US 3623860 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
United States Patent 3,623,860 TUNGSTEN-RHENIUM ALLOY POWDER Richard F. Cheney, Harry D. Martin, and Donald S. Parsons, Towanda, Pa., assignors to GTE Sylvania Incorporated No Drawing. Filed Jan. 6, 1969, Ser. No. 789,363 Int. Cl. B22f 9/00; C22b 57/00 US. Cl. 75-.5 AB 5 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to tungsten-rhenium alloys. More particularly it relates to tungsten-rhenium alloy powders having extremely small particle sizes and having a homogeneous tungsten and rhenium distribution throughout the particles and further relates to processes for producing these homogeneous tungsten-rhenium powders.
Heretofore, tungsten-rhenium alloy powders were prepared by mechanically blending tungsten powder and rhenium powder in a preselected ratio of tungsten to rhenium. While the composite powder had the correct ratio, for example 95% tungsten and 5% rhenium, the individual particles were either tungsten or rhenium. In general, the alloys produced from such particles can only be made homogeneous by prolonged sintering and holding the material at elevated temperatures. As can be appreciated, the uniformity of the resulting alloys is dependent to a large degree upon the uniformity of the blending of the two powders. Another method used to make powders that are subsequently processed to form tungsten-rhenium alloys is to deposit rhenium in form of a vapor onto tungsten powder. In most instances, the rhenium is more evenly distributed throughout the tungsten than when mechanical blending is used because most of the particles of tungsten contain some rhenium. However, the homogeneity of the alloy is dependent upon the diffusion of rhenium into the particle of tungsten. The time required to achieve adequate diffusion during the sintering step can be excessive. Alloys having homogeneously distributed low concentrations of either tungsten or rhenium are believed to be unachievable by either of the beforementioned prior art methods. Additionally, 'both processes use conventional tungsten powders, hence the typical particle sizes of the powder are from about 4 to about 6 microns (Fisher Sub-Sieve Size). The time required for the sintering step of the alloy is longer than would be required if the size of the powder particles were smaller. It is be lieved, therefore, that a powder having a homogeneous distribution of tungsten and rhenium throughout each particle, regardless of the small amount of tungsten and rhenium present and that has a smaller particle size thus reducing the sintering time and improving the uniformity of the alloys, would be an advancement in the art.
SUMMARY OF THE INVENTION In accordance with one aspect of this invention, there is provided a tungsten-rhenium alloy powder having an average particle size of from about 0.5 to about 4 microns (as measured by Fisher Sub-Sieve Size) and having a homogeneous distribution of tungsten and rhenium throughout each particle. The powder is capable of being processed to the final alloy by conventional powder metallurgy techniques in substantially less time than was required by the prior art processes. In accordance with another aspect of this invention there is provided a method for producing said powders, said method comprising (a) forming an aqueous solution comprising water, a watersoluble tungsten source, and a water-soluble rhenium source, (b) spray drying the aqueous solution to form tungsten-rhenium alloy powder having the rhenium and tungsten sources relatively homogeneously distributed throughout each particle and (c) heat treating the alloy powder under controlled atmospheric and temperature conditions for a time sufficient to convert said tungsten and rhenium sources to metallic tungsten and rhenium without an appreciable loss of rhenium.
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.
DESCRIPTION OF THE PREFERRED EMBODIMENTS As previously mentioned, in the practice of this invention, tungsten and rhenium are relatively homogeneously distributed within each individual particle of the powder and the particles of the powder are relatively small, thereby enabling a more rapid sintering of the pow ders to form a homogeneous alloy when compared with the prior art processes. By relatively homogeneous it is meant that the percent of tungsten and rhenium in each particle varies less than about :10% by weight from the amount of tungsten and rhenium in the total composition. In most instances it is believed that the variation is appreciably less than 10%. For example, if a 20:80 rhenium to tungsten alloy is desired, the range in each particle would not vary more than from about 12:88 to about 28:72. Electron-micrographs of particles indicate that the particles are completely alloyed, that is, the powder consists of particles that are combined of tungsten and rhenium. X-ray diffraction data also indicate the absence of separate lines for tungsten and for rhenium.
Any water-soluble tungsten source can be used, however, it is preferred to use water-soluble tungsten containing material that can be converted to tungstic oxide under atmospheric conditions at relatively low temperatures, that is below about 300 C. Suitable tungsten sources include ammonium tungstate and ammonium metatungstate.
Any water-soluble rhenium source can be used. As used herein, water-soluble means that at least 0.1 gram of the material will dissolve in cc. of water at 25 C. Suitable rhenium sources include ammonium perrhenate, rhenium trichloride, rhenium hexafiuoride and the like.
Materials with a relatively high water solubility are preferred since the aqueous solution containing the tungsten and rhenium is subsequently dried, thus the smallest amount of water that can be employed and still dissolve the appropriate amounts of tungsten and rhenium is desired in order to minimize drying costs.
After the aqueous solution containing the tungsten and rhenium sources is prepared, the solution is spray dried to form the solid particles. Since the solution containing the tungsten and rhenium sources is a homogeneous solution, the solid particles formed from that solution are also homogeneous.
Conventional spray drying techniques can be used, however, since rhenium oxide can be formed during drying, the temperature of the dried material should not exceed about 300 C. to avoid rhenium loss. In most instances, therefore, the heating medium used to achieve spray drying should not exceed 300 C. by an appreciable amount. As can be appreciated, the foregoing temperature limitations are under atmospheric pressure conditions. Increased or decreased pressure conditions during the drying step can raise or lower the foregoing maximum temperature.
Some rhenium oxides are relatively volatile, however, the rhenium and tungsten sources must be reduced to the metallic form without an appreciable loss of rhenium. Several methods can be used to achieve the reduction without an appreciable rhenium loss. One method is to preheat the powder in air at about 300 C, for about 2 hours and thereafter the powder is heated at higher temperatures under a hydrogen atmosphere as in a conventional tungsten oxide reduction process. If desired, however, the particles immediately after spray drying can be heated in a hydrogen atmosphere at about 400 C. for about two hours. The volatile rhenium oxide does not form under these conditions and the powder can then subsequently be heated in a hydrogen atmosphere at a temperature between about 800 C. and about ll C. to complete the reduction.
Powders containing tungsten and rhenium having essentially any ratio of tungsten to rhenium can be produced. As previously mentioned, the process of this invention is particularly advantageous when relatively small amounts of tungsten or rhenium are desired in the alloy. It is particularly desirable to use the process when alloys having a tungsten to rhenium weight ratio of greater than 95:5 and less than :95 are produced. In most instances, tungsten base alloys with the smaller amounts of rhenium will be preferred.
Because the homogeneity of the alloys produced from the powders of this invention is improved, the properties of the alloys are also improved. For example, the duetility and bend strength of alloys are improved with improved homogeneity of the alloy.
To more fully illustrate some of the advantages of this invention, the following non-limiting detailed example is presented. All parts, proportions and percentages are by weight unless otherwise indicated.
EXAMPLE I About 27 parts of ammonium tungstate and about 1 part of ammonium perrhenate are dissolved in about 83 parts of water. The slurry is fed to a conventional spray tower and dried with air having a temperature of below about 300 C. The dried powder is screened to remove lumps and a sample of the powder after screening has a particle size of from about 0.5 to about 2 microns (FSSS).
The powder is heated to about 300 C. for about 2 hours and no appreciable loss of rhenium is noted. The material is then heated to about ll00 C. in a hydrogen atmosphere for about 5 hours. The powder is then subjected to a wash of hydrochloric acid and hydrofluoric acid to remove any unconverted rhenium or tungsten compounds. Electron-micrographs of samples of the washed metal powder indicate completely alloyed particles, that is, separate crystals of tungsten and rhenium are undetected. Electromicrographs of sample of tungstenrhenium alloy powder produced by the rhenium vapor deposition method clearly show separate tungsten and rhenium crystals. Xray diffraction data of the washed powder do not show strong patterns for tungsten and rhenium whereas X-ray patterns for the material produced by the vapor deposition techniques indicate strong tungsten and rhenium patterns.
Substantially similar results are achieved when the powder after spray drying is pre-reduced in hydrogen at about 400 C. for about 2 hours prior to heating to 1100 C. for about 5 hours in a hydrogen atmosphere to complete the reduction. Additionally, the spray dried powder can be subjected to temperatures of 800 C. and ll00 C. in a hydrogen atmosphere without a loss of rhenium and without any appreciable change in product quality.
After the reduction is complete, the powder can be subjected to standard powder metallurgical techniques for the production of tungsten products. A high quality alloy is thus produced that exhibits improved properties of duetility and bend strength than tungsten-rhenium alloys having essentially the same elemental analysis but produced by either the blending technique or the vapor deposition technique.
While there have been shown and described what is at present considered the preferred 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.
1. A process for producing a homogeneous tungstenrhenium powder suitable for powder metallurgy, said method comprising:
(a) forming an aqueous solution comprising water, a water-soluble tungsten source and a water-soluble rhenium source;
(b) spray drying said aqueous solution to form a tungsten-rhenium alloy powder having the rhenium and tungsten relatively homogeneously distributed throughout each particle, and
(c) heat treating said alloy powder under controlled atmospheric and temperature conditions for a time sufficient to convert said tungsten and rhenium sources to metallic tungsten and rhenium without an appreciable loss of rhenium.
2. A process according to claim 1 wherein the weight ratio of tungsten to rhenium in the final product is less than 5:95.
3. -A process according to claim 1 wherein the weight ratio of tungsten to rhenium is greater than 9515.
4. A process according to claim 1 wherein said alloy powder is heated to about 300 C. for about 2 hours and thereafter is heated to about ll00 C. in a hydrogen atmosphere for about 5 hours.
5. A process according to claim 1 wherein said alloy powder is heated to a temperature of from about 800 C. to about 1100 C. and in a hydrogen atmosphere.
References Cited UNITED STATES PATENTS L. DEWAYNE 'RUTLEDGE, Primary Examiner W. W. STALLARD, Assistant Examiner US. Cl. X.R. 84
"UNETED STATES PATE NT OFFECE CER'HFICATE @F CGREflilON Patent No. 3,623,860 Dated November 30, 1971 inventor) Richard F. Cheney, Harry D. Martin, Donald S. Parsons It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Col. 1, line 64 in the Specification "small amount" delete "small" Signed and sealed this 23rd day of May 1972.
EDWARD T-I.FL1TCEEH,JR. ROBERT GOTTSCHALK Attesti'ng Officer Commissionerof Patents