The invention relates to a process for the preparation of complex-shaped ceramic-metal composite articles, preferably thin, complex-shaped ceramic-metal composite articles such as computer hard disks and computer hard disk drive components

Ceramics are typically known as low-density materials with high hardness and stiffness, however, their bπttleness limits their usefulness Furthermore, ceramics are typically formed by creating a densified compact that requires significant and expensive grinding to achieve a final shape, due to the large amount of shrinkage that occurs during densification of the compact Metals are typically non- brittle, non-breakable mateπals, however, they lack some of the desirable properties of the ceramics, such as high hardness and stiffness Therefore, combining a ceramic with a metal can create a composite material that exhibits the properties of a ceramic and a metal

Processes for making ceramic-metal composites using ceramic preforms are known in the art U S Patent 4,605,440 discloses a method for making boron-carbide-reactive metal composites compnsing co-dispersing the boron-carbide and reactive metal powders and consolidating the co- dispersed powders into a green body and reacting the green body at temperatures of 800°C to 1400°C for varying times, such that the desired composition is produced U S Patent 5,308,422 discloses a process for making ceramic-metal composites involving forming layers of ceramic mateπal, sintering the layers of ceramic material into a porous ceramic compact, and then infiltrating the porous compact with a metal by immersing the porous body in a bath of molten metal Both processes involve several costly and time-consuming processing steps, such as formation of the porous compact or green body and sintering of the compact Furthermore, sintering can cause considerable shrinkage of the final product, which is undesirable U S Patent 4,834,938 discloses that it is possible to create ceramic metal composite articles having intricately shaped internal passages or capillaries or hollow portions This process discloses articles initially created in their "net shape" form, and processed without significant shπnkage to form a ceramic-metal composite article with an internal hollow cavity For example, an insert body of metal is formed having an external surface corresponding to the internal cavity of the final composite article Next, a porous compact of ceramic is formed around the metal insert by assembling the metal insert and ceramic mateπal in an appropriately shaped die and subjected to isostatic pressure The article is then heated to a temperature such that the metal insert mateπal infiltrates into the porous ceramic compact, forming a ceramic-metal composite article with an internal hollow cavity This process creates products with internal cavities, and, additionally, involves several costly and time-consuming processing steps What is needed is a process for making solid yet complex-shaped ceramic-metal composite articles that are intricate in shape or that have areas of complex geometry, wherein solid refers to an article that has no completely internal cavities or internal hollow areas A process is needed that allows

the formation of thin, solid, complex-shaped ceramic-metal composite articles with close tolerances What is also needed is a more cost efficient, faster method of making such complex-shaped composite articles, while still maintaining the desired physical properties, such as low density, high stiffness, high strength and toughness The invention is a process for the preparation of a solid, complex-shaped ceramic-metal composite article, comprising a) forming a shaped metal body, b) contacting the shaped metal body with ceramic material to form a layer of the ceramic mateπal on one or more surface(s) of the shaped metal body, and c) infiltrating the ceramic material with the metal of the shaped metal body such that a solid, complex-shaped ceramic-metal composite article comprising one or more metal phases and one or more ceramic phases is formed, wherein the article has substantially the net shape of the shaped metal body The process of the invention allows the preparation of solid, complex-shaped ceramic-metal composite articles with little or no shrinkage or change in shape of the article after the initial shaping of the metal, while utilizing a more cost efficient, faster process and still maintaining the desired physical properties such as low density, high stiffness, high strength and toughness The process of the invention does not require time-consuming steps such as sinteπng or pressing the ceramic mateπal into a form or shaped body

The process of the invention is used to prepare ceramic-metal composite articles of complex shape comprising one or more metal phases and one or more ceramic phases Preferably, the process can be used to prepare thin ceramic-metal composite articles of complex shape The complex-shaped articles of this invention are solid articles, wherein solid article refers to an article that has no completely internal cavities which have been defined solely by an external surface of the formed metal body The solid complex articles of this invention may have areas of complex geometry such as blind holes, through holes and complex radii or curvature The complex-shaped ceramic metal composite article preferably comprises at least three phases Preferably, each of the phases is present in an amount of at least 2 volume percent, based on the volume of the multi-phase ceramic-based mateπal The ceramic-metal composite article preferably has a residual free metal content of 2 volume percent or greater The ceramic-metal composite article preferably has a residual free metal content of 75 volume percent or less, more preferably 50 volume percent or less, and even more preferably 25 volume percent or less The process of this invention may be utilized to produce ceramic-metal composite articles in which the metal infiltrates and essentially fills all of the pores of the porous ceramic Preferably, the ceramic-metal composite article has a theoretical density of 98 percent, and more preferably 99 5 percent, wherein percent theoretical density is 100 times the ratio of the composite body bulk density over the theoretical density of the material, and theoretical density is the density of material with no porosity The ceramic-metal composite article preferably has a thickness of 0 25 micrometers (0 25 x 10 ' mm) or greater, more preferably 1 micrometers ( 1 x 10 ' mm) or greater, and even more

preferably 5 micrometers (5 x 10 ' mm) or greater The ceramic metal composite article preferably has a thickness of 2 mm or less, more preferably 1 mm or less, and even more preferably 0 5 mm or less The ceramic-metal composite articles preferably have an elastic modulus high enough to prevent or reduce the incidence of warping, sagging, fluttering or resonating duπng handling and use Preferably, the ceramic-metal composite article demonstrates an elastic modulus of 100 GPa or greater, more preferably 150 GPa or greater, and even more preferably 200 GPa or greater The complex ceramic-metal composite articles of the invention preferably demonstrate flexure strength high enough to impart shock resistance and resistance to damage during handling and usage The ceramic-metal composite articles of the invention preferably demonstrate a flexure strength of 250 MPa or greater, more preferably 350 MPa or greater, and even more preferably 450 MPa or greater If electrical resistivity is a desired property, the ceramic-metal composite articles of the invention preferably have an electπcal resistivity low enough to prevent a build-up of static electπcity Preferably, if low electrical resistivity is a desired property, the composite article of the invention demonstrates an electrical resistivity 10 ' ohm-cm or less, more preferably 10 ohm-cm or less and even more preferably 10 ⁵ ohm-cm or less The metals useful in this invention are selected based on their capability of chemically reacting or wetting with a chosen ceramic mateπal at elevated temperatures such that the metal penetrates into the pores of the ceramic Selected metals can be taken from Groups 2, 4, 5, 6, 8, 9, 10, 13 and 14 using the new notation of the Periodic Table as published in The Handbook of Chemistry and Physics. CRC Press, New York, New York, U S A (1995 1996), and alloys thereof Preferable metals for use herein include silicon, magnesium, aluminum, titanium, vanadium, chromium, iron, copper, nickel, cobalt, tantalum, tungsten, molybdenum, zirconium, niobium or mixtures and alloys thereof More preferred metals are aluminum, silicon, titanium and magnesium or mixtures and alloys thereof Aluminum and alloys thereof are preferred because they exhibit high toughness, good electrical conductivity and machinability, and have good wettability with a chosen ceramic, such as boron carbide, for example Aluminum is best employed as an alloy which provides improved stiffness relative to pure aluminum Alloys of aluminum with one or more of Cu, Mg, Si, Mn, Cr, Zn are preferred Alloys such as AlCu, AlMg, AlSi, AlMnMg and AlCuMgCrZn and mixtures thereof are more preferred Examples of such alloys are 6061™ alloy, 7075™ alloy, and 1350™ alloy, all available from the Aluminum Company of America, Pittsburgh, Pennsylvania The ceramics useful in this invention are chosen based on their chemical reactivity with the chosen metal at elevated temperatures so as to increase the penetration of the metal into the pores of the ceramic Preferable ceramics for use herein include borides, oxides, carbides, nitrides, sihcides or mixtures and combinations thereof Examples of combinations of ceramics include borocarbides oxynitπdes, oxycarbides and carbonitπdes More preferred ceramics are boron carbides, silicon carbides, titanium diboπdes and silicon nitπdes The preferred ceramic mateπal is boron carbide, because it has a desirably low density and high stiffness, along with excellent wetting characteristics when in contact with a selected metal The ceramic is preferably in powder form in order to facilitate the

contacting of the ceramic with the shaped metal body The ceramic powder used to form the composite material typically contains metal chemically bonded to the boron, oxygen, carbon, nitrogen or silicon of the ceramic The powdered ceramics are preferably crystalline mateπals having grains that are 0 1 micrometers (0 1 x 10 ³ mm) or greater The powdered ceramics are preferably crystalline materials having grains that are 50 micrometers (50 x 10 ³ mm) oi less, more preferably 5 micrometers

(5 x lO 'mm) or less, and even more preferably 1 micrometer ( 1 x 10 ³ mm) or less The crystalline particles may be in the shape of equiaxed grains, rods, or platelets

Examples of preferred ceramic-metal combinations for use in forming multi-phase ceramic metal composite articles comprises B ₄ C/A1, SiC/Al, A1N/A1, TiBVAl, Al.O/Al, SiBx/Al, S1 ₃ N/AI, SiC/Mg, S1C/T1, SiC/Mg-Al, SiBx Ti, B C/Nι, B ₄ C Tι, B ₄ C/Cu, Al ₂ 0,/Mg, Al,0,/Tι, TiN/Al, TiC/Al, ZrByAl, ZrC/Al, A1B, AI, A1B./A1, A1B _M Q/A], A1B, ₂ /Tι, A1B ₂₄ C ₄ /Tι, T1N/T1, T1C T1, ZrO Ti, TιB B ₄ C/Al, S1C/T1B AI, T1C/M0/C0, ZrC/ZrC/ZrB2/Zr, T1B/N1, T. Cu, T1C/M0/N1, S1C/M0, T1B/T1C/AI, TiB/T C/Ti, WC/Co, and WC/C0/N1 The use of the subscript "x" represents that the compound can have varying stoichiometry More preferred ceramic-metal combinations comprise B ₄ C/A1, SiC/Al, SιB ₆ /Al, TιB,/Al and SiC/Mg Most preferably, the mateπals forming the complex- shaped ceramic-metal composite article of the present invention are chemically reactive systems such as aluminum-boron-carbide In these chemically reactive systems, the metal component, after infiltration, can be depleted to form ceramic phases that modify article properties such as hardness The aluminum boron-carbide composite material includes at least one boron-carbide-containing phase and at least one aluminum-containing phase Additionally the phases may be admixed with a filler ceramic The filler provides material for the finished article that does not adversely affect the desired properties of the ceramic-metal composite article Filler can be selected from borides, carbides, nitrides, oxides silicides, and mixtures and combinations thereof The filler ceramic is preferably employed in an amount from 1 to 50 volume percent, based on the volume of the multi-phase ceramic-based material The aiuminum-boron-carbide composite article preferably includes the phases of B ₄ C, A1B„C ,

A1 _M BC, A1B ₂ , AIB,,, AlB.-C,, A1 ₄ B, ,C ₄ and free metal Al The most preferred material is a multi-phase material made of B ₄ C, Al, and at least three other ceramic phases, preferably, A1B, ₄ C ₄ , A1,BC A1 ₄ BC, and AIB, The B ₄ C grains are preferably surrounded by aluminum boride and aluminum-boron-carbide In other words, the composite article has a continuous ceramic network of aluminum boron, boron carbide, and aluminum-boron-carbide

The starting materials used for the process of the invention depend upon the product desired In any embodiment, the metal and ceramic must be selected so as to facilitate infiltration Infiltration is the process by which a metal, upon melting, forms a solid-liquid interface with a ceramic, with the metal as the liquid and the ceramic as the solid, and the metal moves into the pores of the ceramic material by capillary action The wetting contact angle, as defined by Young's Equation, at which infiltration occurs is preferably less than 90 degrees, more preferably less than 45 degrees, and most preferably less than 30 degrees

The process of the invention involves a series of steps to be performed in order to achieve a ceramic-metal composite article of complex shape comprising one or more metal and one or more ceramic The first step comprises forming the selected metal into a desired article shape This step can be accomplished by a variety of ductile metal-forming processes as discussed hereinafter The ceramic material is then contacted with the surface(s) of the shaped metal body The ceramic powder can be contacted with the shaped metal body by any means which results in the formation of a layer of the ceramic material on the surface(s) of the shaped metal body Preferably, the chosen ceramic powder is mixed into a slurry to allow it to be easily contacted with the shaped metal body Once the ceramic material is contacted with the shaped metal body, the next step involves infiltrating the ceramic material with the metal of the shaped metal body through a process of heating the metal until it is molten, wherein the metal penetrates the pores of the ceramic If desired, after infiltration a heat treatment may be performed to impart certain other mechanical properties to the final complex-shaped ceramic-metal composite article

In performing the first step of the process, the selected metal is formed into the near net finished article shape Any metal-forming process or processes may be used which allows the formation of complex-shaped parts at or near net size and shape Such metal-forming processes are well known in the art, for example, casting, molding, spinning, extrusion, drawing, forging, powder metallurgy, stamping, punching, rolling, mechanical machining and chemical machining See, for example, S Kalpakjian, Manufacturing Engineering and Technology 2d Ed Addison-Wesley Publishing Co , 1992 Preferred metal forming processes include those that form thin metal sheet, shapes from said sheet, and complex thin walled shapes (for example, tubes) Examples of said preferred processes include spinning, extrusion, stamping, punching, rolling and chemical machining

More preferably, the shaped metal body is formed from a thin metal sheet, wherein the thin sheet is a sheet that is less than 6 mm thick, preferably less than 2 mm. more preferably less than 1 mm, and even more preferably less than 0 5 mm thick Preferably, the metal sheet is formed by a flat rolling process Flat rolling to form a metal sheet is a process which reduces the thickness of a long piece of metal by compressive forces applied through a set of rolls Rolling processes can also form, for example, seamless tubes and rings having a complex cross-sectional geometry The metal sheet can also be formed into more complex shapes by any number of metal-forming processes such as stamping, drawing, chemical machining, spinning, punching and combinations thereof Preferably, stamping imparts the desired end geometry to the article by shearing and compressing a metal blank (that is metal sheet) in a die and then removing said part from the die Another preferred process of forming the shaped metal body from a thin metal sheet is chemical machining Chemical machining is the removal of metal by chemical dissolution as opposed to mechanical means The shape is formed from the metal sheet by a photochemical blanking technique analogous to photolithography techniques in forming printed wiring boards Preferred shapes created from these processes include flat, thin, rounded disks of metal such as computer hard disks, suspension arms for computer hard disk drives, other hard disk dπve

components and other complex-shaped articles, such as those that require a combination of high stiffness, strength, toughness and thinness

Before contacting the shaped metal body with a ceramic, the metal may be cleaned using well- known methods such as solvent, emulsion, alkaline, acid, pickling, ultrasonic, or plasma cleaning, each being described by Handbook of Tnbologv Material. Coatings and Surface Treatments. B Bhushan and B K Gupta, 1991

The next step of the process involves contacting the ceramic powder with the shaped metal body in order to form a layer of the ceramic material on the surface(s) of the shaped metal body The ceramic powder can be contacted with the shaped metal body by any means which results in the formation of a layer of the ceramic material on the surface(s) of the shaped metal body, such as thermal spraying (for example, plasma spraying), atomized liquid spraying, dipping, spinning, brushing, rolling, padding, screening (for example, screen printing), soluble gel coating electrostatic spraying, electrophoretic depositing, casting (tape casting) and combinations thereof See, for example, Principles of Ceramic Processing. James Reed, 1988, or Handbook of Tnbologv. Mateπals. Coatings and Surface Treatments. The layer can be a continuous layer or a layer can be deposited in a pattern on a metal body Patterns may be formed by a screen printing or a masking technique Optionally, more than one layer of ceramic material may be used to form the ceramic-metal composite article, or more than one ceramic may be used in a single layer

Preferably, the ceramic powder is blended with a solvent into a slurry mixture in order to improve its ability to be contacted with the surface of the shaped metal body This can be accomplished by any conventional technique, such as wet milling In one embodiment, the ceramic slurry comprises a liquid solvent, a binder, plasticizer, dispersant and the ceramic powder Preferable solvents are water, alcohols and hydrocarbons Preferable binders are wax, resin, gums, polyethylene, latex, acrylics, lanolin, polypropylene, polystyrene, and other thermoplastic polymers Preferable plasticizers are glycols, low molecular weight polymers (for example, liquid at room temperature), oils, fats, and soaps Preferable dispersants are nonionic dispersants such as ethoxylated nonylphenol, anionic dispersants such as magnesium stearate, cationic dispersants such as dodecylaminc hydrochloride, and ampholytic dispersants such as dodecyl betaine After milling the ceramic slurry, it is heated, filtered and de-aired to remove bubbles and agglomerates The ceramic slurry is then contacted with the surface of the shaped metal body

Preferably, the contacting of the ceramic with the shaped metal body is performed by atomized liquid spraying (spraying), tape casting, or screen printing the ceramic material in a layer onto the surface of the shaped metal body See, for example, James Reed, Principles of Ceramic Processing. John Wiley & Sons, New York, 1988 A more preferred method of contacting the ceramic with the shaped metal body involves the use of spraying Spraying typically involves an atomizer with a spray chamber having an inert atmosphere After the ceramic powder slurry previously descπbed is atomized during the spray deposition process, it is evenly deposited on the shaped metal body Spraying involves the

controlled atomization of a slurry and the directed flow of the atomized droplets onto the surface of the shaped metal body On impact with the surface of the shaped metal body, the droplets deform and coalesce into a thick layer The slurry is dried slowly to prevent cracking of the ceramic layer and the drying temperature is controlled below the flash point of the chosen solvent system The time of drying vanes depending upon the solvent used and the thickness of the layer of the ceramic on the shaped metal body It may be necessary to debinder the ceramic material which can be done by any conventional debindeπng technique, for example, by heating under a vacuum or in an inert atmosphere

The thickness of the sprayed Iayer is dependent on the spray geometry, solids content of the slurry, working distance, spraying time or sequence, rebound loss, and film flow Spraying generally results in uniformity of the layering of the ceramic upon the metal The layer thickness generally is any thickness which is sufficient to provide a uniform layer on the surface of the formed metal body such that a complete contacting between the selected ceramic and the selected metal is achieved The layer thickness is dependent on the amount of metal and layer porosity The prefened layer thickness is 1 particle diameter or greater, more preferably 10 particle diameters or greater, and even more preferably 25 particle diameters or greater The preferred layer thickness is 2 mm or less, more prefened 1 mm or less, and even more preferred 0 25 mm or less

Another method of contacting the ceramic powder slurry with a shaped metal body is by tape casting, which allows the formation of a film of controlled thickness of the ceramic material Tape casting provides ceramic substrates with relatively smooth surfaces that are thin, flat and uniform Duπng tape casting, the ceramic powder sluny previously described is tape cast in a layer on the surface of a shaped metal body Tape casting is a process of forming a film of controlled thickness when a slurry flows down an inclined substrate or under a blade onto a supporting surface

If desired, the use of screen printing could also be used to impart some geometry or texturing of the ceramic layer on the surface of the shaped metal body, thus further defining the geometry of the composite body A printing screen is utilized to impart the desired ceramic pattern upon the shaped metal body during screen printing, and the printed image is dried Screen pπntmg processes are further described in greater detail in Kosloff, Screen Printing Techniques. Signs of the Times Publishing Co , Cincinnati, Ohio, 1981

Using the techniques as described for contacting the ceramic powder with the shaped metal body, optional additional layer(s) of ceramic mateπal may be stacked onto the surface of the shaped metal body Additional layers of different types of ceramic material may be optionally layered upon the shaped metal body or different ceramic materials may be layered adjacent to one another, depending on the final use for the ceramic-metal composite article and its desired properties Each of the layering techniques just described can also further define the final shape of the composite body The third step in the process involves infiltrating the ceramic mateπal with the metal of the shaped metal body such that a shaped ceramic-metal composite article is formed Infiltration is the process by which a metal, upon melting, forms a solid-liquid interface with a ceramic, with the metal as

the liquid and the ceramic as the solid, and the metal moves into the pores of the ceramic mateπal by capillary action This process preferably forms a uniformly dispersed and fully dense ceramic-metal composite mateπal Infiltration can be performed by any method that is known in the industry, for example, U S Patents 4,702,770 and 4,834,938 There are many well-known ways of infiltrating a metal into a ceramic body Preferred methods of infiltration are heat infiltration vacuum infiltration, pressure infiltration, and gravity/heat infiltration When the infiltration is performed, the metal wets and permeates the pores of the ceramic that is in contact with the shaped metal body The degree of wetting measured by the contact angle between the metal and the ceramic may be controlled by selecting temperature and time of infiltration The temperature of infiltration is dependent upon the chosen metal for the shaped metal body Infiltration is preferably performed at a temperature such that the metal is molten, but below the temperature at which the metal rapidly evaporates The preferred temperature for infiltration of the selected metal into the selected ceramic depends on the melting temperature of the selected metal For aluminum, the preferred temperature for infiltration of the selected metal into the selected ceramic is 1200°C or less, and more preferably from 1 100°C or less For example, the preferred temperature for infiltration of aluminum into a ceramic is from 750°C or greater, and more preferably 900°C or greater

For each metal, exact temperature and time of infiltration can be established by contact angle measurements to determine when wetting conditions are achieved Infiltration time is dependent on several factors, such as packing density, pore radius, void ratio contact angle, viscosity, surface tension and sample size Infiltration is preferably performed until the metal-infiltrated ceramic mateπal is substantially dense Preferably, the infiltration time for a metal selected from the preferred class of metals and a ceramic selected from the prefened class of ceramics is 0 1 hour or greater, more preferably 0 5 hour or greater, and even more preferably 1 hour or greater Preferably the infiltration time for a metal selected from the preferred class of metals and a ceramic selected from the prefened class of ceramics is 24 hours or less, more preferably 12 hours or less, and even more preferably 6 hours or less For example, the preferred time for infiltration of aluminum into a 1 mm thick layer of boron carbide at 1100°C is 10 minutes Infiltration can be accomplished at atmospheric pressure, subatmospheπc pressures or superatmospheric pressures The infiltration is preferably performed in an inert gas, such as argon or nitrogen At superatmospheric pressure, the infiltration temperature can be lowered Infiltration is preferably performed until the ceramic-metal composite article is densified to greater than 98 percent theoretical density, more preferably to greater than 99 5 percent theoretical density Upon completion of the infiltration step, a fully infiltrated, complex shaped ceramic metal composite article is formed

After infiltration, heat treatment may be optionally performed on the ceramic-metal composite article in order to further tailor mechanical properties of the article A preferred method of alteπng the microstructure of already infiltrated ceramic-metal composites involves post-infiltration heat treatments of the previously infiltrated composites The mechanical properties that can be tailored include fracture

toughness, fracture strength, and hardness This additional step of heating the ceramic metal composite article at a selected temperature for a selected amount of time will decrease the amount of residual free metal and improve the uniformity of the multi-phase ceramic-based material As a result of the post- lnfiltration heat treatment, a slow growth of ceramic phases takes place It is during this heat treatment that the greatest control over the formation of multi-phases and the above-stated mechanical properties in the ceramic-metal composite article is achieved The temperature at which the heat treatment is performed is a temperature at which the residual free metal will decrease Furthermore, the temperature at which the heat treatment is performed is the lowest temperature at which chemical reactions in the solid state are taking place A preferred method of altering the microstructure of already infiltrated ceramic-metal composites involves post-heat treatments of already infiltrated composites at 650°C or greater, more preferably 700°C or greater The maximum temperature for post-heat treatment is the melting point of the metal m the ceramic-metal composite article The time of heat treatment is preferably long enough that the desired properties in the ceramic metal composite article are achieved by altering the microstructure For example, in the case of aluminum-boron-carbide, this additional step of heat treating is preferably accomplished by heating the infiltrated body to a temperature of 660°C or greater, more preferably 700°C or greater, and even more preferably 800°C or greater Preferably, the heat treatment is accomplished at a temperature of 1500°C or less, more preferably at 1200°C or less, and even more preferably 1000°C or less The preferable time period for the heat treatment of aluminum-boron-carbide is from 1 hour or greater, more preferably 25 hours or greater The heat treatment may be performed in air or an inert atmosphere such as nitrogen or argon Preferably, the heat treatment is performed in air

After infiltration and optional heat treatment, the infiltrated body is cooled Optionally, the infiltrated metal may be machined and polished into a final desired shape It may be desirable to polish the infiltrated article depending upon the end usage for the infiltrated article For example, if the desired article is a computer hard disk, the surface of the disk should be polished to a substantially uniform average roughness value of between 1 and 2000 A ( 1 x 10 '°m and 2 10 ⁷ m) Also for example, if the desired article is a computer disk, a coating may be applied to the disk in order to impart texture to the surface of the composite article A suitable coating, for example, is a nickel-phosphorus coating, however, other types of coatings can be used such as, for example, metals and polymers If a nickel- phosphorus coating is used on an article such as a computer hard disk, the current industry procedures for manufacturing and utilizing disks may be used The coating method may be any that provides dense coating, such as atomic deposition, particulate deposition, bulk coating, or surface modification The most typical method of coating is electroplating The coating itself may be further treated to provide a textured surface, either over the entire surface or a portion of the surface The further treatment may be accomplished by techniques such as mechanical techniques, chemical or optical techniques, electrical techniques, or a combination thereof

The process for preparing the complex-shaped ceramic-metal composite articles allows the creation of solid yet complex-shaped ceramic-metal composite articles with little or no shnnkage of the article once the shaped metal body is formed, so any article where net shape is desirable through forming of the shaped metal initially may be formed through this process Prefened products of this invention are computer hard disks and hard disk dπve components, wherein the material has a high hardness, a high wear resistance, a high fracture toughness, a high damping capability, a low density, and a high specific stiffness and is electrically conductive There are also many other applications for thin, complex-shaped ceramic metal composite articles such as porous filters, thin journal bearings, small thin spindles, bearing races, combustion cylinder liners, piston rings, decorative jewelry, satellite mirrors and other high precision mirrors, cutting implements, elements of electπc contacts and electric switches

The following are included for illustrative purposes only and are not intended to limit the scope of the claims. Example 1

The paint on an aluminum beverage can was removed by sand-blasting A fine boron-carbide powder having an average particle size of 3 microns (3 x 10 ' mm)was dispersed by ultrasonic agitation in methanol, creating a slurry containing 25 volume percent of said powder in methanol The boron- carbide powder was deposited on the can by spraying the slurry onto the outer surfaces of the can and treating the can at 45°C for 26 hours in air After said treatment, the can had a dπed coating of boron- carbide powder on the surface of the can The boron-carbide powder coating the can was infiltrated by the aluminum of the can by heating the can coated with boron-carbide in a graphite vacuum furnace to 1150°C for 15 minutes at a heating rate of 10°C/mιnute and under a vacuum of less than 1 Torr ( 133 Pa) The can was cooled by shutting off the power to the furnace The resultant infiltrated boron-carbide- alummum composite essentially retained the original shape of the aluminum can