USH1146H - Plasma spraying tungsten heavy alloys - Google Patents
Plasma spraying tungsten heavy alloys Download PDFInfo
- Publication number
- USH1146H USH1146H US07/709,909 US70990991A USH1146H US H1146 H USH1146 H US H1146H US 70990991 A US70990991 A US 70990991A US H1146 H USH1146 H US H1146H
- Authority
- US
- United States
- Prior art keywords
- tungsten
- alloy
- powdered
- alloys
- full density
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/045—Alloys based on refractory metals
Definitions
- the invention relates to heavy alloys of tungsten and methods of producing such alloys.
- Tungsten heavy alloys which are of great value in counter weights for aircraft, in ballistics, and in other applications, are conventionally produced by liquid phase sintering of mixed elemental powders. Alloys produced by this method are generally two-phase composites consisting of rounded tungsten grains dispersed in an alloy matrix.
- tungsten heavy alloys are strongly dependent upon their specific microstructural features: for example, the grain size, contiguity, dihedral angle and the volume fraction of the tungsten phase.
- the optimal microstructure exhibits low contiguity, small grain size, and strong W-W grain boundary and W-matrix interface.
- Solid state sintering is a known means for obtaining finer alloy microstructures.
- the microstructure of solid state sintered heavy alloys using tungsten powder of spherical morphology exhibit low contiguity and finer grain size in comparison with materials produced by liquid phase sintering.
- the mechanical properties of these solid state-produced materials, especially their ductility, is very low.
- the probable cause of low ductilities in these materials is the weak interphase and interface boundaries of their composite microstructure.
- Still another object of the present invention is to provide methods for producing and fabricating tungsten heavy alloys exhibiting the properties described hereinabove.
- the present invention resides, briefly stated, in the use of plasma rapid solidification technology to fabricate improved tungsten/tungsten alloys of spherical morphology.
- the composition of the alloys by weight is based on the following generic formula:
- the alloys are produced by introducing elemental or alloy powders into a thermal spray plasma gun, melting the powders in the hot zone of the gun and then spraying the molten material into a collecting chamber where they are cooled by the gas in the chamber, whereupon the resulting powder is collected.
- the phase "tungsten heavy alloys” refers to alloys of tungsten which have a density greater than 15 g/cc.
- well-mixed metallic powder comprising from about 80 to about 100% by weight tungsten and from about 0 to about 20% by weight of at least one alloying metal selected from the group consisting of molybdenum, tantalum, niobium, hafnium, rhenium, and chromium is fed by internal or external feed into a thermal spray plasma gun, for example, a Baystate Model PG-100 plasma gun (Baystate Co., Westboro, Mass.). That gun has a power rating of 28 kilowatts and an internal feed nozzle.
- the ionized gas plume in a thermal spray plasma gun can reach temperatures of 10,000° Kelvin and is particularly suitable for melting tungsten, which has the highest melting point of any metal (3410° C.).
- the mixed metallic powder is passed rapidly through the gas plume of the plasma gun, which plume may comprise ionized inert gases, such as argon, together with a small amount of helium or hydrogen.
- the powder melts almost instantaneously in the extremely hot gas plume, becoming a stream of molten metal alloy droplets.
- the molten alloy is then sprayed in droplet form into a collecting chamber having an atmosphere composed of one or more relatively cool, inert gases, for example, argon, helium or nitrogen.
- the temperature of the atmosphere in the chamber is preferably ambient or near-ambient, but may be any temperature low enough to cause rapid solidification of the metal droplets.
- the molten alloy droplets solidify or "freeze" into tungsten alloy powder granules in the collecting chamber, and the powder is collected.
- the resultant powder has an average grain size of from about 5 to about 30 ⁇ m, and preferably from about 15 to about 25 ⁇ m.
- the tungsten alloy powders are further treated in a heated hydrogen-containing atmosphere, preferably at about 600°-900° C., to thoroughly clean and reduce any surface oxides.
- the clean alloy powders can then be intermixed with elemental or alloy powders of at least one metal selected from the group consisting of copper, iron, nickel, cobalt and tantalum in a weight ratio of from about 90 to about 100% tungsten alloy powder and from about 0 to about 10% of the other metal powders.
- the intermixed powder may be compacted by dynamic or explosive compaction to form near fully density metallic compacts.
- Dynamic or explosive compaction produces a very small amount of incipient melting around the tungsten particles for a very short time. The presence of this liquid strongly improves the interface strength, but since the quality of the melt and the time period is extremely small, any measurable grain growth of tungsten is prevented.
- the near full density compact can be further thermomechanically processed by, for example, extrusion, swaging or rolling to improve the properties of the material.
- the fully dense tungsten heavy alloy materials produced according to the foregoing process exhibit a fine-grained microstructure, low contiguity and improved interface strength and ductility in comparison with prior art materials.
- the novel tungsten heavy alloys are extremely valuable for kinetic energy penetrator applications, and may substantially improve the performance of kinetic energy warheads.
- compositions and methods which achieve the various objects of the invention and which are well adapted to meet the conditions of practical use.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Powder Metallurgy (AREA)
- Manufacture Of Metal Powder And Suspensions Thereof (AREA)
Abstract
Tungsten heavy alloys comprising by weight from about 80 to about 100% tuten and from about 0 to about 20% of one or more heavy alloying metals are produced by introducing powders of tungsten and the alloying metals into a thermal spray plasma gun, melting the powders in the hot zone of the gun to form a molten alloy and then spraying the molten alloy in droplet form into a collecting chamber where the droplets are solidified, and the resultant alloy in powdered form is collected. The powdered alloy can be further mixed with powdered copper, iron, nickel, cobalt or tantalum and compacted by dynamic or explosive compaction to form a near full density material. Full density materials are produced by further thermomechanical processing of the compact.
Description
This application is a division of application Ser. No. 07/542,570, filed Jun. 22, 1990, now abandoned.
1. Field of the Invention
The invention relates to heavy alloys of tungsten and methods of producing such alloys.
2. Description of the Prior Art
Tungsten heavy alloys, which are of great value in counter weights for aircraft, in ballistics, and in other applications, are conventionally produced by liquid phase sintering of mixed elemental powders. Alloys produced by this method are generally two-phase composites consisting of rounded tungsten grains dispersed in an alloy matrix.
The mechanical properties of tungsten heavy alloys are strongly dependent upon their specific microstructural features: for example, the grain size, contiguity, dihedral angle and the volume fraction of the tungsten phase. For a given tungsten content, the optimal microstructure exhibits low contiguity, small grain size, and strong W-W grain boundary and W-matrix interface.
There are serious drawbacks associated with the fabrication of tungsten heavy alloys by liquid phase sintering, one of the principal problems being that such alloys almost always exhibit excessive grain growth.
Solid state sintering is a known means for obtaining finer alloy microstructures. In fact, the microstructure of solid state sintered heavy alloys using tungsten powder of spherical morphology exhibit low contiguity and finer grain size in comparison with materials produced by liquid phase sintering. However, the mechanical properties of these solid state-produced materials, especially their ductility, is very low. The probable cause of low ductilities in these materials is the weak interphase and interface boundaries of their composite microstructure.
Improved tungsten heavy alloys and improved methods for producing the same are required.
1. Objects of the Invention
It is an object of the present invention to provide tungsten heavy alloys with improved microstructural features and mechanical properties in comparison with prior at alloys.
It is another object of the present invention to provide such alloys with fine grain size, low contiguity, strong W-W grain boundary and W-matrix interface.
It is a further object of the present invention to provide tungsten heavy alloys with higher strength and ductility than solid state-processed materials.
Still another object of the present invention is to provide methods for producing and fabricating tungsten heavy alloys exhibiting the properties described hereinabove.
2. Brief Description of the Invention
In keeping with the foregoing objects and others which will become hereinafter, the present invention resides, briefly stated, in the use of plasma rapid solidification technology to fabricate improved tungsten/tungsten alloys of spherical morphology. The composition of the alloys by weight is based on the following generic formula:
W.sub.100-x -(Mo, Ta, Nb, Hf, Re, Cr).sub.x
where X=0-20 Wt. %
The alloys are produced by introducing elemental or alloy powders into a thermal spray plasma gun, melting the powders in the hot zone of the gun and then spraying the molten material into a collecting chamber where they are cooled by the gas in the chamber, whereupon the resulting powder is collected.
As used herein, the phase "tungsten heavy alloys" refers to alloys of tungsten which have a density greater than 15 g/cc. To produce the novel tungsten heavy alloys, well-mixed metallic powder comprising from about 80 to about 100% by weight tungsten and from about 0 to about 20% by weight of at least one alloying metal selected from the group consisting of molybdenum, tantalum, niobium, hafnium, rhenium, and chromium is fed by internal or external feed into a thermal spray plasma gun, for example, a Baystate Model PG-100 plasma gun (Baystate Co., Westboro, Mass.). That gun has a power rating of 28 kilowatts and an internal feed nozzle.
The ionized gas plume in a thermal spray plasma gun can reach temperatures of 10,000° Kelvin and is particularly suitable for melting tungsten, which has the highest melting point of any metal (3410° C.).
The mixed metallic powder is passed rapidly through the gas plume of the plasma gun, which plume may comprise ionized inert gases, such as argon, together with a small amount of helium or hydrogen. The powder melts almost instantaneously in the extremely hot gas plume, becoming a stream of molten metal alloy droplets.
The molten alloy is then sprayed in droplet form into a collecting chamber having an atmosphere composed of one or more relatively cool, inert gases, for example, argon, helium or nitrogen. The temperature of the atmosphere in the chamber is preferably ambient or near-ambient, but may be any temperature low enough to cause rapid solidification of the metal droplets. The molten alloy droplets solidify or "freeze" into tungsten alloy powder granules in the collecting chamber, and the powder is collected. The resultant powder has an average grain size of from about 5 to about 30 μm, and preferably from about 15 to about 25 μm.
The tungsten alloy powders are further treated in a heated hydrogen-containing atmosphere, preferably at about 600°-900° C., to thoroughly clean and reduce any surface oxides. The clean alloy powders can then be intermixed with elemental or alloy powders of at least one metal selected from the group consisting of copper, iron, nickel, cobalt and tantalum in a weight ratio of from about 90 to about 100% tungsten alloy powder and from about 0 to about 10% of the other metal powders.
The intermixed powder may be compacted by dynamic or explosive compaction to form near fully density metallic compacts. Dynamic or explosive compaction produces a very small amount of incipient melting around the tungsten particles for a very short time. The presence of this liquid strongly improves the interface strength, but since the quality of the melt and the time period is extremely small, any measurable grain growth of tungsten is prevented.
The near full density compact can be further thermomechanically processed by, for example, extrusion, swaging or rolling to improve the properties of the material.
The fully dense tungsten heavy alloy materials produced according to the foregoing process exhibit a fine-grained microstructure, low contiguity and improved interface strength and ductility in comparison with prior art materials. The novel tungsten heavy alloys are extremely valuable for kinetic energy penetrator applications, and may substantially improve the performance of kinetic energy warheads.
It has thus been shown that there are provided compositions and methods which achieve the various objects of the invention and which are well adapted to meet the conditions of practical use.
As various possible embodiments might be made of the above invention, and as various changes might be made in the embodiments set forth above, it is to be understood that all matters herein described are to be interpreted as illustrative and not in a limiting sense.
Claims (3)
1. A process for producing tungsten heavy alloys of at least 80% by weight of tungsten, said process comprising the steps of:
mixing powder of tungsten and alloying metals in the proportion of at least 80% tungsten by weight and introducing such mixture into a thermal spray plasma gun hot zone;
heating such mixture in the hot zone to form a molten alloy;
spraying such molten alloy in droplet form into a collecting chamber;
cooling such droplets in said chamber to solidify such droplets, which form a tungsten alloy in powdered form.
2. A process as in claim 1 wherein said powdered form tungsten alloy is further processed into an essentially full density material by mixing such tungsten alloy powder with further powdered copper and compacting such mixture by dynamic compaction to form such full density material.
3. A process as in claim 2 wherein a metal chosen from the group of iron, nickel, cobalt, or tantalum is used in place of said copper.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US07/709,909 USH1146H (en) | 1990-06-22 | 1991-05-30 | Plasma spraying tungsten heavy alloys |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US54257090A | 1990-06-22 | 1990-06-22 | |
US07/709,909 USH1146H (en) | 1990-06-22 | 1991-05-30 | Plasma spraying tungsten heavy alloys |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US54257090A Division | 1990-06-22 | 1990-06-22 |
Publications (1)
Publication Number | Publication Date |
---|---|
USH1146H true USH1146H (en) | 1993-03-02 |
Family
ID=27067074
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US07/709,909 Abandoned USH1146H (en) | 1990-06-22 | 1991-05-30 | Plasma spraying tungsten heavy alloys |
Country Status (1)
Country | Link |
---|---|
US (1) | USH1146H (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5956558A (en) * | 1996-04-30 | 1999-09-21 | Agency For Defense Development | Fabrication method for tungsten heavy alloy |
US6635101B2 (en) | 2000-09-01 | 2003-10-21 | Fry's Metals, Inc. | Rapid surface cooling of solder droplets by flash evaporation |
US6746782B2 (en) * | 2001-06-11 | 2004-06-08 | General Electric Company | Diffusion barrier coatings, and related articles and processes |
US6960319B1 (en) * | 1995-10-27 | 2005-11-01 | The United States Of America As Represented By The Secretary Of The Army | Tungsten alloys for penetrator application and method of making the same |
-
1991
- 1991-05-30 US US07/709,909 patent/USH1146H/en not_active Abandoned
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6960319B1 (en) * | 1995-10-27 | 2005-11-01 | The United States Of America As Represented By The Secretary Of The Army | Tungsten alloys for penetrator application and method of making the same |
US5956558A (en) * | 1996-04-30 | 1999-09-21 | Agency For Defense Development | Fabrication method for tungsten heavy alloy |
US6635101B2 (en) | 2000-09-01 | 2003-10-21 | Fry's Metals, Inc. | Rapid surface cooling of solder droplets by flash evaporation |
US6746782B2 (en) * | 2001-06-11 | 2004-06-08 | General Electric Company | Diffusion barrier coatings, and related articles and processes |
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