Claims
- 1. A substantially fully dense compacted and unsintered powdered metal composite, comprising: (a) a metal or metal alloy matrix having uniformly dispersed therein discrete microparticles of a refractory metal oxide and (b) discrete macroparticles of an additive material.
- 2. The composite of claim 1 wherein the additive material is a metal, metal alloy or metal compound having a low thermal expansion coefficient.
- 3. The composite of claim 2 wherein the metal, metal alloy or metal compound is selected from the group consisting of tungsten, molybdenum, niobium, tantalum, rhenium, chromium, tungsten-rhenium, tungsten-nickel-iron, nickel-iron, nickel-iron-cobalt and tungsten-carbide.
- 4. The composite of claim 1 wherein the additive material is a metal, metal alloy or metal compound having high strength.
- 5. The composite of claim 4 wherein the metal, metal alloy or metal compound is selected from the group consisting of tungsten, molybdenum, niobium, tantalum, music wire and high alloy steels.
- 6. The composite of claim 1 wherein the additive material is selected from the group consisting of graphite fibers, silicon whiskers, boron and silicon nitride fibers.
- 7. The composite of claim 1 wherein the additive material is a metal, metal alloy or metal compound having high hardness and high wear and arc erosion resistance.
- 8. The composite of claim 7 wherein the additive metal, metal alloy or metal compound is selected from the group consisting of tungsten, molybdenum, niobium, tantalum, rhenium, chromium, tungsten-rhenium, tungsten-carbide and tungsten-nickel-iron.
- 9. The composite of claim 1 wherein the additive material is a metal, metal alloy or metal compound having magnetic properties.
- 10. The composite of claim 9 wherein the additive metal, metal alloy or metal compound is selected from the group consisting of iron, nickel, cobalt, steels, iron-nickel and cobalt-samarium.
- 11. The composite of claim 1, wherein said components (a) and (b) are substantially nonalloyed.
- 12. The composite of claim 1, wherein said components (a) and (b) are substantially noninterdiffused.
- 13. The composite of claim 1, wherein said matrix is a dispersion strengthened metal having an electrical resistivity below about 8.times.10.sup.-6 ohm-cm.
- 14. The composite of claim 1, wherein said matrix is dispersion strengthened copper.
- 15. The composite of claim 1, wherein said matrix is dispersion strengthened copper, and said refractory metal oxide is aluminum oxide.
- 16. The composite of claim 1, wherein said additive material is a refractory metal, refractory metal alloy, or refractory metal compound selected from the group consisting of tungsten, molybdenum, niobium, tantalum and rhenium.
- 17. A substantially fully dense compacted and unsintered powdered metal composite, comprising: (a) a metal or metal alloy matrix having uniformly dispersed therein discrete microparticles of a refractory metal oxide and (b) discrete macroparticles of a refractory metal, refractory metal alloy or refractory metal compound selected to thereby impart to the composite a controlled coefficient of expansion.
- 18. The composite of claim 17, wherein said components (a) and (b) are substantially nonalloyed.
- 19. The composite of claim 17, wherein said components (a) and (b) are substantially noninterdiffused.
- 20. The composite of claim 17, wherein said matrix is a dispersion strengthened metal having an electrical resistivity below about 8.times.10.sup.-6 ohm-cm.
- 21. A substantially fully dense compacted and unsintered powdered metal composite, comprising: (a) a metal or metal alloy matrix having uniformly dispersed therein discrete microparticles of a refractory metal oxide and (b) discrete macroparticles of a refractory metal, refractory metal alloy or refractory metal compound selected to thereby impart to the composite a high strength.
- 22. The composite of claim 21, wherein said components (a) and (b) are substantially nonalloyed.
- 23. The composite of claim 21, wherein said components (a) and (b) are substantially noninterdiffused.
- 24. The composite of claim 21, wherein said matrix is a dispersion strengthened metal having an electrical resistivity below 8.times.10.sup.-6 ohm-cm.
- 25. The composite of claim 21, wherein said matrix is dispersion strengthened copper.
- 26. The composite of claim 21, wherein said matrix is dispersion strengthened copper, and said refractory metal oxide is aluminum oxide.
- 27. The composite of claim 21, wherein said refractory metal, or at least one element of said refractory metal alloy, or refractory metal compound is selected from the group consisting of tungsten, molybdenum, chromium, niobium, rhenium, tantalum and tungsten-carbide.
- 28. A substantially fully dense compacted and unsintered powdered metal composite, comprising: (a) a metal or metal alloy matrix having uniformly dispersed therein discrete microparticles of a refractory metal oxide and (b) discrete macroparticles of a refractory metal, refractory metal alloy or refractory metal compound selected to thereby impart to the composite a high wear resistance.
- 29. The composite of claim 28, wherein said components (a) and (b) are substantially nonalloyed.
- 30. The composite of claim 28, wherein said components (a) and (b) are substantially noninterdiffused.
- 31. The composite of claim 28, wherein said matrix is a dispersion strengthened metal having an electrical resistivity below 8.times.10.sup.-6 ohm-cm.
- 32. The composite of claim 28, wherein said matrix is dispersion strengthened copper.
- 33. The composite of claim 28, wherein said matrix is dispersion strengthened copper, and said refractory metal oxide is aluminum oxide.
- 34. The composite of claim 28, wherein said refractory metal, or at least one element of said refractory metal alloy, or refractory metal compound is selected from the group consisting of tungsten, molybdenum, and chromium, niobium, rhenium, tantalum and tungsten-carbide.
- 35. A substantially fully dense compacted and unsintered powdered metal composite, comprising: (a) a metal or metal alloy matrix having uniformly dispersed therein discrete microparticles of a refractory metal oxide and (b) discrete macroparticles of a mechanical or physical property-conferring material having mechanical or physical parity with component (a).
- 36. The composite of claim 35, wherein said components (a) and (b) are substantially nonalloyed.
- 37. The composite of claim 35, wherein said components (a) and (b) are substantially noninterdiffused.
- 38. The composite of claim 35, wherein said matrix is a dispersion strengthened metal having an electrical resistivity below 8.times.10.sup.-6 ohm-cm.
- 39. The composite of claim 35, wherein said matrix is dispersion strengthened copper.
- 40. The composite of claim 35, wherein said matrix is dispersion strengthened copper, and said refractory metal oxide is aluminum oxide.
- 41. The composite of claim 35, wherein component (b) is a refractory metal, refractory metal alloy or refractory metal compound.
- 42. The composite of claim 35, wherein said refractory metal, or at least one element of said refractory metal alloy, or at refractory metal compound is selected from the group consisting of tungsten, molybdenum, and chromium.
- 43. A process for forming a substantially fully dense compacted and unsintered powdered metal composite, comprising compacting without sintering: (a) a metal or metal alloy matrix having uniformly dispersed therein discrete microparticles of a refractory metal oxide and (b) discrete macroparticles of a mechanical or physical property-conferring material having mechanical or physical parity with component (a).
- 44. The process of claim 43, wherein said components (a) and (b) are substantially nonalloyed.
- 45. The composite of claim 43, wherein said components (a) and (b) are substantially noninterdiffused.
- 46. The composite of claim 43, wherein said matrix is a dispersion strengthened metal having an electrical resistivity below 8.times.10.sup.-6 ohm-cm.
- 47. The composite of claim 43, wherein said matrix is dispersion strengthened copper.
- 48. The composite of claim 43, wherein said matrix is dispersion strengthened copper, and said refractory metal oxide is aluminum oxide.
- 49. The composite of claim 43, wherein component (b) is a refractory metal, refractory metal alloy or refractory metal compound.
- 50. The composite of claim 43, wherein said refractory metal, or at least one element of said refractory metal alloy, or at refractory metal compound is selected from the group consisting of tungsten, molybdenum, chromium, niobium, rhenium, tantalum and tungsten-carbide.
- 51. The composite of claim 1 wherein the additive material is a superconductor.
- 52. The composite of claim 2 wherein the material is selected from the group consisting of niobium-tin, niobium-titanium and copper-barium-yttrium oxide.
- 53. A substantially fully dense compacted and unsintered powdered metal composite as described in claim 1 wherein component (a) is dispersion strengthened copper and the additive material is niobium.
BACKGROUND OF THE INVENTION AND PRIOR ART
This application is a continuation-in-part of Ser. No. 561,035, filed Dec. 13, 1983, U.S. Pat. No. 4,752,334.
This invention is in the field of powder metallurgy and relates to metal composites in which one of the metallic ingredients is a preformed dispersion strengthened metal, e.g., dispersion strengthened copper, and a second is a different material capable of conferring desired mechanical or physical properties to the composite. The composites of the invention are critically unsintered consolidates produced by processing steps such as pressing, extrusion, swaging or rolling (or combinations thereof), and can take a variety of shapes such as billets, strips, rods, tubes or wires. These composites can be fabricated to have a wide range of mechanical properties including strength, hardness, wear and arc erosion resistance while simultaneously possession useful physical properties including high conductivity, low thermal expansion, magnetic properties etc., heretofore unknown to conventional composite systems.
This invention has for its principal objective the provision of a composite that has relatively good electrical and thermal conductivity, and, for example, a low coefficient of thermal expansion, high hardness, high wear resistance, particular magnetic properties, and/or other properties or characteristics desired. Without limiting the scope of this invention, one way to achieve these objectives is by blending powders and compacting to substantially full density, principally (but not exclusively) by hot isostatic pressing ("HIPing") and/or hot extrusion without sintering, the following two components:
(a) a preformed dispersion strengthened metal provided typically as a powder (before blending with component (b)) and including, e.g., dispersion strengthened copper, silver, or aluminum, desirably having an electrical resistivity below 8.times.10.sup.-6 ohm-cm, and
(b) an additive material consisting for example of metals such as chromium and titanium and alloys of these metals, or refractory metals, alloys and compounds having one or more refractory metals as the major constituent.
"Additive material", as used herein, generally refers to metals, alloys or compounds having one or more desirable physical or mechanical characteristics, including high density, high melting point, low coefficient of expansion, and superior resistance to wear, arc erosion and acid corrosion, and include, but are not limited to molybdenum, tungsten, titanium, niobium, tantalum, rhenium, and chromium as well as alloys such as nickel with iron, nickel with iron and cobalt, iron-nickel alloys containing for example from about 30-55% nickel by weight plus minor additives such as manganese, silicon and carbon, samarium/cobalt, chromium with molybdenum, beryllium-copper, various steels (including maraging, stainless and music wire), and various combinations of two or more suitable alloying metals (including tin, zinc, tin/zinc mixtures, silicon, magnesium, beryllium, zirconium, silver, chromium, iron, nickel, phosphorus, titanium and samarium). Also included are alloys and compounds of refractory metals such as tungsten-rhenium, tungsten-nickel-iron, tungsten-carbide etc. Superconducting materials, for example niobium-tin, niobium-titanium and copper-barium-yttrium oxide can be added to the dispersion strengthened metal (i.e. copper) to form a composite wherein the DSC acts as a stabilizer for the superconducting materials.
Dispersion strengthened metals are well known. Reference may be had to U.S. Pat. No. 3,779,714 to Nadkarni, et al., and the references discussed in the text thereof, all incorporated herein by reference, for examples of dispersion strengthened metals, especially copper, and methods of making dispersion strengthened metals. In Nadkarni, et al., dispersion strengthened copper (hereinafter called "DSC") is produced by forming an alloy of copper as a matrix metal and aluminum as a refractory metal oxide forming, solute metal. This alloy, containing from 0.01% to 5% by weight of the solute metal, is comminuted by atomization (See U.S. Pat. No. 4,170,466), or by conventional size reduction methods to a particle size, desirably less than about 300 microns, preferably from 5 to 100 microns, then mixed with an oxidant. The resultant alloy powder-oxidant mixture is then compacted prior to heat treatment, or heated to a temperature sufficient to decompose the oxidant to yield oxygen which internally oxidizes the solute metal to the solute metal oxide in situ, thereby providing a very fine and uniform dispersion of refractory metal oxide, e.g., alumina, throughout the matrix metal. Thereafter, the preformed dispersion strengthened metal is collected as a powder or submitted to size reduction to yield a powder having a particle size of from -20 mesh to submicron size for use herein. Alternatives, such as mechanical alloying of the matrix and solute metals as by prolonged ball milling of a powder mixture for 40 to 100 hours can also be used prior to internal oxidation.
Dispersion strengthening can be accomplished in a sealed can or container (U.S. Pat. No. 3,884,676). The alloy powder may be recrystallized prior to dispersion strengthening (U.S. Pat. Nos. 3,893,844 and 4,077,816). Other processes are disclosed in U.S. Pat. Nos. 4,274,873; 4,315,770 and 4,315,777 at Col. 6, lines 5-16). The disclosures of all of the foregoing U.S. Patents are incorporated herein by reference; these patents are commonly owned with the present application.
Certain other composites of metal powders seeking low thermal expansion characteristics and low resistivity are known. U.S. Pat. No. 4,158,719 to Frantz discloses a composite made by compacting a mixture of two powders, one of which has low coefficient of thermal expansivity and the other of which has high thermal conductivity. The composite is useful, like the products of the present invention, in the production of lead frames for integrated circuit chips. Frantz's composite is made by mixing the powders, forming into a green compact, and, in distinction from the present invention, sintering and then rolling to size. Frantz discloses a low thermal expansivity alloy containing 45 to 70% iron, 20-55% nickel, up to 25% cobalt and up to 5% chromium, which in powder form is mixed with a high thermal conductivity metal powder of substantially elemental iron, copper, or nickel. However, none of the metals disclosed by Frantz is dispersion strengthened. In addition, the pressing-sintering and rolling to size taught by Frantz does not work with dispersion strengthened copper composite.
U.S. Pat. No. 4,501,941 to Cherry discloses a process for making a vacuum interrupter electrical contact by admixing a copper powder which is dispersed with finely divided aluminum oxide and chromium powders, cold pressing the admixed powders at high pressure to form a compact of high intermediate density, (for example pressing the admixed powders into the required shape in a die at about 60 tons/square inch) and then sintering the compact at a temperature below the melting point of copper (col.3, lines 1-5). Cherry discloses that the additive metal minor portion of the compact is preferably chromium, but refractory metals such as tungsten or tungsten carbide can be utilized. As shown in our comparative examples below however, cold pressing causes laminations. In addition, the strength of sintered compacts is very poor in the case of dispersion strengthened copper composites made by this process. The instant invention overcomes problems of the Cherry processes and products, such as marked laminations (surface cracks) and weaknesses. These imply poor green strength, and render the product unsuited for many uses, such as for example, as an electrical contact material (see comparative examples below).
Critical to the present invention, we have found that not only does the use of dispersion strengthened materials give rise to a stronger, harder product, but, hot isostatically pressing or hot extruding at significantly lower temperatures for example, 1750.degree. F. and 1650.degree. F. respectively, compared to Cherry's temperature of 1920.degree. F., together with the other controlled parameters herein, a product substantially devoid of laminations, while simultaneously possessing improved hardness and higher conductivity, can be formed. The superior strength inhot isostatically pressed material arises from acheiving substantially full density. The sintering step taught by Cherry, at high temperatures such as 1920.degree. F. causes more diffusion of additive metal atoms into copper thus reducing conductivity. The instant invention which uses hot extrusion or hot isostatic pressing keeps the temperature below this temperature reducing such diffusion.
Nickel/iron alloys that contain 36% Ni, balance Fe with Mn, Si and C totalling less than 1%, are known as "Nilvar" or "Alloy 36". Nickel/iron alloys that contain 42% Ni, balance Fe with Mn, Si and C totalling less than 1%, are members of a family of nickel/iron alloys known as "Invar" or "Alloy 42". Nickel/iron alloys that contain 46% Ni, balance Fe with Mn, Si and C totalling less than 1%, are known as "Alloy 46". Similarly, "Alloys 50" and "52" comprise 50% Ni and 52% Ni, respectively, with the balance being substantially Fe.
The respective properties of the sintered composites of the prior art and the unsintered composites of the present invention have been studied, and one of the improvements of the instant invention (a composite having both high hardness and high conductivity) is thereby made apparent. Other characteristics can be obtained in a composite by following the teachings herein without deviating from the spirit of the invention.
A composite strip and wire were made with DSC and copper and each of (1) 36% Ni/64% Fe (Nilvar) and (2) 42% Ni/58% Fe (Invar) and the respective procedures were followed for forming the composites. Those composites made with DSC and the Invar alloys have high strength and good strength retention after exposure to high temperatures. The prior art material iron with Nilvar, alloy (1), and iron with Invar, alloy (2), show higher strength than copper metal with alloys (1) or (2), but this is only with the sacrifice of electrical conductivity.
To obtain high strength with copper composites, the prior art has had to use fine powder which reduces conductivity significantly. On the other hand, coarse copper powder yields high conductivity but lower strength.
Another example of the prior art, U.S. Pat. No. 4,366,065 to Bergmann, et al., discloses the preparation of a composite material by powder metallurgy wherein a starting material (comprised of at least one body-centered cubic metal contaminated by oxygen in its bulk and on its surface) is mixed with a less noble supplemental component that has a greater binding enthalpy for oxygen in powder form, or as an alloy whereby the oxygen contaminant becomes bound to the supplemental component (aluminum) by internal solid state reduction. The composite is then deformed in at least one dimension to form ribbons or fibers thereof. Niobium-copper is exemplified with aluminum as the oxygen getter.
A principal advantage of using DSC as opposed to using plain copper (like Bergmann, et al.) appears to be that DSC enables closer matching of stresses required for deformation of the two major components. Because of closer matching, the powder blends and composites can be co-extruded, hot forged, cold or hot rolled and cold or hot swaged. When one of the components undergoing such working is excessively harder, for example, than the other, then the particles of the harder component remain undeformed. The flow of softer material over and around the harder particles generally leads t the formation of voids and cracks, and hence weakness in the structure. The greater strength of the DSC material over the unmodified or plain copper enables closer matching with the additive metal as, for example, with respect to yield strength, and the size and shape of the regions occupied by the individual components will be more nearly alike. Closer matching of forming stresses enables achievement of full density for the powder blend in one hot forming operation, such as extrusion, or multiple size reduction steps such as swaging or rolling. This, we have found, eliminates much of the need for sintering.
The prior art universally utilizes sintering (typically two steps) at very high temperatures (1850.degree. F. for copper and 2300.degree. F. for iron or 1920.degree. F., as in Cherry). These temperatures promote inter-diffusion of atoms of the two components or alloying to occur, which we have found to be disadvantageous to the desired characteristics of the composite. Diffusion of iron and/or nickel or other metals into copper lowers the electrical conductivity of the copper and conversely, diffusion of copper into the additive metal adversely effects its coefficient of thermal expansion. The prior art is devoid of effective solutions: to obtain a composite with both high hardness and high conductivity.
In carrying out the present invention the temperatures utilized are below sintering temperature used in prior art procedures and, we have found that, as a result, inter-diffusion of atoms, or alloying, between the principal components is reduced. From the prior art it can be seen that when sintering time is increased from 3 minutes to 60 minutes, the electrical resistivity actually increases significantly from 35 up to 98 microhm-cm. (See examples 4 and 6 and examples 5 and 7 in U.S. Pat. No. 4,158,719). Stated in another way, electrical conductivity, the goal, decreases significantly. This variation in resistivity or conductivity, believed to be due to interdiffusion of copper and nickel (for example, from Invar alloy 42), is a serious problem. Use of DSC instead of copper or a copper alloy, while controlling the temperature below sintering, retards such inter-diffusion because the dispersed refractory oxide, e.g., Al.sub.2 O.sub.3 acts as a barrier to or inhibitor of diffusion. DSC (AL 15) has an electrical conductivity of 90-92% IACS and an annealed yield strength of 50,000 psi.
Other patent references of interest, yet distinguishable from the instant invention, include U.S. Pat. No. 2,853,401 to Mackiw, et al. which discloses chemically precipitating a D.S. metal onto the surface of fine particles of a carbide, boride, nitride or silicide of a refractory hard metal to form a composite powder and then compacting the powder. U.S. Pat. No. 4,032,301 to Hassler discloses a contact material for vacuum switches formed of mixed powders of a high electrical conductivity metal, e.g., copper, and a high melting point metal, e.g., chromium, compacted, that are then sintered. U.S. Pat. No. 4,139,378 to Bantowski is concerned with brass powder and compacts improved by including a minor amount of cobalt. The compacts are sintered. U.S. Pat. No. 4,198,234 Cadle et al. discloses mixing a pre-alloy powder of chromium, iron, silicon, boron, carbon and nickel at least about 60%, and copper powder, compacting the blend and liquid phase sintering at 1920.degree. F. to 2010.degree. F. to partly dissolve the copper and nickel alloy in one another.
The present invention is distinguished from the prior art particularly in that the unsintered composite product is made by compacting a preformed dispersion strengthened metal, e.g., DSC, dispersion strengthened aluminum or dispersion strengthened silver, together with an additive metal, alloy and/or compound. The product of this invention, in addition to having relatively high electrical conductivity, has improved mechanical properties not possessed by the prior art composites, because we have found the materials are critically compacted to substantially full density without a sintering step.
Briefly stated, the present invention is in a substantially fully dense composite comprising a metal matrix having dispersed therein discrete microparticles of a refractory metal oxide and macroparticles of an additive material such as a different metal or metal alloy, a refractory metal, refractory metal alloy or refractory metal compound.
The products hereof are characterized by good electrical and thermal conductivity plus another mechanical or physical property characteristic of the additive metal or metal alloy, for example, a low coefficient of thermal expansion. Those products having low coefficient of thermal expansion are especially useful in fabricating lead frames for semiconductors and integrated circuits, as well as in lead wires in electric lamps. Other composites include those characterized by high strength, high wear and arc erosion resistance or magnetic properties. The invention also contemplates a method for producing such composites characterized by densifying a blend of (a) a dispersion strengthened metal powder and (b) a powdered refractory metal, alloy, or compound at a temperature low enough to minimize alloying and interdiffusion between (a) and (b).
US Referenced Citations (1)
| Number |
Name |
Date |
Kind |
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4752334 |
Nadkarni et al. |
Jun 1988 |
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Continuation in Parts (1)
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Number |
Date |
Country |
| Parent |
561035 |
Dec 1983 |
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Patent Grant
4999336
