Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/02—Making non-ferrous alloys by melting
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/05—Mixtures of metal powder with non-metallic powder
  • C22C1/058—Mixtures of metal powder with non-metallic powder by reaction sintering (i.e. gasless reaction starting from a mixture of solid metal compounds)
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/10—Alloys containing non-metals
  • C22C1/1036—Alloys containing non-metals starting from a melt
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/10—Alloys containing non-metals
  • C22C1/1036—Alloys containing non-metals starting from a melt
  • C22C1/1047—Alloys containing non-metals starting from a melt by mixing and casting liquid metal matrix composites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps

Definitions

• the present invention relates to composite materials comprising a metal l i c matrix havi ng second phase parti cl es di spersed therei n .
• the metallic matrix may comprise a metal, metal alloy or intermetallic.
• the second phase may comprise at least one ceramic, such as a boride, carbide, nitride, silicide, oxide or sulfide, or may comprise an intermetallic of different composition than the matrix.
• the process for formation of the metal-second phase composites of the present invention involves the use of arc-melting techniques for introducing the second phase particles into the final metallic matrix desired.
• Arc-melting techniques have conventionally been applied to the production of refractory metals, such as titanium and titanium alloys.
• refractory metals such as titanium and titanium alloys.
• titani um i ngot, titani um sponge, and optional ly titanium revert is crushed and compressed into electrode compacts which are welded together to form a long consumable electrode for vacuum arc melting.
• Arc melting under vacuum is necessary since it prevents the molten titanium from reacting with oxygen and nitrogen in the air.
• the consumabl e electrode becomes the anode in a vacuum arc furnace and a water-cooled copper crucible serves as the cathode. An arc is struck between the compacted electrode and the copper crucible to melt the compact.
• the molten metal collects and solidifies in the copper crucible.
• alloying materials are uniformly mixed with the crushed titanium sponge before compacting.
• Double melting is used to insure homogeneity of the ingots.
• the ingot from the first melting serves as the electrode for the second melting.
• Triple melting is also used in certain instances to achieve better uniformity and to reduce oxygen or nitrogen rich inclusions in the microstructure by providing an additional melting step to dissolve them.
• arc-melting procedures have been used to produce titanium aluminide intermetallic materials, such as TiA1 and Ti 3 Al.
• the process is similar to that used for titanium alloy ingots and involves forming a compacted electrode of titanium sponge and aluminum in the proper proportions to form the desired titanium aluminide composition.
• Arc-melting techniques have been used to produce titanium, titanium alloy and titanium aluminide ingots weighing up to 10 tons and having diameters of up to 40 inches.
• the powder metal l urgi cal type production of such dispersion- strengthened-composites would ideally be accomplished by mechanically mixing metal powders of approximately 5 micron diameter or less with the appropriate oxide or carbide powder (preferably 0.01 micron to 0.1 micron). High speed blending techniques or conventional procedures such as ball milling may be used to mix the powder. Standard powder metallurgy consolidation techniques are then employed to form the final composite.
• the ceramic component is large, i.e., greater than 1 micron, due to a lack of availability, and high cost, of very small particle size materials since their production is energy intensive, time consuming, and costly in capital equipment.
• the production, mixing and consolidation of very small particles inevitably leads to contamination at the surface of the particles.
• Contaminants such as oxides, inhibit interfacial binding between the ceramic phase and the matrix, thus adversely effecting ductility of the composite.
• Such weakened i nterfacial contact can also result in reduced strength, loss of elongation, and facilitated crack propagation.
• the matrix may be adversely effected, as in the case of titanium which is embrittled by interstitial oxygen.
• composites produced by conventional powder metallurgy techniques are typically not suitable for remelting, due to the tendency for the dispersoid particles to segregate within the molten matrix metal, causing particle agglomeration upon solidification.
• the particulate materials are available in the desired size, they are extremely hazardous due to their pyrophoric nature.
• molten metal infiltration of a continuous ceramic skeleton has been used to produce composites.
• elaborate particle coating techniques have been developed to protect the ceramic particles from the molten metal during admixture or molten metal infiltration, and to improve bonding between the metal and ceramic.
• Techniques such as these have resulted in the formation of silicon carbide-al umi num composites, frequently referred to as SiC/A1, or SiC aluminum. This approach is only suitable for large particulate cerami cs (e.g., greater than 1 micron) and whiskers, because of the high pressures involved for infiltration.
• the ceramic material such as silicon carbide
• liquid metal is forced into the packed bed to fill the intersticies.
• U.S. Patent 4,444,603 of Yamatsuta et al, issued April 24, 1984. Because of the necessity for coating techniques and molten metal handling equipment capable of generating extremely high pressures, molten metal infiltration has not been a practical process for making metal-ceramic composites.
• dispersion strengthened metals such as internally oxidized aluminum in copper.
• a metal containing a more reactive component When a copper alloy containing about 3 percent aluminum is placed in an oxidizing atmosphere, oxygen may diffuse through the copper matrix to react with the aluminum, precipitating alumina.
• This technique although limited to relatively few systems since the two metals utilized must have a wide difference in chemical reactivity, has offered a feasible method for dispersion hardening.
• the highest possible level of dispersoids formed in the resultant dispersion strengthened metal is generally insufficient to impart significant changes in properties such as modulus, hardness, and the like.
• oxides are typically not wetted by the metal matrix, so that interfacial bonding is not optimum.
• Spray forming techniques which have conventionally been used to produce superalloy near net-shape products, have recently been applied to the formation of metal-ceramic composites.
• a particular spray forming process known as the Osprey process involves providing a source of molten alloy, converting the alloy into a spray of molten droplets by means of gas atomization, directing the droplets towards a collecting surface and then recoalesing the droplets at the collector to form a near net-shape product.
• Metal-ceramic composite articles may be produced by injecting ceramic particles into the atomizing zone during the deposition operation. Ceramic particles in the size range of 5 microns and larger have been used to produce composites containing up to 25 volume percent ceramic.
• the SHS process involves mixing and compacting powders of the constituent elements, and igniting the green compact with a suitable heat source. On ignition, sufficient heat is released to support a self-sustaining reaction, which permits the use of sudden, low power initiation of high temperatures, rather than bulk heating over long times at lower temperatures.
• a suitable heat source On ignition, sufficient heat is released to support a self-sustaining reaction, which permits the use of sudden, low power initiation of high temperatures, rather than bulk heating over long times at lower temperatures.
• Exemplary of these techniques are the patents of Merzhanov et al .
• U.S . Patent 3, 726, 643 there is taught a method for producing high-melting refractory inorganic compounds by mixing at least one metal selected from groups IV, V, and VI of the Periodic System with a non-metal such as carbon, boron, silicon, sulfur, or liquid nitrogen, and locally heating the surface of the mixture to produce a local temperature adequate to initiate a combustion process.
• U.S. Patent 4,161,512 a process is taught for preparing titanium carbide by localized ignition of a mixture consisting of 80-88 percent titanium and 20-12 percent carbon, resulting in an exothermic reaction of the mixture under conditions of layer-by-layer combustion.
• These references deal with the preparation of ceramic materials, in the absence of a second non-reactive metallic phase.
• U.S. Patent 4,431,448 teaches preparation of a hard alloy by intermixing powders of titanium, boron, carbon, and a Group I-B binder metal, such as copper or silver, compression of the mixture, local ignition thereof to initiate the exothermic reaction of titanium with boron and carbon, and propagation of the reaction, resulting in an alloy comprising titanium diboride, titanium carbide, and the binder metal.
• This reference is limited to the use of Group I-B metals such as copper and silver, as binders.
• the process is performed with a relatively high volume fraction of ceramic and a relatively low volume fraction of metal (typically 6 volume percent and below, and almost invariably below 20 volume percent).
• the product is a dense, sintered material wherein the relatively ductile metal phase acts as a binder or consolidation aid which, due to applied pressure, fills voids, etc., thereby increasing density.
• the intermediate material may be introduced into the host metal by addition to a molten bath of the host metal, or by admixing with solid host metal, followed by heating to a temperature sufficient to melt the host metal.
• the process of the present invention is a modification of the latter process, in that arc-melting techniques are used to heat a solid mixture of intermediate material and host metal to form the desired final metallic matrix-second phase composites.
• U.S. Patent Application Serial No. 873,890 filed June 13, 1986, which is hereby incorporated by reference, is specifically drawn to the production of metallic-second phase composites in which the metallic matrix comprises an intermetallic material, such as an aluminide.
• a first composite is formed which comprises a dispersion of second phase particles within a metal or metal alloy matrix. This composite is then introduced into an additional metal which is reactive with the matrix metal to form an intermetallic matrix.
• One method for introducing the first composite into the intermetallic forming metal involves placing both the first composite and the intermetallic precursor metal together in solid form in a vessel, followed by heating to a temperature at which the intermetallic precursor metal melts.
• Certain embodiments of the present invention which involve the formation of composites having intermetallic matrices, constitute an improvement of this previously disclosed process.
• the arc-melting methods of the present invention may advantageously be used to heat a solid mixture consisting of a first composite comprising second phase particles in a metal or metal alloy matrix, and an intermetallic precursor metal which is reactive with the metal matrix of the first composite to form an inter metallic.
• a final intermetallic-second phase composite is thereby produced by the arc-melting method of the present invention.
• U.S. Patent No. 4,738,389 to Moshier et al which is hereby incorporated by reference, relates to a method for welding which utilizes metal-ceramic composites as weld filler material.
• a pre-formed weld rod of metal-ceramic composite is produced which may be used in conventional welding operations such as arc, resistance, gas, laser, and electron beam type welding processes.
• reactive ceramic-forming constituents and a solvent metal are formed into a suitable shape which may be used for welding.
• a ceramic-forming reaction occurs during the welding process to produce the desired metal-ceramic composite filler material.
• the ceramic-forming constituents and solvent metal may, for example, be in the form of a rod of compacted powders or in the form of twisted wires comprising the individual ceramic-forming constituents and solvent metal. Again, conventional welding operations are used in this embodiment to produce the metal-ceramic weldment.
• the metallic matrix may comprise a metal, metal alloy or intermetallic, while the particulate second phase may constitute a ceramic, such as a boride, carbide, nitride, silicide, oxide or sulfide, or may constitute an intermetallic compound other than the matrix material.
• the method involves forming an intermediate composite material comprising second phase particles dispersed throughout a solvent metal matrix, mixing the intermediate composite with a solid host metal, and arc-melting the mixture to melt the solvent metal matrix and the host metal to thereby form a dispersion of second phase particles within a final metallic matrix.
• the process of the present invention involves the formation of a typically porous, friable intermediate composite material which is then introduced into a host metal by arc-melting techniques to form a dense final composite product.
• the intermediate composite material is formed by reacting second phase-forming constituents in the presence of a solvent metal to form a finely-divided dispersion of second phase particles within a matrix of the solvent metal.
• This intermediate material is then introduced into a host metal, which may be the same as, or different from, the solvent metal, to form a final composite comprising a lower loading of the second phase particles within a final metallic matrix.
• the method of introducing the intermediate material into the host metal preferably utilizes an arc-melting technique which involves mixing the intermediate material and host metal together in solid form and then melting the consolidated mixture in an arc-melting furnace to form a dense final composite material.
• arc-melting techniques constitute the preferred method of the present invention
• additional techniques such as plasma arc-melting, laser melting, and electron beam melting may also be used .
• the final composite material produced comprises discrete second phase particles dispersed throughout a final metal, metal alloy or intermetallic matrix.
• the present invention encompasses features which are directly contrary to the prior art wisdom in materials science, and particularly in the field of metal-second phase composites. For instance, the present process utilizes intermediate materials of typically low strength, high porosity, high friability, etc. Further, the process involves the use of molten metals to convert these intermediate materials of low mechanical quality to high quality, dense final composite materials.
• the composite is produced via solid powder metallurgical techniques, as opposed to liquid metal techniques (ingot metallurgy), because the thoria ceramic tends to segregate, and even rise to the surface of the melt, due to surface tension effects.
• welding is again a problem because of the presence of liquid metal, this time giving rise to the above-noted segregation.
• the arc-melting method of the present invention advantageously makes use of molten metal to form final metallic matrix-second phase composites. This is particularly surprising because arc-melting techniques constitute a relatively violent method for melting metals, in that extremely high temperatures which are well above the melting point of the final metallic matrix may be reached.
• elements which are suitable for use as second phase-forming constituents include those elements which are reactive to form ceramics or intermetallics, such as aluminum, titanium, zirconium, hafnium, vanadium, niobium, tantalum, beryllium, manganese, chromium, molybdenum, tungsten, iron, cobalt, nickel, copper, silicon, boron, carbon, sulfur, nitrogen, oxygen, thorium, scandium, lanthanum, yttrium, cerium and erbium.
• the second phase-forming constituents may be provided in elemental form, or may be provided as an alloy of the solvent metal.
• reactive compounds of such elements such as boron nitride (BN), boron carbide (B 4 C), boron oxide B 2 O 3 ), aluminum boride (AlB 12 ), aluminum carbide (A1 4 C 3 ), aluminum nitride (A1N), silicon carbide (SiC), copper oxide (CuO) and iron oxide (Fe 2 O 3 ) may also be used as a source of second phase-forming constituents.
• suitable second phase particles are ceramics, such as borides, carbides, nitrides, oxides, suicides and sulfides of metals of the fourth to sixth groups of the Periodic Table.
• Ceramic second phase particles include TiB 2 , ZrB 2 , HfB 2 , VB 2 , NbB 2 , TaB 2 , MoB 2 , TiC, ZrC, HfC, VC, NbC, TaC, WC, TiN, Ti 5 Si 3 , Nb 5 Si 3 , ZrSi 2 , MoSi 2 and
• Complex compounds are also suitable as second phase particles.
• the particles may comprise borides, carbides, or nitrides of at least two transition metals of the fourth to sixth groups of the Periodic Table, such as titanium niobium boride ([Ti,Nb] ⁇ B y ) or titanium vanadium carbide ([Ti,V] ⁇ C y ).
• Complex compounds containing one of the constituents of the final metallic matrix are often found to be very stable.
• second phase particles of [Ti,Nb] ⁇ B y are highly stable in both TiAl and Nb 3 Al intermetallic final matrices. It has also been found that complex compounds, in some instances, tend to form whisker shaped particles, which may be beneficial in providing enhanced mechanical properties, such as creep resistance, in the final composites formed.
• plural second phase dispersoids may advantageously be dispersed in the final metallic matrix. This may be achieved by forming an intermediate material containing plural second phase materials within the solvent metal matrix. For example, titanium, boron and nitrogen second phase-forming constituents may be reacted in the presence of a solvent metal, such as aluminum, to form an intermediate material comprising a dispersion of TiB 2 and TiN particles within a matrix of the solvent metal.
• plural second phase particulate materials may be dispersed in the final metallic matrix by using multiple intermediate materials. For example, an intermediate material comprising TiB 2 particles in an aluminum matrix may be combined with another intermediate material comprising TiN particles in an aluminum matrix. This combination may then be mixed with titanium host metal and melted in an arc-melting furnace to form a dispersion of TiB 2 and TiN second phase particles within a titanium aluminide final matrix.
• the size of the second phase particles may range from about 0.01 to about 10 microns, and more preferably may range from about 0.01 to about 5 microns. It is possible, however, to produce second phase particles of larger size, depending upon the desired use of the final composites formed.
• the whiskers may range in diameter from about 1 to about 5 microns and in length from about 5 to about 200 microns. More preferably, the whiskers may range in diameter from about 1 to about 3 microns and in length from about 5 to about 50 microns. The length to diameter, or aspect ratio of the whiskers may range from about 10:1 to about 100:1.
• second phase particle loadings are possible in the final composites of the present invention.
• the percentage of second phase particles may be varied considerably, depending upon the intended use of the final composite material.
• second phase particle loadings of from about 1 to about 40 volume percent may be utilized.
• second phase loadings of from about 1 to about 10 volume percent may be used.
• the intermediate materials may be comprised of from about 20 to about 80 volume percent second phase particles, while the final composites may be comprised of from about 1 to about 40 volume percent second phase.
• the solvent metal one may use at least one metal or metal alloy capable of dissolving or at least sparingly dissolving at least one of the second phase-forming constituents and having a lesser capability for dissolving or otherwise reacting with the formed second phase particles.
• the solvent metal may act as a solvent for the second phase-forming constituents, but not for the desired second phase particles.
• the host metal one may use an additional amount of the solvent metal, or one may use a metal, metal alloy or intermetallic which forms an alloy or intermetallic with the solvent metal.
• the intermediate material in which the intermediate material is introduced into the host metal, temperatures above the melting point of the solvent and host metals are typically reached. Therefore, care must be taken in chosing a solvent metal/host metal combination which, when in the molten state, remains substantially inert with respect to the second phase particles. Also, it is important to prevent an undesireable amount of second phase particle dissolution or growth during the arc-melting process. The second phase particles must therefore remain stable in a melt of the solvent and host metals for an amount of time sufficient to complete the arc-melting process. While the potential choice of solvent and host metals is large, this choice is limited by adherence to the criteria noted above.
• Suitable solvent and host metals include aluminum, nickel, copper, titanium, cobalt, iron, platinum, gold, silver, niobium, tantalum, boron, zinc, molybdenum, yttrium, hafnium, tin, tungsten, lithium, magnesium, beryllium, thorium, silicon, chromium, vanadium, zirconium, manganese, scandium, lanthanum, cerium, erbium and alloys or intermetallics of such metals.
• Preferred solvent metals include aluminum, nickel, titanium, cobalt, iron, copper, niobium, chromium, silicon, magnesium and beryllium.
• the host metal may comprise material other than conventional metals, metal alloys or intermetallics.
• the host metal may, for example, be a dispersion strengthened metal such as metal containing finely dispersed erbium oxide, thoria, alumina, etc. It is important in these cases that the preexisting dispersion be stable in the molten metal for the time/temperature required for the arc-melting process.
• a metallic-second phase composite prepared in accordance with the present invention, as the host metal .
• the advantage of utilizing a material containing a second phase dispersion as the host is that a bimodal distribution of second phase types, shapes, amounts, etc. may be obtained.
• a host metal comprising an aluminum matrix containing a dispersion of essentially equiaxed TiB 2 particles, into which an intermediate material containing TiN needle shaped particles is added.
• a combination of dispersion strengthening and high temperature creep resistance may be achieved.
• the term "host metal” encompasses the types of materials discussed above containing preexisting second phase dispersions.
• the final metallic matrix of the present invention may be comprised of a wide variety of metal, metal alloy and intermetallic materials.
• Suitable final matrix metals include aluminum, nickel, copper, titanium, cobalt, iron, platinum, gold, silver, niobium, tantalum, boron, zinc, molybdenum, yttrium, hafnium, tin, tungsten, lithium, magnesium, beryllium, thorium, silicon, chromium, vanadium, zirconium, manganese, scandium, lanthanum, cerium, erbium and alloys or intermetallics of such metals.
• intermetallic materials are the aluminides and suicides.
• metallic elements capable of forming aluminides are titanium, nickel, iron, cobalt, and refractory metals such as niobium, zirconium, molybdenum, vanadium, tantalum and the like.
• metallic elements capable of forming silicides are titanium, niobium, chromium, cobalt, vanadium, nickel, and molybdenum.
• Specific final intermetallic matrix materials include Ti 3 Al, TiAl, TiAl 3 , Ni 3 Al, NiAl, Nb 3 Al, Nb 2 Al , NbAl 3 , Co 3 Al, ZrAl 3 , ZrAl 2 , Zr 2 Al 3 , Zr 4 Al 3 , Zr 3 Al 2 , Zr 3 Al, Fe 3 Al, Ta 2 Al, TaAl 3 , Mo 3 Al , MoAl 2 , VAl 3 , VAl, Ti 5 Si 3 , Nb5Si3, Cr 3 Si, Cr 2 Si, V 5 Si 3 , Ni 3 Si, CoSi 2 and Cr 2 Nb.
• Plural intermetallic materials may be present in the final matrix.
• a final matrix may be comprised of a two phase mixture of TiAl and Ti 3 Al, or alternatively of a two phase mixture of TiAl 3 and TiAl.
• the final metallic matrices of the present invention exhibit relatively fine grain size.
• the average grain size of the final matrices may range from about 0.1 micron to about 200 microns, and more preferably may range from about 1 micron to about 40 microns.
• an arc-melted ingot comprising a final matrix of TiAl (gamma) intermetallic reinforced with 5 volume percent TiB 2 second phase particles may exhibit an average colony size of approximately 30 microns.
• various techniques may be used to produce the intermediate material or sponge. Each of these methods involves the preparation of a mixture of the second phase-forming constituents, along with at least one solvent metal which acts to form the solvent metal matrix. The mixture is then reacted by the techniques described below to form a dispersion of second phase particles within the solvent metal matrix.
• the second phase-forming constituents may be provided in the form of elemental powders, or at least one of the constituents may be provided in the form of an alloy of the solvent metal.
• at least one of the second phase-forming constituents may be provided from a reactive compound.
• the second phase-forming reaction is initiated by bulk heating a mixture comprising the second phaseforming constituents and at least one solvent metal.
• the starting mixture is preferably compressed to form a compact which is then heated in, for example, a furnace to initiate the second phase-forming reaction.
• the reaction typically occurs at a temperature approximating the melting tempera ture of the solvent metal.
• Bulk heating may also be achieved by plasma spray techniques in which the starting mixture is introduced into a plasma flame.
• the starting mixture may be in the form of elemental or mechanically alloyed powders.
• intermediate materials comprising second phase particles dispersed in a solvent metal matrix are formed using a local ignition process.
• a mixture comprising the second phase-forming constituents and at least one solvent metal is compressed to form a green compact, followed by local ignition to initiate a reaction wave front which moves along the compact.
• the propagating reaction results in the in-situ precipitation of substantially insoluble second phase particles in the solvent metal matrix.
• the degree of porosity of the intermediate material can be varied by procedures such as vacuum degassing or compression applied prior to, during, or subsequent to initiation of the second phase-forming reaction. Porosity of the intermediate material may be minimized by a vacuum degassing operation prior to initiation of the reaction, if so desired.
• the degree of vacuum applied and temperature of the degassing step is determined purely by the kinetics of evaporation and diffusion of any absorbed moisture or other gases. High vacuum and elevated temperatures aid the degassing operation. Absent the degassing step, the intermediate material formed may be relatively porous and low in density.
• porosity is, in most cases, preferred, since it is conducive to more rapid dissolution of the solvent metal matrix in the host metal during subsequent arc-melting processing.
• the porosity of the intermediate materials produced by the bulk heating and local ignition embodiments is typically relatively high. For example, porosity in most cases exceeds about 10 percent, and may often exceed about 25 percent.
• a porosity enhancer such as a low boiling point metal, e.g., magnesium or zinc, in the initial reaction mixture. The enhancer volatilizes during the second phase-forming reaction, thereby increasing porosity of the resultant intermediate material.
• Another alternative embodiment for the formation of intermediate materials involves a direct addition process .
• a mixture comprising the second phase-forming constituents and at least one solvent metal is added to a molten bath of metal, resulting in the in-situ formation of second phase particles within a metal matrix.
• the mixture may be added to the molten metal in the form of a preform or compact.
• a solvent metal must be present in the preform or compact to facilitate the reaction of the second phase-forming constituents.
• intermediate materials formed by the methods above are then introduced into a host metal, which may be the same as, or different from, the solvent metal matrix of the intermediate material.
• the method of introducing the intermediate material into the host metal utilizes an arc-melting technique which involves mixing and mechanically consolidating the intermediate material and host metal together in solid form to form a compacted electrode, and then melting the consolidated mixture in a conventional arc-melting furnace to form a dense ingot of final composite material. Alloying additions may also be incorporated into the compacted electrode mixture at this time. Mixing of the intermediate material with the host metal is facilitated by crushing the intermediate material to a suitable size. This is easily achieved since the intermediate material is typically in the form of a friable, porous sponge.
• the host metal may be provided in any form that is convenient for mixture and consolidation with the intermediate material.
• a titanium host metal may be provided in the form of crushed titanium sponge.
• An aluminum host metal for example, may be provided in the form of 1 centimeter diameter shot.
• Compacts of the intermediate material-host metal mixture may optionally be welded together to form a long electrode for arc-melting.
• the compacted electrode is then melted by conventional arc-melting techniques in an electric arc furnace.
• the electrode acts as the anode and a water-cooled copper crucible serves as the cathode in the arc-melting procedure.
• the intermediate material may be crushed to a fine powder, mixed with a fine powder of host metal, and compacted into a rod which is then melted using the welding techniques of the 4,738,389 Patent.
• the intermediate material may be formed into a wire which is then twisted with a wire of the host metal and then melted using the previously disclosed welding techniques.
• such compacted rods or twisted wires comprising the intermediate material and host metal may be melted by techniques other than welding processes.
• conventional plasma spray processing may be used in which the rod or wire is introduced into the stream of a plasma spray gun to effect melting, and to produce the desired final composite.
• the final compositions of the arc-melting process comprise a dispersion of second phase particles throughout a final metallic matrix.
• Ingots of relatively large size i.e., on the order of several thousand pounds, may be produced in one arc-melting run. Therefore, the arc-melting process of the present invention allows for the production of large, industrial quantities of metallic-second phase composite materials.
• the methods of the present invention may be utilized to form other cast products.
• Conventional investment casting, squeeze casting, rheocasting and spray casting procedures may be used during the arc-melting process of the present invention to produce various product forms.
• a melt comprising a molten final composite which is formed during the arc-melting procedure may be subjected to a variety of casting procedures to yield a wide range of final composite product forms.
• a molten melt formed by the arc-melting step of the present invention may be subjected to conventional Osprey processing techniques to produce a spray-formed shape comprising the desired final metallic-second phase composite.
• Osprey processing techniques to produce a spray-formed shape comprising the desired final metallic-second phase composite.
• examples 1 through 23 illustrate the production of intermediate materials which are suitable for introduction into host metals.
• examples 24 through 36 illustrate the formation of compacted electrodes of intermediate material and host metal , and the arc-melting of the electrodes to form ingots of final composite materials.
• a mixture of powders comprising 34 percent by weight titanium, 16 percent by weight boron and 50 percent by weight aluminum, is isostatically compacted to 38,000 pounds per square inch.
• the compacted artifact is then heated in a furnace set at a temperature of 800oC.
• a rapid increase in temperature to approximately 1250oC is noted.
• the rate of increase in temperature is very rapid (greater than 900oC per minute) followed by a fast cool down rate of approximately 400oC per minute.
• the intermediate material formed is found to contain a fine dispersion (0.1 - 3 microns) of substantially unagglomerated titanium diboride second phase particles in an aluminum solvent metal matrix.
• Titanium, boron, and aluminum powders are ball-milied in the proper stoichiometric proportions to provide 60 weight percent titanium diboride second phase in an aluminum solvent metal matrix.
• the mixture is then packed in gooch tubing and isostatically pressed to 40 ksi, forming a compact approximately 1 centimeter in diameter by 5 centimeters long and having a density of 2.39 grams per cubic centimeter.
• the compact is then placed end to end with a graphite rod in a quartz tube under flowing argon at atmospheric pressure.
• the graphite rod is heated in a radio frequency field which initiates a reaction at the interface of the compact and the rod.
• the reaction propagates the length of the compact at a rate of 0.77 centimeters per second.
• Analysis of the resultant intermediate material reveals a dispersion of substantially unagglomerated titanium diboride second phase particles having an average size of approximately 1 micron in an aluminum solvent metal matrix.
• Niobium, boron, and aluminum powders are mixed in the proper stoichiometric proportions to provide 50 weight percent niobium diboride second phase in an aluminum solvent metal matrix.
• the mixture is packed in gooch tubing and isostatically pressed to 40 ksi, forming a compact.
• the compact is then placed in a quartz tube under flowing argon at atmospheric pressure and heated in a radio frequency field to initiate a reaction of the compact.
• An intermediate material is thereby formed comprising substantially unagglomerated niobium diboride second phase particles ranging in size from about 1 to about 7 microns dispersed in an aluminum solvent metal matrix.
• a mixture of 20.5 weight percent titanium, 9.5 weight percent boron and 70 weight percent cobalt is isostatically pressed to 40 ksi and heated in a furnace.
• a highly exothermic reaction occurs at 800oC, with a temperature rise to about 1500oC.
• Subsequent X-ray analysis of the resultant intermediate material identifies the presence of titanium diboride second phase particles in a cobalt solvent metal matrix. It is shown here that if sufficient diffusion of the second phase-forming constituents into the solid solvent metal can occur, the initiation temperature of the second phase-forming reaction can be below the melting point of the solvent metal, which in this case is 1495oC, and the reaction may be initiated in the solid state.
• a mixture of 20.6 weight percent titanium, 9.4 weight percent boron and 70 weight percent chromium is compacted to 40 ksi and then heated in a furnace. A rapid exothermic reaction is noted at approximately 880o C.
• the resultant intermediate material comprises titanium diboride second phase particles in a chromium solvent metal matrix.
• a mixture of 16 weight percent aluminum, 56 weight percent chromium, 20.6 weight percent titanium, and 9.4 weight percent boron is compacted and subsequently heated in a furnace.
• a temperature of about 620o C On attainment of a temperature of about 620o C, a rapid reaction occurs, resulting in a temperature increase to over 800o C and melting of the chromium.
• the temperature-time curve shows a double peak, indicating an exothermic reaction in aluminum (which typically occurs between 600o-680oC) and a subsequent reaction in the chromium.
• the lower melting aluminum solvent metal therefore acts as a "low temperature initiator" for the reaction, which releases heat and induces further reaction in the higher melting chromium solvent metal.
• the intermediate material produced comprises titanium diboride second phase particles in a solvent metal matrix of chromium-aluminum alloy.
• a mixture of approximately 40 weight percent zirconium, 20 weight percent boron and 40 weight percent copper powders is compacted and then heated in a furnace until a rapid exothermic reaction occurs.
• X-ray and SEM analyses of the resultant intermediate material show the presence of zirconium diboride second phase particles in a copper solvent matrix.
• the following example illustrates the formation of an intermediate material comprising titanium vanadium carbide ([Ti,V] x C y ) second phase particles of elongated shape dispersed within an aluminum solvent metal matrix.
• 37 grams of Ti powder (-100 mesh), 13 grams of V powder (-325 mesh), 10 grams of C powder (-325 mesh) and 40 grams of Al powder (-325 mesh) are ball milled and isostatically pressed to 40 ksi to form a compact.
• the compact is heated in a radio frequency field to initiate an exothermic reaction.
• SEM analysis of the resultant material reveals titanium vanadium carbide second phase particles of elongated shape having widths of approximately 3 to 5 mircons and lengths of approximately 10 to 80 microns dispersed in a solvent metal matrix of Al.
• the following example illustrates the formation of an intermediate material comprising titanium zirconium carbide ([Ti,Zr] x C y ) second phase particles of elongated shape dispersed within an aluminum solvent metal matrix.
• Powders of Al 4 C 3 , Zr, Ti and Al are ball milled and isostatically pressed to 40 ksi to form a compact.
• the compact is heated in a radio frequency field to initiate an exothermic reaction.
• SEM analysis of the resultant intermediate material reveals titanium zirconium carbide second phase particles of elongated shape having widths of approximately 2 to 4 mircons and lengths of approximately 10 to 40 microns dispersed in a solvent metal matrix comprising Al.
• Ti, Nb, B and Al powders (-325 mesh) are blended, packed in gooch tubing and isostatically pressed to 40 ksi to form a compact.
• the compact is placed on a water cooled cold finger in a quartz tube under flowing argon and is heated in a radio frequency field to initiate a reaction of the compact.
• Analysis of the resultant intermediate material reveals a dispersion of titanium niobium boride ([Ti,Nb] x B y ) whiskers within an aluminum solvent metal matrix.
• the aspect ratio of the wiskers is greater than 20:1.
• a mixture of BN, Ti and Al powders is compacted and heated to ignition at about 730oC, marked by a sudden temperature rise.
• X-ray and SEM analyses of the resultant intermediate material confirm the presence of TiB 2 and TiN second phase particles dispersed in an Al solvent metal matrix with a particle loading of about 50 weight percent.
• the size of the TiB 2 and TiN second phase particles ranges from about 1 to 10 microns.
• Example 13 A similar experiment to the one described in Example 13 is performed except that copper is used as the solvent metal. Ignition in copper occurs at about 900oC. X-ray and SEM analyses confirm the presence of TiB 2 and TiN second phase particles dispersed in a Cu solvent metal matrix with a particle loading of about 50 weight percent. The size of the TiB 2 and TiN second phase particles is less than about 1 micron.
• Ti and Cu powders are mixed, compacted to 40 ksi and heated in a radio frequency field.
• a second phase-forming reaction is initiated at a temperature of about 850oC.
• Subsequent analysis of the resultant intermediate material reveals a dispersion of TiB 2 and TiC second phase particles in a Cu solvent metal matrix with a particle loading of about 30 weight percent.
• Powders of AlN, Ti and Al in the proper stoichiometric proportions to produce an intermediate material comprising 60 weight percent TiN second phase particles in an aluminum solvent metal matrix are ball milled and then compacted to 40 ksi.
• the compact is placed on a water cooled copper boat in a quartz tube under flowing argon and inductively heated to initiate an exothermic reaction.
• the resultant intermediate material comprises TiN second phase particles of a generally rod-like shape having widths of approximately 1 to 2 microns and lengths of 5 to 10 microns dispersed in an aluminum solvent metal matrix.
• Powders of Ti, Si and Al in the proper stoichiometric proportions to produce an intermediate material comprising 50 weight percent Ti 5 Si 3 second phase particles in an aluminum solvent metal matrix are mixed and then compacted to 40 ksi.
• the compact is placed on a water cooled copper boat in a quartz tube under flowing argon and inductively heated to initiate an exothermic reaction.
• the resultant intermediate material comprises Ti 5 Si 3 second phase particles dispersed in an aluminum solvent metal matrix.
• Ti, V, B and Al powders (-325 mesh) are blended, packed in gooch tubing and isostatically pressed to 40 ksi to form a compact.
• the compact is placed on a water cooled cold finger in a quartz tube under flowing argon and is heated in a radio frequency field to initiate a reaction of the compact.
• Analysis of the resultant intermediate material reveals a dispersion of titanium vanadium boride ([Ti)V] x B y ) whiskers within an aluminum solvent metal matrix.
• Powders of Ti, B and Si in the proper stoichiometric proportions to produce an intermediate material comprising 50 weight percent TiB 2 second phase particles in a silicon solvent metal matrix are mixed and then compacted to 40 ksi.
• the compact is placed on a water cooled copper boat in a quartz tube under flowing argon and inductively heated to initiate an exothermic reaction.
• the resultant intermediate material comprises TiB 2 second phase particles dispersed in a silicon solvent metal matrix.
• Powders of Nb, B and Al in the proper stoichiometric proportions to produce an intermediate material comprising 50 weight percent NbB second phase particles in an aluminum solvent metal matrix are mixed and then compacted to 40 ksi.
• the compact is placed on a water cooled copper boat in a quartz tube under flowing argon and inductively heated to initiate an exothermic reaction,
• the resultant intermediate material comprises NbB second phase particles dispersed in an aluminum solvent metal matrix.
• Powders of Zr, B, AlN and Al in the proper stoichiometric proportions to produce an intermediate material comprising 25 weight percent ZrN particles and 25 weight percent ZrB 2 particles (50 total weight percent second phase) dispersed in an aluminum solvent metal matrix are mixed and then compacted to 40 ksi.
• the compact is placed on a water cooled copper boat in a quartz tube under flowing argon and inductively heated to initiate an exothermic reaction.
• the resultant intermediate material comprises ZrN and ZrB 2 second phase particles dispersed in an aluminum solvent metal matrix.
• Example 2 Intermediate material, produced as in Example 2, comprising 50 weight percent TiB 2 second phase particles in an aluminum solvent metal matrix is crushed, roughly mixed with crushed titanium sponge host metal and then mechanically compacted into blocks approximately 2 inches in diameter and 3 inches in height. Several of the compacts are welded together to form a consumable electrode. The electrode is subsequently arc-melted in a consumable electrode arc-melter under vacuum, using a water-cooled copper mold, to produce a final composite ingot comprising approximately 7 weight percent TiB 2 second phase particles dispersed in a Ti-45Al (55 atomic percent Ti, 45 atomic percent Al) final metallic matrix.
• Ti-45Al 55 atomic percent Ti, 45 atomic percent Al
• Example 2 Intermediate material, produced as in Example 2, comprising 60 weight percent TiB 2 second phase particles in an aluminum solvent metal matrix is crushed, roughly mixed with crushed titanium sponge host metal and then mechanically compacted into blocks approximately 2 inches in diameter and 3 inches in height. Several of the compacts are welded together to form a consumable electrode. Additional support is given to the electrode by welding pure titanium ods along the length of the electrode. The electrode is subsequently arc-melted in a consumable electrode arc-melter under vacuum, using a water-cooled copper mold, to produce a final composite ingot comprising approximately 7 weight percent TiB 2 second phase particles dispersed in a Ti-45Al (55 atomic percent Ti, 45 atomic percent Al) final metallic matrix.
• Ti-45Al 55 atomic percent Ti, 45 atomic percent Al
• Example 2 Intermediate material, produced as in Example 2, comprising 60 weight percent TiB 2 second phase particles in an aluminum solvent metal matrix is crushed, roughly mixed with crushed titanium sponge host metal and then mechanically compacted into blocks approximately 2 inches in diameter and 3 inches in height. Several of the compacts are welded together to form a consumable electrode. The electrode is subsequently arc-melted in a consumable electrode arc-melter under vacuum, using a water-cooled copper mold, to produce a first ingot comprising approximately 7 weight percent TiB 2 second phase particles dispersed in a Ti-45Al (55 atomic percent Ti, 45 atomic percent Al) metallic matrix.
• Ti-45Al 55 atomic percent Ti, 45 atomic percent Al
• This first ingot is subsequently used as an electrode and remelted in a consumable electrode arc-melter under vacuum, using a larger water-cooled copper mold, to yield a final composite ingot comprising about 7 weight percent TiB 2 second phase particles dispersed in a Ti-45Al (55 atomic percent Ti, 45 atomic percent Al) metallic matrix.
• the TiB 2 second phase particles of the final composite have an average size of about 3 microns, indicating that only a minor amount of particle growth occurred during the arc-melting procedure.
• the double-melted final composite ingot possesses improved uniformity and surface quality compared to the first, single-melted ingot.
• Example 26 is repeated, with the exception that an alloying addition of vanadium is mixed with the crushed intermediate material and Ti sponge prior to compaction.
• the resultant final composite ingot comprises a Ti-45Al-2V (53 atomic percent Ti, 45 atomic percent Al, 2 atomic percent V) final metallic matrix having approximately 7 weight percent TiB 2 second phase particles substantially uniformly dispersed therein.
• Example 26 is repeated, with the exception that the compacted electrode of intermediate material and host metal is sintered in either an inert or vacuum furnace for a period of up to 48 hours prior to arc-melting. A final composite is produced similar to that of Example 26.
• Example 26 is repeated, with the exception that the mixture of crushed intermediate material and host metal is isostatically pressed into a long rod to produce the electrode for arc-melting. A final composite is produced similar to that of Example 26.
• An intermediate material, prepared as in Example 12, comprising [Ti,Nb] x B y second phase whiskers in an aluminum solvent metal matrix is crushed and then mixed with another crushed intermediate material, prepared as in Example 17, comprising TiN second phase particles in an aluminum solvent metal matrix.
• This intermediate material mixture is roughly mixed with niobium host metal pellets and mechanically compacted to form a consumable electrode.
• the electrode is subsequently arc-melted in a consumable electrode arc-melter under vacuum, using a water-cooled copper mold, to produce a first ingot comprising approximately 8 total weight percent second phase particles (about 4 weight percent [Ti,Nb] x B y and 4 weight percent TiN) dispersed in a Nb 2 Al intermetallic matrix.
• This first ingot is subsequently used as an electrode and remelted in a consumable electrode arc-melter under vacuum, using a larger water-cooled copper mold, to yield a final composite ingot comprising about 8 total weight percent [Ti,Nb] x B y and TiN second phase particles substantially uniformly dispersed in a Nb 2 Al intermetallic matrix.
• Example 23 Intermediate material, produced in a manner similar to Example 23, comprising ZrN and ZrB 2 second phase particles dispersed in an aluminum solvent metal matrix is crushed, roughly mixed with zirconium host metal pellets and then mechanically compacted to form a consumable electrode.
• the electrode is subsequently arc-melted in a consumable electrode arc-melter under vacuum, using a water-cooled copper mold, to produce a first ingot comprising approximately 8 total weight percent ZrN and ZrB 2 second phase particles (4 weight percent ZrN and 4 weight percent ZrB 2 ) dispersed in an ZrAl 3 intermetallic matrix.
• This first ingot is subsequently used as an electrode and remelted in a consumable electrode arc-melter under vacuum, using a larger water-cooled copper mold, to yield a final composite ingot comprising about 8 total weight percent ZrN and ZrB 2 second phase particles dispersed in a ZrAl 3 matrix.
• Example 29 is repeated, with the exception that the TiB 2 /Al intermediate material is crushed to a fine powder and the titanium host metal is provided in the form of minus 325 mesh powder. A final composite is produced similar to that of Example 29.
• Example 33
• Example 32 is repeated, with the exception that the rod comprising compacted powders of TiB 2 /Al intermediate material and titanium host metal is arc-welded to form a weldment comprising a final composite similar to that of Example 32.
• Example 2 Intermediate material produced in a manner similar to Example 2, with the exception that the TiB 2 comprises 25 weight percent of the material, and is extruded to form a wire. The wire is then twisted with a titanium host metal wire and fed into the stream of a plasma spray gun. The resultant final composite comprises approximately 7 weight percent TiB 2 second phase particles dispersed in a titanium aluminide matrix.
• Example 34 is repeated, with the exception that the twisted wires of the TiB 2 /Al intermediate material and titanium host metal are arc-welded to form a weldment comprising a final composite similar to that of Example 34.
• 60 weight percent TiB 2 second phase particles in an aluminum solvent metal matrix is crushed and then added to a molten bath of aluminum, while stirring, to produce a second intermediate material comprising approximately 15 weight percent TiB 2 particles dispersed in an aluminum matrix.
• This second intermediate material is extruded to form a wire, twisted with a titanium host metal wire, and fed into the stream of a plasma spray gun.
• the resultant final composite comprises approximately 7.5 weight percent TiB 2 second phase particles dispersed in a titanium aluminide matrix.
• the present invention has a number of advantages over methods taught by the prior art. For example, this invention circumvents the need for micron sized, unaggl omerated ceramic starting materials, which materials are not typically commercially available, and are often pyrophoric. This invention also eliminates the technical problems of uniformly dispersing a second phase in a molten metal, and avoids the problem of oxide or other deleterious layer formation at the second phase/metal interface during processing.
• the final composites of the present invention also have improved high temperature stability, in that the second phase is substantially non-reactive with the final metallic matrix. Further, as opposed to composites presently available, the final.
• metallic-second phase composites of the present invention can be remelted and recast while retaining fine matrix grain size, fine second phase particle size, and the resultant superior physical properties of the material.
• the final composites may be welded without degradation of material properties, and after welding possess superior corrosion resistance, when compared to metal matrix composites presently available.
• the final composites of the present invention are capable of being formed by conventional ingot metallurgy techniques such as extruding, forging and rolling.
• the arc-melting process of the present invention also allows for the production of large, industrial quantities of metal-second phase composite materials, due to the fact that ingots of several thousand pounds may be produced in one arc-melting run.

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