the colloidal slurry the ceramic particles with up to 70 vol .-%, based on the volume on dry ingredients, a filler, binder or a mixture of the same is mixed. The method of claim 10, wherein the under pressure standing gas is an inert gas with a pressure of 10.34 MPa to 17.23 MPa (1500 to 2500 psi). The method of claim 11, wherein the metal-matrix composite has an approximate final shape having. Process according to claim 1, in which the molten one Metal selected from the group is made of: Al, Li, Be, Pb, Ag, Au, Sn, Mg, Ti, Cu, Zn or one Mixture of the same exists. The method of claim 1, wherein the step of Provision of a preform includes: pressure filtering a precursor the ceramic particle with a graphite filter in the separation step, Suspend the filtered particles with a graphite filler and an inorganic binder to form a green preform; and burning the green Preform to the filler to remove, whereby a portion of the ceramic particles sintered together becomes. The method of claim 9, wherein the step of into depression the evacuation of a gas from the preform by an applied Vacuum and pushing in of the molten metal in the pores of the preform with an under Comprises pressurized argon-containing gas. A method according to any one of claims 1 to 18, wherein the particles are Al ₂ O ₃ and the molten metal is Al. A method according to any one of claims 1 to 19, in which the particles have a particle size of 0.01 to 0.5 microns exhibit. Metal-matrix composite comprising a uniform distribution of alumina particles having an average particle size of not more than 1 micron and aluminum, which is substantially uniform with the alumina particles is distributed, wherein at least 80% of the Alumina particles evenly on a scale of three times the average particle size are, with the alumina ceramic loading 15 vol.% To 50 vol.%.