EP0325179A1

EP0325179A1 - Process for producing tungsten heavy alloy sheet

Info

Publication number: EP0325179A1
Application number: EP89100602A
Authority: EP
Inventors: Walter A. Johnson; Preston B. Kemp, Jr.; James R. Spencer; Nelson E. Kopatz
Original assignee: GTE Products Corp
Current assignee: Osram Sylvania Inc
Priority date: 1988-01-14
Filing date: 1989-01-13
Publication date: 1989-07-26

Abstract

A process is disclosed for producing a sheet of tungsten heavy alloy which involves uniformly blending elemental powder components of the alloy by forming a slurry of the powder components in a liquid medium, removing the liquid medium from the powders and forming a planar cake of the powders, drying the cake, sintering the cake to a density equal to or greater than about 90% of the theoretical density of the alloy to form the sheet.

Description

BACKGROUND OF THE INVENTION

Tungsten heavy alloy sheet can be produced by rolling sintered slabs of the alloy. Because the rolling requires numerous anneals, it is desirable that the starting slab be no more than about twice the final thickness. One method to produce these slabs is by isostatically pressing the powder alloy blends and sintering them to full density. With thin slabs it is difficult to get a uniform fill of the mould so the resulting slabs are not uniform in thickness. There is also a problem with breakage with the thin slabs. Using this method it is not possible to produce slabs with a surface area to thickness ratio much over 600 or thickness less than about 0.5˝ (12.7 mm).
Another method of making tungsten heavy alloy sheet is to press large billets and cut the green billet into thin slabs. While this process produces slabs of uniform thickness it has the size limitations of the previous method and there is the added expense of cutting.
It would be desirable to make a sheet preform substantially close in thickness to the final thickness of the rolled sheet. This would reduce the time, energy, and labour required for hot rolling and annealing.
Furthermore, tungsten heavy alloy sheet is currently produced by powder consolidation using cold isostatic pressing followed by a series of alternate hot rolling and annealing steps. The sheet must be annealed after about each 30% reduction in thickness.
It would be desirable to make a sheet preform substantially close in thickness to the final thickness of the rolled sheet. This would reduce the time, energy, and labour required for hot rolling and annealing.
US Patent 2,735,757 relates to a process for forming iron metal powder from iron salts by oxidising a solution of the iron salts to produce a hydrate sludge of the iron, followed by reducing the iron to the metal powder.
US Patent 3,663,667 disclosed a process for producing multimetal alloy powders wherein an aqueous solution of at least two thermally reducible metallic compounds and water is formed, the solution is atomised into droplets having a droplet size below about 150 microns in a chamber that contains a heated gas whereby discrete solid particles are formed and the particles are thereafter heated in a reducing atmosphere and at temperatures from those sufficient to reduce the metallic compounds to temperature below the melting point of any of the metals in the alloy.
US Patent 4,348,224 relates to a process for producing fine cobalt metal powder by digesting cobalt bearing scrap in hydrochloric acid to produce an aqueous cobalt acid chloride solution containing copper and silver ions which are removed by cementation with iron to result in a cobalt chloride solution which is processed to fine cobalt metal powder.
US Patents 3,909,241 and 3,974,245 relate to free flowing powders which are produced by feeding agglomerates through a high temperature plasma reactor to cause at least partial melting of the particles and collecting the particles in a cooling chamber containing a protective gaseous atmosphere where the particles are solidified. In these patents, the powders are used for plasma coating and the agglomerated raw materials are produced from slurries of metal powders and binders.
This invention relates to a process for producing tungsten heavy alloy sheet in which a sintered cake is first formed which is substantially close in thickness to the final thickness of the rolled sheet.
Furthermore, this invention relates to a process for producing tungsten heavy alloy sheet by sintering a preform planar cake which is substantially close in thickness to the final thickness of the rolled sheet. More particularly, the cake is formed from metal powder particles each of which is an admixture of the alloying elements, the admixture having been hydrometallurgically produced from a solution of compounds of the metal values.
Furthermore, this invention relates to a process for producing tungsten heavy alloy sheet by sintering a preform planar cake which is substantially close in thickness to the final thickness of the rolled sheet. More particularly, the cake is formed from the component metal powders which have been produced by high temperatures processing, most preferably plasma melting rapid solidification (PMRS) techniques.

SUMMARY OF THE INVENTION

In accordance with the broadest aspect of this invention, there is provided a process for the producing of a sheet of tungsten heavy alloy which involves forming a slurry comprising at least the metal powder componenets of the alloy, removing any liquid from said slurry and forming a planar cake of the solid compounds of said slurry, thereafter drying the cake and sintering the cake to a density equal to or greater than about 90% of the theoretical density of the alloy to form the sheet.
In accordance with a second aspect of this invention, there is provided a process for producing a sheet of tungsten heavy alloy which involves uniformly blending elemental powder components of the alloy by forming a slurry of the powder components in a liquid medium, removing the liquid medium from the powders and forming a planar cake of the powder, drying the cake, sintering the cake to a density equal to or greater than about 90% of the theoretical density of the alloy to form the sheet.
In accordance with a third aspect of this invention, there is provided a process for producing a sheet of tungsten heavy alloy which involves uniformly blending metal powder components of the alloy by forming a slurry of the powder components and one or more chemical compounds of at least one of the components of the alloy as an inorganic binder in a liquid medium, the chemical compound being soluble in the liquid medium and capable of being decomposed into one or more of the metal components of the alloy below the melting point of the metal powder components, removing the liquid medium from the powder components and forming a planar cake of the powder components and said inorganic binder, drying the cake, heating the cake to a temperature sufficient to decompose the inorganic binders into their elemental components or oxides, followed by heating the cake in a reducing atmosphere at a temperature sufficient to reduce any oxides formed during the previous steps to the metals, and sintering the cake to a density equal to or greater than about 90% of the theoretical density of the alloy to form the sheet.
In accordance with a fourth aspect of this invention, there is provided a process for producing a sheet of tungsten heavy alloy which involves forming a solution of chemical compounds containing the metal values of the alloy in the correct proportion as in the alloy, crystallising the compounds from solution and drying the compounds, reducing the compounds to their respective metals wherein each particle is an admixture of the alloy componenets; forming a slurry of the metals and a liquid medium, removing the liquid medium from the metals and forming a planar cake of the metals, drying the cake, and sintering the cake to a density equal to or greater than about 90% of the theoretical density of the alloy to form the sheet.
In accordance with a fifth aspect of this invention, there is provided a process for producing a sheet of tungsten heavy alloy which comprises forming metal particles of the alloy wherein each metal particle is a uniform admixture of the alloy components, entraining the particles in a carrier gas, passing the particles and the carrier gas into a high temperature zone at a temperature above the melting point of the matrix phase of the particles and maintaining the particles in the zone for a sufficient time to melt at least the matrix phase of the particles and form spherical particles, followed by rapidly and directly solidifying the high temperature treated material while the material is in flight. A slurry is formed of this high temperature treated material and a liquid medium, the liquid medium is removed from the material and a planar cake is formed of the material, the cake is dried, and sintered to a density equal to or greater than about 90% of the theoretical density of the alloy to form the sheet.
In accordance with a sixth spect of this invention, there is provided a process for producing a sheet of tungsten heavy alloy which involves uniformly blending elemental metal powder componentss of the alloy by forming a slurry of the powder components in a liquid medium, introducing the slurry onto a filter medium and applying the vacuum to the bottom of the slurry to form a planar cake of the powder components. The cake is then dried and sintered to a density equal to or greater than about 90% of the theoretical density of the alloy to form the sheet.

DETAILED DESCRIPTION OF THE INVENTION

For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above description of some of the aspects of the invention.
The process of the present invention relates to formation of a planar cake of the component powders of the tungsten heavy alloy. This cake can then be processed to form a sintered sheet which is substantially close in thickness to the final thickness of the rolled sheet. As a result of formation of this type of cake, there is a reduction in the time, energy and labour required for hot rolling and annealing.
Some tungsten heavy alloys which are especially suited to this invention, although the invention is not limited to these, are tungsten-iron-nickel alloys especially those in which the Ni:Fe weight ratio is from about 1:1 to about 9:1 and most preferably about 8:2. As an example of these preferred alloys are those having the following composition in percent by weight: about 8% Ni, about 2% Fe, and the balance W, about 4% Ni, about 1% Fe, and the balance W, and about 5.6% Ni, about 1.4% Fe, and the balance W. The alloys can be with or without additions of Co and/or Cu.
In accordance with the first (broadest) and second aspects of this invention, the elemental metal powder components of the alloy are first uniformly blended. This is done by forming a slurry of the powders in a liquid medium. The liquid medium can be water or organic solvents, which can be oxygen containing or non-oxygen containing organic solvents. Typical oxygen containing organic solvents are alcohols, one in particular being a reagent alcohol which is about 90% by weight ethyl alcohol, about 5% by weight methyl alcohol, and about 5% by weight isopropyl alcohol. Other solvents that can be used are alkane hydrocarbon liquids and chlorinated hydrocarbon liquids. The slurry can have other components such as organic or inorganic binders, etc. The actual formation of the slurrycan be done by standard methods.
The liquid medium is then removed from the powders. This is done in such a way so that the powders form into a planar cake which is substantially close in thickness to the thickness of the final rolled sheet. The thickness of the sheet is typically from about 0.1" (2.54mm) to about 0.5" (12.7mm) after sintering and before rolling. By a planar cake is meant that the cake is uniform in thickness and density and is uniform in composition across the length and width of the cake. At this point, the composition of the cake may not be completely uniform throughout the thickness because tungsten powder would tend to settle faster than the other components. However, during the subsequent sintering step, compositional variations essentially disappear and the composition becomes substantially uniform throughout its thickness. The preferred methods of forming the planar cake are by using a porous filter medium and applying vacuum, gas pressure, or mechanical pressure. Vibration can also be used if this is desirable. The liquid removal can be accomplished by batch or continuous processing.
The resulting planar cake is then dried by conventional powder metal drying methods to remove essentially all the liquid therefrom, the methods being selected to reduce or eliminate cracking during drying. Any organic binders which may be present are removed by standard dewaxing techniques.
At this point, if the liquid medium of the slurry has been water or an oxygen containing organic solvent, oxygen must be removed from the cake. This is done by heating the cake in hydrogen at a temperature sufficient to reduce any metal oxides which are present to their respective metals but below the normal sintering temperature of any metal contained therein. By "normal sintering temperature" is meant the temperature at which the cake is sintered to the final desired density. A minor amount of sintering can take place at this point and this is advantageous because it strengthens the cake and it is easier to handle if handling is necessary. This temperature is most typically from about 800°C to about 1000°C. The time of heating depends on factors as the temperature, size of charge, thickness of the cake, nature of the equipment, etc. This step can be done separately or as part of the sintering operation.
The resulting dried and heated cake is then sintered by well known methods to a density at or near the theoretical density. This is considered to be equal to or greater than about 90% of the theoretical density of the alloy. Depending on the application and on the composition, the cake can be solid state or liquid phase sintered to form the sheet. For example, if the sheet is to be rolled, it is necessary to get the density to at least about 90% to about 93% of the theoretical. With a weight composition consisting essentially of about 7% Ni, about 3% Fe, and about 90% W, solid state sintering would be sufficient. Sintering temperatures and times depend on the nature of the alloy and on the density desired for the specific application. Typically, the solid state sintering temperature is from about 1400°C to about 1430°C. Liquid phase sintering is preferable for better rolling, higher density and healing of cracks which can form during drying. Densities of about 99.4% of theoretical have been achieved in practice. Usually liquid phase sintering results in a more uniform composition of the alloy components throughout the sheet. The liquid phase sintering temperature is above the solidus temperature of the matrix phase of the alloy but below the melting point of tungsten.
The resulting sheet can now be processed by known methods of hot rolling and annealing to form the final size sheet. However, when the process of the present invention is followed to produce a sheet which is close to the desired final thickness, less rolling and annealing are required than with sheets formed by prior art methods. This is because the cake has been formed to a size very close to the desire size of the final sheet.
To more fully illustrate the first and second aspects of this invention, the following non-limiting example is presented.

Example 1

This example is a comparison of how a sintered preform made by prior art methods is rolled to final dimensions versus a preform sheet made by the process of the present invention.

Prior art method Sintered preform (cold isostatic press and sinter)	This invention Sintered preform
1" (25.4mm) thick	0.1786" (4.52mm) thick
Heat treat	Heat treat
Roll to reduce to 0.7" (17.8mm) thick (30% reduction)	Roll to reduce to 0.125" (3.17mm) (30% reduction)
Anneal (1 hr)	Heat treat
Roll to reduce to 0.49" (12.44mm) (30% reduction)	Trim to size
Anneal (1 hr)
Roll to reduce to 0.343" (8.7mm) (30% reduction)
Anneal (1 hr)
Roll to reduce to 0.240" (6.1mm) (30% reduction)
Anneal (1 hr)
Roll to reduce to 0.168" (4.26mm) (30% reduction)
Anneal (1 hr)
Roll to reduce to 0.125" (3.17mm) (30% reduction)
Heat treat
Trim to size

It can be seen that by the process of the present invention in forming the preform sheet, a number of rolling and annealing steps are eliminated.
In accordance with the third aspect of this invention, the elemental metal powder components of the alloy are first uniformly blended. This is done by forming a slurry of the powders in a liquid medium. The liquid medium can be water or a non-aqueous solvent. Typical non-aqueous solvents are alcohol, one in particular being reagent alcohol which is about 90% by weight ethyl alcohol, about 5% by weight methyl alcohol, and about 5% by weight isopropyl alcohol. Also added to and made part of the slurry is a chemical compound of at least one of the components of the alloy which serves as an inorganic binder or binders. The chemical compound must be soluble in the liquid medium and be capable of being decomposed below the melting point of the metal powder components into the element or elements of the alloy. In accordance with a preferred embodiment, the chemical compounds can be one or more of those of tungsten, iron and nickel. Preferred compounds salts which work especially well in the process of the present invention are ammonium paratungstate, ammonium metatungstate, iron chloride, nickel chloride, iron hydroxide, nickel hydroxide, iron oxalate, and nickel oxalate.
The actual formation of the slurry can be done by standard methods such as mixing and stirring the solids into the liquid medium with the amount of the liquid medium being sufficient to allow agitation of the slurry but not excessive so that the process becomes impractical.
The liquid medium is then removed from the powders as described above with regard to the first and second aspects.
As has been stated previously, the chemical compounds which serve as the inorganic binders are soluble in the slurry liquid medium. Therefore, when the metal solids are removed from the bulk of the slurry medium, a relatively small amount of the solution containing the dissolved binders remains on the metals. After the drying, the inorganic compound or compounds serve to bind the metal particles together. Since the amount of binder is relatively small, upon subsequent reduction of these binders to their metals, the composition of the alloy is not typically changed to any significant degree.
The resulting planar cake is then dried by conventional or modifications of conventional powder metal drying methods to remove essentially all the liquid therefrom. The methods are selected to reduce or eliminate cracking of the cake during drying.
The cake is heated in a non-oxidising, that is, a reducing or non-reacting, atmosphere at a temperature sufficient to decompose the inorganic salts into their component elements or oxides. When the preferred chemical compounds of ammonium paratungstate and ammonium metatugstate are used, they are decomposed into tungsten. Because they contain no other contaminating elements, there is no residue left after the decomposition. This is an advantage over organic binders which leave an undesirable carbonaceous residue after the dewaxing step. When ammonium paratungstate and ammonium metatungstate are used as binders, they are decomposed at temperatures of from about 200°C to about 800°C.
In actual practice the above described drying and heating steps can be done in one operation if this is convenient.
The resulting dried and heated cake is then reduced by heating in a reducing atmosphere such as hydrogen to ensure the essentially complete reduction of any compounds or oxides which may have formed in the previous operations to the respective metals. The reduction is done below the normal sintering temperature of any metal contained therein. By "normal sintering temperature" is meant the temperature at which the cake is sintered to the final desired density. A minor amount of sintering can take place at this point and it is advantageous because it strengthens the cake and the cake is easier to handle if handling is necessary. This temperature is normally from about 800°C to 1000°C. The time of heating depends on factors as the temperature, size of charge, thickness of the cake, nature of the equipment, etc
The resulting dried and heated cake is then sintered by well known methods to a density at or near the theoretical density. This is considered to be equal to or greater than about 90% of the theoretical density of the alloy. Depending on the application and on the composition the cake can be solid state or liquid phase sintered to form the sheet. for example, if the sheet is to be rolled, it is necessary to get the densityto at least about 90% to about 93% of the theoretical density. With a weight composition consisting essentially of about 7% Ni, about 3% Fe, and about 90% W, solid state sintering would be sufficient. Sintering temperatures and times depend on the nature of the alloy and on the density desired for the specific application. In the example above, the solid state sintering temperature is from about 1400°C to about 1430°C. Liquid phase sintering is preferable for better rolling, higher density and healing of cracks which can form during drying. Densities of about 99.4% of the theoretical have been achieved in practice. Usually the liquid phase sintering results in a more uniform composition of the alloy components throughout the sheet. The liquid phase sintering temperature is above the solidus temperature of the matrix phase of the alloy but below the melting point of tungsten.
The resulting sheet can now be processed by known methods of hot rolling and annealing to form the final size sheet. However, when the process of the present invention is followed to produce the pre-rolled and pre-annealed sheet, less rolling and annealing are required than with sheets formed by prior art methods. This is because the cake has been formed to a size very close to the desired size of the final sheet.
The process of the present invention (according to the fourth aspect thereof) relates to a process for producing tungsten heavy alloy sheet by first crystallising from solution chemical compounds containing metal values of the alloy. The compounds are reduced to the metals in the form of an admixture of the alloy components by virtue of the crystallisation from solution. A planar cake is then formed of the admixture of hydrometallurgically produced powders via formation of a slurry and removing the liquor. The cake is then sintered to form the sheet which can then be further rolled and annealed. This cake can then be processed to form a sheet which is substantially close in thickness to the final thickness of the rolled sheet. As a result of formation of this type of cake, there is a reduction in time, energy and labour required for hot rolling and annealing.
Some tungsten heavy alloys which are especially suited to this invention are tungsten-iron-nickel alloys especially those in which the Ni:Fe weight ratio is from about 1:1 to about 9:1 and most preferably about 8:2. As an example of these preferred alloys are those having the following compositions in percent by weight: about 8% Ni, about 2% Fe, and the balance W, about 4% Ni, about 1% Fe, and the balance W, and about 5.6% Ni, about 1.4% Fe, and the balance W. The alloys can be with or without additions of Co and/or Cu.
A solution is first formed of chemical compounds containing metal values of the alloy in the correct proportion as in the alloy. This can be done by any technique, such as by dissolving the compounds as is, in solution.
In accordance with one embodiment of the fourth aspect, the elemental metal powder components of the alloy are first dissolved in an acid solution. Calculation of the required relative amounts of the elemental powders is determined by the composition of the alloy to be produced. Dissolution of metal values in acid solution and calculation of the amounts of metal required for the alloy composition can be done by anyone sskilled in the art. The acid can be a mineral acid such as hydrochloric, sulphuric and nitric acids or an organic acid such as acetic, formic and the like. Hydrochloric acid is especially preferred because of cost and availability. As a result of the acid dissolution of the metal powders, compounds of the respective metals are formed as precipitates. Those skilled in the art would know how to dissolve metal values in acid solution in the correct proportions.
In accordance with another embodiment of the fourth aspect, nickel powder and iron powder are dissolved in hydrochloric acid. A concentrated solution of ammonium metatungstate is added to the hydrochloric acid solution of nickel and iron. The amounts of iron, nickel and tungsten have been calculated to be the proper amounts to result in the desired alloy composition. The pH of the resulting solution is raised to the basic side, usually to a pH of about 6.5 to about 7.5 with ammonia or ammonium hydroxide to precipitate the tungsten as ammonium paratungstate (APT) and the iron and nickel as their hydroxides.
The resulting compounds are then removed from solution. This is done by any standard technique such as filtration of the precipitate of the compounds which has formed. In this case, the compounds are then dried. Alternately, if the compounds are highly soluble as is the case when ammonium metatungstate is one of the compounds, the solution can be spray dried to crystallise the compounds.
The compounds, if they are insoluble in water, can then be water washed if desired to remove any contaminants.
The compounds are then reduced to the metals. This is done by standard reduction techniques. For example, the reduction to the metals can be done in one step or in more than one step. As an example of the latter, the compounds which can be predried are first heated to decompose them into their oxides. Temperature depends on the nature of the metals. Time depends on the nature of the metals, temperature, amount of material being processed, the equipment, etc. Anyone skilled in the art would know how to reduce the compounds to the metals. In the case of ammonium paratungstate (APT), iron hydroxide and nickel hydroxide, the reduction is done as follows. The reduction furnace is slowly ramped from room temperature to almost about 275°C to remove ammonia and water vapour from the APT to form WO₃. The remperature is next ramped to 750°C to about 800°C to reduce the hydroxides and oxides to their respective metals. As a result of the reduction of the hydrometallurgically produced compounds, each of the resulting metal particles is an admixture in itself of all the component metals which form the alloy.
A slurry of the resulting hydrometallurgically produced metal powders is then formed in a liquid medium. The liquid medium can be water or organic solvents, which can be oxygen containing organic solvents or non-oxygen containing organic solvents. Typical oxygen containing organic solvents are alcohols, one in particular being a reagent alcohol which is about 90% by weight ethyl alcohol, about 5% by weight methyl alcohol, and about 5% by weight isopropyl alcohol. Other solvents that can be used are alkane hydrocarbon liquids and chlorinated hydrocarbon liquids. The slurry can have other components such as organic or inorganic binders, etc. The actual formation of the slurry can be done by standard methods.
The liquid medium is then removed from the metal powders. This is done in such a way so that the powders form into a planar cake which is substantially close in thickness to the thickness of the final rolled sheet. The thickness of the sheet is typically from about 0.1" (2.54mm) to about 0.5" (12.7mm) after sintering and before rolling. By a planar cake is meant that the cake is uniform in thickness and density across the length and width of the cake. The cake is uniform in composition throughout by virtue of the fact that each particle is an admixture of the alloy components. The preferred methods of forming the planar cake are by using a porous filter medium and applying vacuum, gas pressure, or mechanical pressure. Vibration can also be used if this is desirable. The liquid removal can be accomplished by batch or continuous processing.
The resulting cake is then dried by conventional powder metal drying methods to remove essentially all the liquid therefrom, the methods being selected to reduce or eliminate cracking during drying. Any organic binders which may be present are removed by standard dewaxing techniques.
At this point, if the liquid medium of the slurry has been water or an oxygen containing organic solvent, oxygen must be removed from the cake. This is done by heating the cake in hydrogen at a temperature sufficient to reduce any metal oxides which are present to their respective metals but below the normal sintering temperature of any metal contained therein. By "normal sintering temperature" is meant the temperature at which the cake is sintered to the final desired density. A minor amount of sintering can take place at this point and this is advantageous because it strengthens the cake and it is easier to handle if handling is necessary. This temperature is most typically from about 800°C to about 1000°C. The time of heating depends on factors as the temperature, size of charge, thickness of the cake, nature of the equipment, etc.
The resulting dried and heated cake is then sintered by well known methods to a density at or near the theoretical density. This is considered to be equal to or greater than about 90% of the theoretical density of the alloy. Depending on the application and on the composition, the cake can be solid state or liquid phase sintered to form the sheet. For example, if the sheet is to be rolled, it is necessary to get the density to at least about 90% to about 93% of the theoretical. With a weight composition consisting essentially of about 7% Ni, about 3% Fe, and about 90% W, solid state sintering would be sufficient. Sintering temperatures and times depend on the nature of the alloy and on the density desired for the specific application. In the example above, the solid state sintering temperature is from about 1400°C to about 1430°C. Liquid phase sintering is preferable for better rolling, higher density and healing of cracks which can form during drying. Densities of about 99.4% of theoretical have been achieved in practice. Usually liquid phase sintering results in a more uniform composition of the alloy components throughout the sheet.
The resulting sheet can now be processed by known methods of hot rolling and annealing to form the final size sheet. However, when the process of the present invention is followed to produce the pre-rolled and pre-annealed sheet, less rolling and annealing are required than with sheets formed by prior art methods. This is because the cake has been formed to a size which is very close to the desired size of the final sheet. The liquid phase sintering temperature is above the solidus temperature of the matrix phase of the alloy but below the melting point of tungsten.
To more fully illustrate this fourth aspect of the invention, the following non-limiting example 2 is presented. All parts, portions and percentages are on a weight basis unless otherwise stated.

Example 2

About 60 parts of Ni powder are dissolved in about 240 parts of concentrated hydrochloric acid and about 200 parts of water. About 25.5 parts of Fe powder is dissolved in about 120 parts of concentrated hydrochloric acid and about 100 parts of water. The resulting solutions are combined. About 1103 parts of ammonium metatungstate are dissolved in about 1000 parts of water and the resulting concentrated solution is combined with the iron-nickel acid solution. The pH is raised to about 6.5 to 7.5 with ammonium hydroxide to precipitate APT, and the nickel and iron hydroxides which are then filtered off. The resulting precipitate is then reduced to the metals as follows. The reduction furnace is slowly ramped from room temperature to almost about 275°C to remove ammonia and water vapour from the APT to form WO₃. The temperature is next ramped to 750°C to about 800°C to reduce the hydroxides and oxides to their respective metals. As a result of reducing compounds which have been hydrometallurgically produced from solution, each of the resulting metal particles is an admixture in itself of all the component metals which form the alloy. A slurry of the precipitate is then formed. The solids are then removed from the liquid medium in the form of a planar cake. The cake is then dewaxed to remove binders. The cake is then sintered.
The process of the fifth aspect of the present invention relates to a process for producing tungsten heavy alloy sheet with component metal powders of the alloy as the starting material. Particles are formed of the component alloy metal powders so that each particle is itself a uniform admixture of the alloy components in the propertions in which they are in the alloy. These particles are then high temperature processed such as by PMRS techniques to produce spherical alloy particles which are then slurried to produce a planar cake which is very close in dimension to the sheet to be formed. The cake is then sintered to form the sheet. The sheet can then be rolled and annealed as necessary to produce the final dimensions. As a result of formation of this type of cake, there is a reduction in time, energy and labour required for hot rolling and annealing.
Some tungsten heavy alloys which as especially suited to this invention, although the invention is not limited to these, are tungsten-iron-nickel alloys especially those in which the Ni:Fe weight ratio is from about 1:1 to about 9:1 and most preferably about 8:2. As an example of these preferred alloys are those having the following composition in percent by weight: about 8% Ni, about 2% Fe, and the balance W, about 4% Ni, about 1% Fe, and the balance W, and about 5.6% Ni, about 1.4% Fe, and the balance W. The alloys can be with or without additions of Co and/or Cu.
The mixture of metal powder particles in which each particle is a uniform admixture of the alloy components can be formed by any method. However, some of the preferred methods of obtaining this type of mixture are described below.
In accordance with one embodiment of the fifth aspect, the mixture can be formed by agglomerating the metal powder particle components with an organic binder.
This can be done by methods known in the art such as by spray drying, etc. Typical binders include waxes, polymers, and others which are known in the art. Each agglomerate thus formed is considered to be a particle which is the admixture of the alloy components. The organic binder or binders are then removed from the agglomerates by standard dewaxing techniques. The resulting dewaxed agglomerates are sintered by known methods to impart strength to the agglomerates. The sintering conditions will depend on the nature of the components and one skilled in the art would be able to carry out this step.
In accordance with another embodiment of the fifth aspect, the mixture can be formed by hydrometallurgical techniques. In this technique, a solution is formed of chemical compounds containing the metal values of the alloy in the correct proportion as in the alloy. This can be done by any technique, such as by dissolving the compounds as is in solution.
In accordance with one method of making the solution, the elemental metal powder components of the alloy are first dissolved in an acid solution. Calculation of the required relative amounts of the elemental powders is determined by the composition of the alloy to be produced. Dissolution of the metal values in acid solution and calculation of the amounts of metal required for the alloy composition can be done by anyone skilled in the art. The acid can be a mineral acid such as hydrochloric, sulphuric or nitric acids or an organic acid such as acetic, formic, and the like. Hydrochloric acid is especially preferred because of cost and availability. As a result of the acid dissolution of the metal powders, compounds of the respective metals are formed as precipitates. Those skilled in the art would know how to dissolve metal values in acid solution in the correct proportions.
In accordance with another preferred method of making the solution, nickel powder and iron powder are dissolved in hydrochloric acid. A concentrated solution of ammonium metatungstate is added to the hydrochloric acid solution of nickel and iron. The amounts of iron, nickel and tungsten have been calculated to be the proper amounts to result in the desired alloy. The pH of the resulting solution is raised to the basic side, usually to a pH of about 6.5 to about 7.5 with ammonia or ammonium hydroxide to precipitate the tungsten as ammonium paratungstate (APT) and the iron and nickel as their hydroxides.
The resulting compounds are then removed from solution. This is done by any standard technique such as by filtration of a precipitate that has formed. In this case, the precipitate of the compounds is dried. Alternatively, if the compounds are highly soluble as is the case when ammonium metatungstate is one of the compounds, the solution can be spray dried to crystallise the compounds.
The compounds, if they are insoluble in water can then be water washed if desired to remove any contaminants.
The compounds are then reduced to their respective metals to obtain the admixture. This is done by standard reduction techniques. For example, the reduction to metals can be done in one step or more than one step. As an example of the latter, the compounds which can be pre-dried if desired are first heated to decompose them into their oxides. Temperature depends on the nature of the metals. Time depends on the nature of the metals, temperature, amount of material being processed, the nature of the equipment, etc. In the preferred case of ammonium paratungstate (APT), iron hydroxide and nickel hydroxide, the reduction furnace is slowly ramped from room temperature to almost about 275°C to remove ammonia and water vapour from the APT to form WO₃. The temperature is next ramped to 750°C to about 800°C to reduce the hydroxides and oxides to their respective metals. As a result of reducing compounds which have been hydrometallurgically produced from solution, each of the resulting metal particles is an admixture in itself of all the component metals which form the alloy. Sintering is not necessary because by hydrometallurgical processing the alloy components are bound together.
The resulting sintered agglomerates or reduced powder particles, depending on which method was used to produce the admixture are now high temperature processed as follows to spheroidise the major portion of them. The particles are entrained in a carrier gas such as argon and passed through a high temperature zone at a temperature above the melting point of the particles and maintained in the high temperature zone for a sufficient time to melt at least the matrix phase of the particles and form essentially spherical particles. The preferred high temperature zone is a plasma.
Details of the principles and operation of plasma reactors are well known. The plasma has a high temperature zone, but in cross section the temperature can vary from about 5500°C to about 17,000°C. The outer edges are at low temperatures and the inner part is at a higher temperature. The retention time depends upon where the particles entrained in the carrier gas are injected into the nozzle of the plasma gun. Thus, if the particles are injected into the outer edge, the retention time must be longer, and if they are injected into the inner portion, the retention time is shorter. The residence time in the plasma flame can be controlled by choosing the point at which the particles are injected into the plasma. Residence time in the plasma is a function of the physical properties of the plasma gas and the powder particles themselves for a given set of plasma operating conditions and powder particles. Larger particles are more easily injected into the plasma while smaller particles tend to remain at the outer edge of the plasma jet or are deflected away from the plasma jet.
As the material passes through the plasma and cools, it is rapdily and directly solidified. Generally, the major weight portion of the material is converted to spherical particles. Generally greater than about 75% and most typically about 65% by weight of the material is converted to spherical particles by the high temperature treatment. Nearly 100% conversion to spherical particles can be attained.
A slurry of the resulting high temperature treated material and a liquid medium is formed. The liquid medium can be water or organic solvents, which can be oxygen containing or non-oxygen containing organic solvents. Typical oxygen containing organic solvents are alcohols, one in particular being a reagent alcohol which is about 90% by weight ethyl alcohol, about 5% by weight methyl alcohol, and about 5% by weight isopropyl alcohol. Other solvents that can be used are alkane hydrocarbon liquids and chlorinated hydrocarbon liquids. The slurry can have other components such as organic or inorganic binders, etc. The actual formation of the slurry can be done by standard methods.
The liquid medium is then removed from the material. This is done in such a way so that the material forms into a planar cake which is substantially close in thickness to the thickness of the final rolled sheet. The thickness of the sheet is typically from about 0.1" (2.54mm) to about 0.5" (12.7mm) after sintering and before rolling. By a planar cake is meant that the cake is uniform in thickness and density across the length and width of the cake. The cake is uniform in composition throughout by virtue of the fact that each particle is an admixture of the alloy components. The preferred methods of forming the planar cake are by using a porous filter medium and applying vacuum, gas pressure, or mechanical pressure. Vibration can also be used if this is desirable. The liquid removal can be accomplished by batch or continuous processing.
The resulting cake is then dried by conventional powder metal drying methods to remove essentially all of the liquid therefrom, the methods being selected to reduce or eliminate cracking during drying. Any organic binders which may be present are removed by standard dewaxing techniques.
At this point, if the liquid medium has been water or an oxygen containing organic solvent, oxygen must be removed from the cake. This is done by heating the cake in hydrogen at a temperature sufficient to reduce any metal oxides which are present to their respective metals but below the normal sintering temperature of any metal contained therein. By "normal sintering temperature" is meant the temperature at which the cake is sintered to the final desired density. A minor amount of sintering can take place at this point and this is advantageous because it strengthens the cake and it is easier to handle if handling is necessary. This temperature is most typically from about 800°C to about 1000°C. The time of heating depends on factors as the temperature, size of charge, thickness of the cake, nature of the equipment, etc.
The resulting dried and heated cake is then sintered by well known methods to a density at or near the theoretical density. This is considered to be equal to or greater than about 90% of the theoretical density of the alloy. Depending on the application and on the composition, the cake can be solid state or liquid phase sintered to form the sheet. For example, if the sheet is to be rolled, it is necessary to get the density to at least about 90% to about 93% of the theoretical. With a weight composition consisting essentially of about 7% Ni, about 3% Fe, and about 90% W, solid state sintering would be sufficient. Sintering temperatures and times depend on the nature of the alloy and on the density desired for the specific application. In the example above, the solid state sintering temperature is from about 1400°C to about 1430°C. Liquid phase sintering is preferable for better rolling, higher density and healing of cracks which can form during drying. Densities of about 99.4% of theoretical have been achieved in practice. Usually liquid phase sintering results in a more uniform composition of the alloy components throughout the sheet.
The resulting sheet can now be processed by known methods of hot rolling and annealing to form the final size sheet. However, when the process of the present invention is followed to produce the sintered sheet preform, less rolling and annealing are required than with sheets formed by prior art methods. This is because the cake has been formed to a size very close to the desired size of the final sheet. The liquid phase sintering temperature is above the solidus temperature of the matrix phase of the alloy but below the melting point of the tungsten.
The sixth aspect of this invention is described in the following with reference to the drawings, of which

Figure 1 is an overall view of a preferred filtration apparatus used to form the planar cake;
Figure 2 is a drawing showing how the slurry on the filter medium is vibrated and the movement of the gas out of the slurry;
Figure 2a is a drawing showing the layering of the atmosphere, liquid medium, and settled powder on the filter medium;
Figure 3 is a drawing showing the levelling of the slurry with a doctor blade;
Figure 4 is a drawing showing the removal of liquid medium from the slurry;
Figures 5a, 5b, 5c, and 5d are drawings showing the steps in removing the planar cake from the filtration apparatus; and
Figure 6 is a drawing showing an arrangement of the doctor blade and the vacuum unit of another filtration apparatus of this invention.

Some tungsten heavy alloys which are especially suited to the sixth aspect of the invention, although the invention is not limited to these, are tungsten-iron-nickel alloys especially those in which the Ni:Fe weight ratio is from about 1:1 to about 9:1 and most preferably about 8:2. As an example of these preferred alloys are those having the following composition in percent by weight: about 8% Ni, about 2% Fe, and the balance W, about 4% Ni, about 1% Fe, and the balance W, and about 5.6% Ni, about 1.4% Fe, and the balance W. The alloys can be with or without additions of Co and/or Cu.
The elemental metal powder components of the alloy are first uniformly blended. This done by forming a slurry of the powders in a liquid medium. The liquid medium can be water or organic solvents, which can be oxygen or non-oxygen containing organic solvents. Typical oxygen containing organic solvents are alcohols, one in particular being a reagent alcohol which is about 90% by weight ethyl alcohol, about 5% by weight methyl alcohol, and about 5% by weight isopropyl alcohol. Other solvents that can be used are alkane hydrocarbon liquids and chlorinated hydrocarbon liquids. The slurry can have other components such as organic or inorganic binders, etc. The actual formation of the slurry can be done by standard methods.
The liquid medium is then removed from the powders by applying vacuum to the bottom of a porous filter medium beneath the slurry. Vibration can also be used if this is desirable. Vibration can be applied before or during application of vacuum. This is done in such a way so that the powders form into a planar cake which is substantially close in thickness to the thickness of the final rolled sheet. The thickness of the sheet is typically from about 0.1" (2.54mm) to about 0.5" (12.7mm) after sintering and before rolling. By a planar cake is meant that the cake is uniform in thickness and density and is uniform in composition across the length and width of the cake. At this point, the composition of the cake may not be completely uniform throughout the thickness because tungsten powder would tend to settle faster than the other components. However, during the subsequent sintering step, compositional variations essentially disappear and the composition becomes substantially uniform throughout its thickness. The liquid removal can be accomplished by batch or continuous processing.
A typical filtration apparatus for forming the planar cake by the above described preferred procedure is shown in Figure 1 as (10). A container or drum (12) is shown with its top (14) through which there is an opening. Over this opening is a filter media (16). The filter media is usually porous plastic or preferably stainless steel filter cloth. The filter media is level and has no wrinkles. The preferred means of mounting the filter media to the container top is a frame shown as (18), the shape of which defines the shape of the cake which is to be formed. The frame is preferably made from PVC sheet of sufficient thickness to secure the filter media to the top of the container and to hold the shape of the cake. The thickness of the frame usually depends on the desired thickness of the cake. The slurry is introduced onto the filter media (16). The liquid medium passes through the media into the inside of the container (12). The powder settles onto the filter media. During the filtration, vacuum is applied from a conventional vacuum source as shown by the vacuum line connection (20), with vent (22) to atmosphere or gas source which allows the top to be released from the container. The frame is releasably mounted to the container top such as by bolts. Figure 2 shows how the slurry (24) on the filter medium is vibrated and the movement (shown by the arrows) of entrapped gas (26) out of the slurry. The slurry is vibrated in the vertical plane and trapped gas bubbles (26) consolidate and move to the top of the slurry. Figure 2a shows the layering of the gas or atmosphere (26), liquid medium (28) and settled powder (30) on the filter media (16) after the vibration. The settled powder of which the cake is to be formed is retained on the filter media. Figure 3 shows the levelling of the slurry (24) with a doctor blade (32). Figure 4 shows removal of the liquid medium from the slurry to form the cake (34). Arrows indicate the direction of the liquid medium directed out from the bottom of the slurry. Figures 5a, 5b, 5c and 5d show the steps of removal of the planar cake (34) from the filtration apparatus. Figure 5a shows a ceramic coated molybdenum substrate sheet (36) clamped to the top of the filter frame (18). Figure 5d shows the layering of the molybdenum sheet showing the zirconia coating (38), the molybdenum (40), and the cake (34). Figure 5b shows the resulting assembly of filter media, cake, filter frame and substrate having beeing inverted and vibration in the vertical plane allows the cake to be released onto the substrate sheet. Figure 5c shows the final planar cake (34) resting on the substrate sheet (36) after the filter frame is removed.
In accordance with another embodiment of the sixth aspect, the slurry is introduced onto a device which holds a filter medium which is usually rectangular in shape just before a doctor blade which levels the cake as it forms. A vacuum unit underneath and in contact with the filter medium applies a vacuum in a relatively narrow strip across the entire width of the cake just behind the doctor blade. Both the upper and lower portions of the above device move across the filter material to form a damp cake which is level across its width and length. Figure 6 shows an arrangement of the doctor blade (42) and the vacuum unit (44) in the filtration apparatus. The slurry (46) being agitated by agitating means (48) in a container or slurry tank (50) and being poured onto filter media (52) and being levelled with doctor blade as described above. After the cake (54) is formed, it is removed from the filter medium. This is done preferably by removing the device and clamping a ceramic coated molybdenum substrate to the filter which will serve as the support for the cake. The entire unit is inverted and the cake is released onto the substrate, with the aid of vibration if necessary.
The resulting planar cake is then dried by conventional powder metal drying methods to remove essentially all the liquid therefrom, the methods being selected to reduce or eliminate cracking during drying. Any organic binders which may be present are removed by standard dewaxing techniques.
At this point, if the liquid medium of the slurry has been water or an oxygen containing organic solvent, oxygen must be removed from the cake. This is done by heating the cake in hydrogen at a temperature sufficient to reduce any metal oxides which are present to their respective metals but below the normal sintering temperature of any metal contained therein. By "normal sintering temperature" is meant the temperature at which the cake is sintered to the final desired density. A minor amount of sintering can take place at this point and this is advantageous because it strengthens the cake and it is easier to handle if handling is necessary. This temperature is most typically from about 800°C to about 1000°C. The time of heating depends on factors as the temperature, size of charge, thickness of the cake, nature of the equipment, etc. This step can be done separately or as part of the sintering operation.
The resulting dried and heated cake is then sintered by well known methods to a density at or near the theoretical density. This is considered to be equal to or greater than about 90% of the theoretical density of the alloy. Depending on the application and on the composition, the cake can be solid state or liquid phase sintered to form the sheet. For example, if the sheet is to be rolled, it is necessary to get the density to at least about 90% to about 93% of the theoretical. With a weight composition consisting essentially of about 7% Ni, about 3% Fe, and about 90% W, solid state sintering would be sufficient. Sintering temperatures and times depend on the nature of the alloy and on the density desired for the specific application. Typically, the solid state sintering temperature is from about 1400°C to about 1430°C.
Liquid phase sintering is preferable for better rolling, higher density and healing of cracks which can form during drying. Densities of about 99.4% of theoretical have been achieved in practice. Usually liquid phase sintering results in a more uniform composition of the alloy components throughout the sheet. The liquid phase sintering temperature is above the solidus temperature of the matrix phase of the alloy but below the melting point of tungsten.
The resulting sheet can now be processed by known methods of hot rolling and annealing to form the final size sheet. However, when the process of the present invention is followed to produce a sheet which is close to the desired final thickness, less rolling and annealing are required than with sheets formed by prior art methods. This is because the cake has been formed to a size very close to the desired size of the final sheet.
To more fully illustrate this invention, the following non-limiting example 3 is presented.

Example 3

A mixture of tungsten, nickel, and iron powder in the correct proportions for the alloy having a composition of about 4.9% Ni, about 2.1% Fe, and the balance W is mixed with water to form a slurry. The slurry is poured onto an 8" x 8" x 1/2" (20.3cm x 20.3cm x 12.7cm) filter having a construction as shown in Figure 1 (porous plastic medium) and spread out uniformly with a spatula and doctor blade. Multiple passes are made with the doctor blade across the slurry while tapping the filter to bring entrapped air to the surface of the slurry. The slurry is vibrated perpendicular to the place of the filter with an air vibrator. The final levelling is completed to a uniform thickness with a doctor blade. The volume is evacuated underneath the filter medium for about 5 to 10 minutes to remove excess water from the slurry, forming a planar cake. A sheet of zirconium oxide coated molybdenum is bolted down to the filter frame on top of the cake. The assembly is then inverted so the filter medium is above the cake and the cake is resting on the molybdenum sheet. The filter apparatus is vibrated to release the cake from the filter. The filter apparatus is removed leaving the damp cake on the molybdenum sheet. The cake is dried in a convection oven with no heat for about 24 hours. The cake shrinkage is about 15% in length and width, with the final dimensions being 6 3/16" x 6 3/16" (15.7cm x 15.7cm) and about 26% in thickness with final dimensions being 0.25" (6.3mm) thick. The cake is then liquid phase sintered in a hydrogen atmosphere. The liquid phase sintered cake is ground with an abrasive wheel to remove blisters occurring as a result of release of gases during sintering. The resulting sheet preform is heat treated in hydrogen in preparation for rolling. The sheet is rolled down to about 0.230" (5.84mm) thick in 12 passes. This represents a reduction in height (RIH) of about 22% for the highest point on the sintered piece (0.295") (7.49mm). After this rolling step, the piece measures about 7 1/8" x 5 7/8" x 0.175" (18cm x 14.9cm x 0.44cm) thick. The sheet is annealed and rerolled to about 0.175" (0.44mm) thick (24% RIH). The length is from about 10 1/4" (260mm) to about 12 1/4" (311mm), the width is from about 5 5/8" (142.8mm) to about 6" (152.4mm), and the thickness is about 0.125" (3.17mm).
While there has been shown and described what are at present considered the preferred aspects and embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

1. A process for producing a sheet of tungsten heavy alloy, said process comprising:

(a) forming a slurry comprising at least the metal powder components of the alloy;

(b) removing any liquid from said slurry and forming a planar cake of the solid compounds of said slurry;

(c) thereafter drying the cake; and

(e) sintering the cake to a density equal to or greater than about 90% of the theoretical density of the alloy to form the sheet.

2. A process of claim 1 wherein step (a) comprises a step of uniformly blending elemental metal powder components of said alloy by forminga slurry of said powder components in a liquid medium.

3. A process of claim 2 wherein said liquid medium is selected from the group consisting of water, oxygen containing organic solvents and non-oxygen containing organic solvents.

4. A process of claim 3 wherein said liquid medium is selected from the group consisting of water, and oxygen-containing organic solvents.

5. A process of claim 4 wherein the dried cake before the sintering step is heated in hydrogen at a temperature sufficient to reduce any metal oxides which are present to their respective metals but below the sintering temperature of any metal contained therein.

6. A process of claim 5 wherein said temperature is from about 800°C to about 1000°C.

7. A process of claim 1 comprising:

(a) uniformly blending metal powder components of said alloy by forming a slurry of said powder components, one or more chemical compounds of at least one of said components of said alloy as an inorganic binder, in a liquid medium with said chemical compound being soluble in said liquid medium and capable of being decomposed into one or more of said metal components of said alloy below the melting point of said metal powder components;

(b) removing said liquid medium from said powder components and forming a planar cake of said powder components and said inorganic binder;

(c) drying said cake;

(d) heating said cake in a non-oxidising atmosphere at a temperature sufficient to decompose said inorganic binders into their elemental components or oxides;

(e) heating the resulting first heated cake in a reducing atmosphere at a temperature sufficient to reduce any oxides formed during steps (a), (b), (c), and (d) to the metals;

(f) sintering the resulting reduced cake to a density equal to or greater than about 90% of the theoretical density of said alloy to form said sheet.

8. A process of claim 7 wherein said inorganic binders are selected from the group consisting of ammonium paratungstate and ammonium metatungstate, iron chloride, nickel chloride, iron hydroxide, nickel hydroxide, and iron oxalate and nickel oxalate.

9. A process of claim 7 or 8 wherein said inorganic binders are selected from the group consisting of ammonium paratungstate and ammonium metatungstate.

10. A process of claim 1 comprising

(a) forming a solution of chemical compounds containing metal values of said alloy in the correct proportion as in said alloy;

(b) crystallising said compounds from said solution and drying said compounds;

(c) reducing said compounds to their respective metals wherein each particle is an admixture of the alloy components;

(d) forming a slurry of said metals and liquid medium;

(e) removing said liquid medium from said metals and forming a planar cake of said metals;

(f) drying said cake; and

(g) sintering said cake to a density equal to or greater than about 90% of the theoretical density of said alloy to form said sheet.

11. A process of claim 10 wherein said liquid medium is selected from the group consisting of water, oxygen containing organic solvents and non-oxygen containing organic solvents.

12. A process of claim 11 wherein said liquid medium is selected from the group consisting of water and oxygen-containing organic solvents.

13. A process of claim 12 wherein the dried cake before the sintering step is heated in hydrogen at a temperature sufficient to reduce any metal oxides which are present to their respective metals but below the sintering temperature of any metal contained therein.

14. A process of claim 13 wherein the temperature is from about 800°C to about 1000°C.

15. A process of claim 1 comprising:

(a) forming metal particles of said alloy wherein each metal particle is a uniform admixture of said alloy components;

(b) entraining said particles in a carrier gas to form entrained particles;

(c) passing said entrained particles and said carrier gas into a high temperature zone at a temperature above the melting point of the matrix phase of said particles and maintaining said particles in said zone for a sufficient time to melt at least said matrix phase of said particles and form spherical particles;

(d) rapidly and directly resolidifying the resulting high temperature treated material, whilse said material is in flight;

(e) forming a slurry of said high temperature treated material and a liquid medium;

(f) removing said liquid medium from said high temperature treated material forming a planar cake of said high temperature treated material;

(g) drying said cake; and

(h) sintering said cake to a density equal to or greater than about 90% of the theoretical density of said alloy to form said sheet.

16. A process of claim 15 wherein said mixture is formed by a process which comprises the steps of:

(a) agglomerating said alloy metal powder components with an organic binder to form agglomerates each of which is an admixture of the components of said alloy in the proper proportion as in said alloy;

(b) removing said organic binder from the resulting agglomerated powder components to form dewaxed agglomerates; and

(c) sintering said dewaxed agglomerates to form sintered agglomerates.

17. A process of claim 15 wherein said admixture is formed by a process which comprises the steps of:

(b) crystallising said compounds from said solution and drying said compounds; and

(c) reducing said compounds to their respective metals wherein each particle is an admixture of the alloy components.

18. A process of claim 15 wherein said high temperature is a plasma.

19. A process of claim 15 wherein said liquid medium is selected from the group consisting of water, oxygen containing organic solvents, and non-oxygen containing organic solvents.

20. A process of claim 19 wherein said liquid medium is selected from the group consisting of water and oxygen containing organic solvents.

21. A process of claim 20 wherein the dried cake before the sintering step is heated in hydrogen at a temperature sufficient to reduce any metal oxides which are present to their respective metals but below the sintering temperature of any metal contained therein.

22. A process of claim 21 wherein said temperature is from about 800°C to about 1000°C.

23. A process of claim 1 comprising:

(a) uniformly blending elemental metal powder components of said alloy by forming a slurry of said powder components in a liquid medium;

(b) introducing said slurry onto a filter medium and applying vacuum to the bottom of said slurry to form a planar cake of said powder components;

(c) drying said cake; and

(d) sintering said cake to a density equal to or greater than about 90% of the theoretical density of said alloy to form said sheet.

24. A process of claim 23 wherein said liquid medium is selected from the group consisting of water, oxygen containing organic solvents and non-oxygen containing organic solvents.

25. A process of claim 24 wherein said liquid medium is selected from the group consisting of water and oxygen containing organic solvents.

26. A process of claim 25 wherein the dried cake before the sintering step is heated in hxdrogen at a temperature sufficient to reduce any metal oxides which are present to their respective metals but below the sintering temperature of any metal contained therein.

27. A process of claim 26 wherein said temperature if from about 800°C to about 1000°C.

28. A process of claim 23 wherein said filter medium is vibrated before application of said vacuum.

29. A process of claim 23 wherein said filter medium is vibrated during application of said vacuum.