US3399981A - Tungsten-rhenium alloys - Google Patents

Description

zs m GR 393999981 5R Sept 1968 D. J. MAYKUTH ETAL 3,399,981

TUNGSTEN-RHENIUM ALLOYS Filed April 25, 1967 7 Sheets-Sheet 1 FIG. 2

ATTO R N EY P 3, 1968 D. J. MAYKUTH ETAL 3,399,981

' TUNGSTENQRHENIUM ALLOYS Filed April 25. 1967 'T'Sheets-Sheet 2 INVENTORS DANIEL J. MAYKUTH ELMO P. BERGERON JOHN H. PEARSON BY A X ATTORNEY Sept. 3, 1968 D. J. MAYKUTH ETAL TUNGSTEN-RHENIUM ALLOYS 7 Sheets-Sheet 5 Filed A ril 25, 1967 FIG. /2

FIG 1/ INVENTORS DANIEL J. MAYKUTH ELMO P. BERGERON JOHN H, PEARSON ZQWLML if ATTORNB? D. J. MAYKUTH ETAL 3,399,981

TUNG STEN-RHENIUM ALLOYS '7 Shets-Sheet 4 Sept. 3, 1968 Filed April 25, 1967 INVENTORS DANIEL J. IVIAYKUTH ELMO P. BERGERON J OHN H. PEARSON ATTORNEY Sept. 3, 1968 D. J. MAYKUTH ETAL TUNGSTEN RHEN IUM ALLOYS Filed April 25, 1967 7 Sheets-Sheet 5 FIG. /X

INVENTORS DANIEL J. MAYKUTH ELMO P. BERGERON JOHN H. PEARSON BY ATTORNEY: AAK

P 1968 D. J. MAYKUTH ETAL 3,399,981

TUNGSTEN-RHENIUM ALLOYS 7 Sheets-Sheet 6 Filed April 25, 1967 RHENIUM CONTENT, PERCENT BY WEIGHT FIG. 23

INVENTORS. DANIEL J. MAYKUTH ELMO P. BERGERON JOHN H. PEARSON ATTORNEY pt. 3, 1968 D. .1. MAYKUTH ETALO 3,399,981

TUNGSTEN-RHENIUM ALLOYS Filed April 25, 1967 7 Sheets-Sheet 7 SEED PARTICLES SAFETY VENT I/ L EXHAUST GASES REACTOR 3) REDUCTION\ 51 2 1 ZONEW :27:

HEATER MEANS (l2) PURIFIED INERT GAS OR HYDROGEN PURIFIED HYDROGEN TUNGSTEN HEXAFLUORIDE 2% RHENIUM HEXAFLUORIDE PAR'HCLES INVENTORS DANIEL J. MAYKUTH ELMO P. BERGERON JOHN H. PEARSON United States Patent 3,399,981 TUNGSTEN-RHENIUM ALLOYS Daniel J. Maykuth, Columbus, Ohio, Elmo P. Bergeron, Baton Rouge, La., and John H. Pearson, Glen'Rock, N.J., assignors to Allied Chemical Corporation, New York, N.Y., a corporation of New York Filed Apr. 25, 1967, Ser. No. 634,434 Claims. (Cl. 29182.2)

ABSTRACT OF THE DISCLOSURE Alloys of tungsten and rhenium in the form of particles having a microstructure consisting essentially of from 0.5 to 25.0% by weight of rhenium are prepared by vapor phase reduction of tungsten hexafluoride and rhenium hexafluoride. The alloys may be worked into products useful, e.g., in rocket components.

BACKGROUND OF INVENTION Tungsten-rhenium alloys prepared by vacuum-consumable-arc or electron beam melting of pressed and sintered electrodes of tungsten and rhenium powders orother powder metallurgical processes have beenre'portedin the literature. However, these tungsten-rhenium alloy-s generally fail to retain acceptable bend and low-temperature tensile ductility when subjected to ahigh temperature experience, thereby rendering them unsuitable in various high temperature applications. Further, the prior art tungsten-rhenium alloys which exhibit a bend transition temperature approximating that of the present alloys after a high temperature experience require a high rhenium content as compared with the alloys of the present invention, thereby rendering the prior art alloys impractical in view of their high cost.

In U.S.P. 3,234,007, issued Feb. 8, 1966, a novel tungsten particulate product produced by reduction of tungsten hexafluoride is described. The'unalloyed tungsten product prepared by this process exhibits outstanding strength and ductility as compared with other forms of commercially available tungsten. In'addition, significant metallurgical and mechanical property advantages displayed by the novel tungsten metal of U.S.P 3,234,007 in its particulate form are retained in consolidated and metallurgically worked forms produced therefrom. For

example, the fine-grain microstructure of the particles is retained substantially unimpaired throughout consolidation and working of the new tungsten particles and their discrete, consolidated and wrought forms exhibit exceptional resistance to crystal growth or grain growth (hereinafter referred to as recrystallization), under conditions which actively promote these processes in tungsten metal. Upon rolling the unalloyed tungsten into sheet at elevated temperatures, however, it has recently been observed that the surface of the sheet has a tendency to lose its resistance to recrystallization due to some unexplained effect, believed to be surface oxidation or contamination.

In accordance with the present invention, it has been unexpectedly found that certain tungsten-rhenium alloys, in particulate, consolidated or metallurgically worked 3,399,981 Patented Sept. 3, 1968 forms, exhibit not only improved retention of fine-grain microstructure after being subjected to high temperature experiences but also exhibit improved bend and lowtemperature tensile ductility after being subjected to such high temperature experiences In addition, the novel tungsten-rhenium alloy of the present invention, as compared with the unalloyed tungsten, exhibits pronounced resistance to surface recrystallization when rolled into sheet at elevated temperatures.

In the process of the invention, tungsten hexafluoride and rhenium hexafluoride in their vapor phase are reduced in the presence of an excess of hydrogen in a fluidized bed of re fra ctg ry metal gr regfracgory metalpxide sg e d pp rt iples which may be 5 microns average" diameter or larger, and preferably at least 50 microns average diameter or larger, at a temperature suflicieutly high to effect reduction of the tungsten hexafluoride and rhenium hexafluoride to metal. The seed particles are maintained at a temperature of at least 400 F. in a fluidized state. The produced tungsten-rhenium metal alloy deposits uniformly upon the refractory metal or refractory metal oxide seed, producing, as the reaction progresses, particulate product having the 5mm a gmwingsmatrixeoimewly formed tungsifinz lmhllll wfilloy; By use of suitably purified tungsten hexaflu ride, rhenium hexafluoride and hydrogen, the deposited tungsten-rhenium alloy may be of controlled high purities, purities of 99.98% by weight and higher being readily achieved.

Flow of hydrogen, tungsten hexafluoride and rhenium hexafluoride through the bed at velocities which maintain the growing particles fluidized therein is continued and the growing particles are maintained in the bed until the resulting roughly spherical particles have reached desired size, for example 10 to 10,000 microns. Convenient final particle sizes for handling for recovery purposes and for consolidation are in the range of 200 to 600 microns. The final particle diameter may be from 2 to 3 times the average diameter of the seed, preferably at least 4 times, and up to or several hundred times the seed diameter. The upper limit of size of particulate product is only that at which it becomes impossible or inconvenient to maintain fluidized conditions with concomitant continuing growth of the particles. These particles are then recovered and constitute the novel product of the invention.

As indicated above, the seed particles employed in the process of the present invention may constitute a refractory metal or a refractory metal oxide. By the term, re-

fractory metal, it is intended that all metals which are recognized as refractory in nature and which, in a pure state have a melting point above about 1500 C. be included. Suitable refraggry metalsgedmliicles employed herein include tungsten, tantalum, niobium, molybdenum, rhenium, mixtures and alloys thereof, and the like. Preferably, the seed particles are of tungsten or of tungstenrhenium produced in a previous run of the process of the development. Suitable refractory metal oxide particles which may be employed as the seed particles include magnesia, thoria, alumina, zirconia, beryllia, yttria, urania, titania, chromia, rare earth oxides, mixtures thereof, and the like. Other useful refractory particles include tungsten carbide, zirconium carbide, and their borides, or nitrides, and the like.

tion characteristically have a metallic luster and consists essentially of a core of refractory metal or refractory metal oxide seed particles having deposited thereon an extremely fine-grain microstructure of the novel tungstenrhenium alloy, said microstructure consisting essentially of from 0.5% to 25.0%, preferably 2.0% to 10.0%, by weight of rheniurn, the balance being comprised of tungsten. This microstructure is typically comprised of (1) columnar grains having width and thickness not greater than about 4 and 12 microns, respectively, radially oriented from a seed particle of a refractory metal or a refractory metal oxide and/or (2) grains composed of concentric annular rings not greater than about 2 microns in thickness oriented around the seed particle of refractory metal or refractory metal oxide. When the seed particle is tungsten produced by reduction of tungsten hexafiuoride or the unique product of the invention, as is preferred for realization of optimum properties, the characteristic fine-grain microstructure desirably extends through the entire particle.

The novel particulate product may be consolidated directly into predetermined shape without working, and the consolidated shape may be metallurgically worked, to

produce in either event, products having outstandingly superior properties. As previously indicated, significant metallurgical and mechanical property advantages displayed by the novel tungsten-rhenium alloy in its particulate form are retained in consolidated and metallurgically worked forms produced therefrom, prior or subsequent to their subjection to hi h temperature experiences. Typically, the tungsten-rhenium alloy of the invention, in particulate, consolidated and wrought forms, retains essentially its original microstructure after being subjected to a time-temperature history of about 3270 F. for about one hour. In addition, the novel tungstenrhenium particles exhibit exceptionally high hardness, above 1,000 KHN, Knoop hardness number), as produced, and usually at least about 600 KHN after being exposed to about 2900 F. for about one hour and have densities of at least 95%, usually 97% or more of the theoretical density of said tungsten-rhenium alloy.

By means of gas-pressure bonding, the tungstenrhenium alloy particles of the invention are form'able directly into shapes of desired size and configuration, cored or otherwise, for example, bars or billets which may readily be worked as by rolling, swaging or forged into sheet bars, billets, and the like, or extruded into wire or which are capable of machining directly to a finished shape. The gas-pressure bonded shape may be machined directly at temperatures substantially below ductilebrittle transition temperatures into a finished shape. The final fabricated products, whether wrought or not, are of high tensile strength and possess unexpected and outstanding ductility, retention of tensile strength, hardness and ductility upon exposure to high temperature service conditions and a remarkable resistance to crystal growth or recrystallization under high temperature service conditions. Products made from the particles of the invention retain ductility to a surprising extent after time-temperature histories which would be expected to substantially destroy usable ductility. For example, wroughtt sheet of the tungsten-rhenium alloy particles of the invention, after exposure to about 3000 F. for about one hour, characteristically exhibit 'a ductile-brittle transition temperature (4T) below about 300- F., and generally below about 150 F.; these ductile-brittle transition temperatures are retained even after 95% or more conversion by temperature treatment of original fine-grain microstructure into large-grain equiaxed crystal. Furthermore, consolidated bodies prepared from the tungstenrhenium alloy granules of the invention characteristically exhibit, at a temperature of about 77 R, an ultimate tensile strength of at least 100,000 p.s.i., a yield strength between about 60% and 98% of said ultimate tensile strength and a measurable tensile elongation in one inch of at least.1%, after exposure to a stress relief anneal of one hour at about 1800 F., and exhibit, at a temperature of about 300 R, an ultimate tensile strength of at least 50,000 p.s.i., a yield strength between about 60% and 98% of said ultimate strength and a measurable tensile elongation in one inch of at least 1%, after exposure to a stress relief anneal of one hour at about 3600 F. In addition, a Vickers hardness number (under a 10 kilogram load) of at least 425, after being subjected to an anneal of about 2750 F. for about one hour, is characteristic of consolidated bodies prepared from the tungsten-rhenium alloy granules of the invention, previously. described. Moreover, the consolidated forms prepared from the tungsten-rhenium granules of the invention'resist recrystallization on anneals which ordinarily recrystallize at least surfaces of consolidated forms composed of unalloyed tungsten obtained by reduction of tungsten hexafluoride and completely recrystallize consolidated forms prepared from tungsten-rheniurn alloys obtained by above referred to prior art procedures. Hence, consolidated forms prepared from the tungstenrhenium alloy particles of the present invention exhibit, when sheet rolled at about 2650 F., a recrystallized surface layer less than about 1.0 mil thick after exposure to about 3250 F. for about one hour and less than about 1.5 mil thick after exposure to about 3600 F. for about one hour.

In the drawings:

FIGURES 1 through 4, inclusive, are photomicrographs illustrating the metallurgical microstructure of as-produced tungsten-rhenium alloys of the present invention having a rheniurn content of 1.0%, 2.5%, 10.0% and 20.0%, by weight, respectively;

FIGURES 5 through 8, inclusive, are photomicrographsillustrating the metallurgical microstructure of the particulate as-produced tungsten-rhenium alloys illustrated in FIGURES 1 through 4 after being subjected to severe time-temperature conditions;

FIGURES 9 through 12, inclusive, are photomicrographs illustrating the metallurgical microstructure of the particulate as-produced tungsten-rhenium alloys illustrated in FIGURES 1 through 4 after gas-pressure bondmg;

FIGURES 13, 15 and 17 are photomicrographs illustrating the metallurgical microstructure of wrought tungsten-rhenium products of the invention having a rheniurn content of 1.0%, 4.0% and 10.0%, by Weight, respective y;

FIGURES 14, 16 and 18 are photomicrographs illustrating the metallurgical microstructure of the wrought novel products illustrated in FIGURES 13, 15 and 17, after being subjected to severe time-temperature condi tions;

FIGURES 19 and 20 and FIGURES 21 and 22 are photomicrographs illustrating, for comparison purposes, the metallurgical microstructure of wrought tungstenrhenium alloys having a rhenium content of 1.85% and 3.55%, by weight, respectively, prepared by a conventional procedure, in as-produced condition (FIGURES 19 and 21) and after being subjected to severe time-tcmperature conditions (FIGURES 20 and 22);

FIGURE 23 illustrates graphically the comparison of bend-transition temperature (4T) of wrought product of the invention and of wrought tungsten-rhenium alloys, prepared by a conventional procedure, after being subjected to a severe time-temperature condition;

FIGURE 24 is a diagrammatic illustration of an apparatus for practicing the process of the invention. For simplicity and clarity in illustrating the process, the diagram omits many auxiliary items, such as reactant storagetanks and purification systems, valves, flow meters, pressure gages, safety traps, temperature controls, thermocouples and the like, although the use and application of such items will be obvious and readily apparent to one skilled in the art.

With reference to the drawings:

The fine-grain microstructure of the novel tungstenrhenium alloy of the present invention can be noted from FIGURES 1 through 4, which are photomicrographs, at a magnification of about 187 times, of as-produced tungsten-rhenium particles of the invention, produced by hydrogen reduction of tungsten hexafluoride and rhenium hexafluoride in a fluidized bed of tungsten seed particles, obtained by reduction of tungsten hexafluoride in a fluidized bed. In FIGURES 1 through 4, the photomicrographs include a cross-sectional view of at least one as-produced particle as Well as of portions of neighboring granules mounted in a hardened plastic base. The as-produced granules of FIGURES 1 through 4 are similar in that they show the deposited metal occurring in the form of concentric annular rings, which tend to be slightly wider (about one micno thick) in the granules of lowest rhenium content. The prominent band structure is attributed to cyclic deposition in the fluidized bed reactor and variation in the bands 'to statistical variations in circulation therein. The band structure, as well as the coalescence of seed particles, may be avoided in fluidized bed runs wherein seed circulation and reaction temperatures at which the seed is introduced are more closely controlled. The novel tungsten-rhenium alloy granules depicted in FIGURES 1 through 4 are of density of at least about 95% of the theoretical density of said alloy and have a hardness :of 1016, 1142, 1346 and 1307 KHN, respectively; a control sample of unalloyed tungsten prepared by hydrogen reduction of tungsten hexa-fluoride showed a hardness of 960 KHN. The individual radially oriented tungsten-rhenium crystals average about 1.5 microns in width and about 6 micnons in length. The thickness of the concentric annular rings is about 1 micron.

The remarkable resistance to crystal growth upon being subjected, to high temperature anneals for times in excess of times required to anneal compacted and sintered tungsten-rhenium powders prepared by known conventional procedures is evident from FIGURES 5 through 8 which are photomicrographs, at magnifications of 187 times, of the tungsten-rhenium particles illustrated in the as-produced condition in FIGURES 1 through 4, respectively, after being exposed to a temperature of about 3270 F. for about one hour. At annealing temperatures between about 2200 F. and 3300 F., the concentric annular rings evident in FIGURES 1 through 4, are replaced by anextremely fine-grain structure which is clearly evident from FIGURES 5 through 8. The temperature at which the rings disappeared was proportional to rhenium content, being about 2550 F. for granules having a rhenium content up to about 5.0%, about 2900' F. for granules having a rhenium content between about 5.0 and 10.0%, and above about 2900 F. for granules having -a rhenium content above about 10.0% by weight. As is evident from a comparison of FIGURES 5 through 8 with FIGURES 1 through 4, the fine-grain structure originally present in the as-produced granules was essentially retained after subjecting the granules to one hour annealing treatments at temperatures through 3270 F. In granules of FIG- URES 5 through 8, the fine-grain structures that developed on annealing appeared to consist of a single phase and the deposited metal was metallographically homogeneous with the seed material. Hardness evaluations of the granules illustrated in FIGURES 5 through 8 showed a Knoop hardness number of 588, 622, 610 and 640, respectively, after an anneal of about 3270 F. for about one hour.

The tungsten-rhenium alloy particles of the invention are convertible directly into dimensionally stable, strong ductile, predetermined shapes having the above enumerated properties. One method of producing such bodies involves placing the tungsten-rhenium alloy particles in a gastight, thin walled container of predetermined shape and dimension, packing the same by vibration, to desired extent, for example, to a bulk density of 65 percent or more of the theoretical density of tungsten-rhenium alloy, evacuating the container, and then subjecting the evacuated gas-tight container to gas pressure, time and temperature adequate to deform the container material and cause it to flow inwardly and compress the tungsten particles until they become consolidated into a unitary mass. The gas is one which, considering the conditions and container metal employed, will not penetrate the latter.

Typically, Armco iron, Zircaloy and molybdenum containers my be used with helium or argon as compressing gas under 5,000 to 20,000 pounds per square inch while maintaining the container and contents at annealing temperatures for tungsten-rhenium alloy consistent, of course, with the maintenance of the integrity of the encasing envelop as a gas-tight unit. Suitable temperatures, considering the limitations of the encasing envelop and pressure, may be in the range of about 2000 F. to about 3500 F. and above. The time necessary may vary from several minutes to several hours, depending upon the temperature used and the density of shaped product desired.

The bonding process involves deformation or flow of the individual particles to decrease interstitial volume and increase area of contact between the discrete particles, accompanied and followed by development of metallurgical bond between the particles by intercrystallization between the contiguous interfaces. At temperatures of about 2500 F. andhigher, as within the range of 2500 F. to 3000 F., the deformation processes proceed easily to a substantially impervious product (92% or higher of the theoretical density of tungsten-rhenium alloy) at times of the order of 4 hours or less, in many instances, of the order of two hours.

As previously indicated, the tungsten-rhenium particles of the invention are remarkably resistant to crystal growth upon being subjected to temperatures for times in excess of times required to anneal conventional compacted and sintered tungsten-rhenium alloy powders. However, in producing shaped articles from the tungsten-rhenium alloy product of the invention by particle consolidation only, maximum tensile strength is obtained if excess of times, i.e., times beyond those required to produce the interparticulate crystallization, are not employed. The worker skilled in the art can, with a minimum of experimentation, determine the optimum composition of encapsulating metal, time, temperature and pressure to suit the purpose of the projected use of shaped bodies of the invention.

FIGURES 9 through 12 illustrate, at magnifications of 187 times, sections of typical consolidated shapes produced by gas pressure bonding from tungsten-rhenium particle products of the invention having a rhenium content of 1.0%, 2.5%, 10.0% and 20.0%, by weight, respectively. The shapes were made by the above described technique using 10,000 pounds per square inch of helium pressure on a molybdenum capsule containing essentially spherical tungsten-rhenium particles of about 200 to 400 microns size for about 3 hours while maintaining the unit at about 2900" F. The particles used to prepare these shapes, as well as their method of preparation were described above in discussion with FIGURES 1-4.

The particulate tungsten-rhenium alloy of the invention is unique in that the final dimensions of pressure-bonded shapes made directly from the particles are so accurately predictable, the density through the pressure-bonded shape so uniform, and the strength of units such that the entire pressure-bonding operation may be confidently conducted for the purpose of yielding a pressure-bonded unit, which. without working or other processing (except possibly chemical removal of the encapsulating metal) needs only finished machining to produce a satisfactory final product. Nozzle and cone shapes are typical of those which can be produced in this way, with finished machining only to remove a few thousandths of an inch of metal from the gas-pressure-bonded shapes.

The pressure bonded shapes, with or without prior removal of the encapsulating metal, as by leveling with acid, may be worked by conventional metallurgical techniques such as by rolling, forging, drawing, swaging, spinning and the like under conditions suitable for making wrought tungsten-rhenium alloy. In rolling or forging, for example, several passes may be employed at conditions to give controlled reduction, which may be uniform, say to per pass, or to decreasing or increasing extent. Encapsulating metal may be removed after completion of the working or after any desired pass.

Working of consolidated bodies of particles of the invention may be carried out at relatively low temperatures in significantly lower than ordinarily employed with, or sometimes even suitable for, fabrication of tungsten-rhenium alloys prepared by conventional arc-melting or electron-beam melting methods referred to above. For instance, in rolling, the breakdown pass may be at temperatures substantially below 3000 F. and, in fact, for optimum development of the wrought properties of the alloy,

is preferably not in excess of 2900 F., very satisfactory to optimum results being obtained at breakdown or maximum working temperatures in the range as low as 2600 F. Successive fabrication passes may conveniently be at lower intervals of 100 F. to 300 F. In contradistinction thereto, tungsten-rhenium alloy, prepared by the above described conventional methods, often requires, for optimum development of metallurgical properties, working temperatures several hundred degrees higher, up to 400 F. or more higher, than those indicated. The resulting wrought product is, moreover, structurally inferior than those made possible by the present invention. Thus, the product of the invention provides for substantial economies of wrought material in manufacture of items meeting structural specifications, as well as superior products.

Superiority of the tungsten-rhenium particles of the invention is further illustrated by FIGURES 13 through 23.

FIGURES 13, 15 and 17 are photomicrographs at magnification of 187 times of as-rolled sheet stock, pressure bonded novel spherical particles of the invention having 1.0%, 4.0% and 10.0%, by weight, rhenium content, respectively, the sheets illustrated in FIGURES l3 and 15 being rolled to 93% reduction at a rolling temperature of about 2900 F. and the sheet illustrated in FIGURE 17 being rolled to reduction at a rolling temperature of about 2650 F. FIGURES 14, 16 and 18 are photomicrographs at magnification of 187 times of the sheet stock illustrated in FIGURES 13, 15 and 17 after being heated for about one hour at a temperature of about 3260 F. These rolled products maintained high hardnesses, exhibiting Vickers hardnesses (under a 10 kilogram load) of about 460, 378 and 454, respectively, and showed little evidence of recrystallization, i.e., percentage of crystals determined by microscopic examination to have been converted by the time-temperature experience to equiaxed large grained form, undergoing only 13%, 16% and 20% recrystallization, respectively.

FIGURES 19 and 21 are photomicrographs (187 times) of as'rolled tungsten-rhenium alloy sheet stock having a rhenium content of 1.85% and 3.55%, by Weight respectively; these sheet alloys were prepared from a blend of 325 mesh commercially pure (undoped) tungsten powder and -200 mesh commercially pure rhenium powder which was compacted into electrodes, sintered at 4100 F. and consolidated by triple electron-beam-melting. FIGURES 20 and 22 are photomicrographs at magnification of 187 times of the sheet stock illustrated in FIGURES 19 and 21 after being heated for about one hour at a temperature of about 3250 F. These rolled products were fully softened, exhibiting Vickers hardnesses (under a 10 kilogram load) of 361 and 325, respectively, and were each fully recrystallized.

It is apparent from comparison of FIGURES 13 through 18 with FIGURES 19 through 22 that the Wrought form of the tungsten-rhenium alloy particles of the invention retains a significantly greater proportion of fine-grained structure than the wrought tungsten-rhenium alloys prepared by conventional procedures after extreme temperature exposure. FIGURES 20 and 22 show that the wrought product made from electron-beam melted tungsten-rhenium alloys after high-temperature service became essentially completely recrystallized. By contrast, FIGURES 14, 16 and 18 demonstrate that wrought product made from particles of the invention resists recrystallization during high-temperature service to outstanding degree, retaining to surprising extent after such service original crystal structure and, hence, tensile strength, ductility, workability and utility for service of this type. The retention of strength and hardness after high-temperature service, as well as superior strength throughout an extended high-temperature range, permit substantial economies of alloy and consequently of weight for structures intended for high-temperature service.

FIGURE 23 illustrates the changes in the minimum temperature at which a rolled sheet, which has been subjected to a temperature of about 3000 F. for one hour, may be bent without cracking over a are having a radius of four times sheet thickness. It is evident from FIGURE 23 that fabricated products of the invention (represented by Curve A) retain values in this respect below 300 F., and usually below about F., despite time-temperature histories which normally result in from substantial to essentially complete recrystallization. By contrast, to achieve this efiect, rolled sheet made from electron-beam melted tungsten-rhenium alloys prepared in the above described manner (represented by Curve B) require a substantially higher rhenium content, generally at least about five times higher, on a weight basis, as required by fabricated products made from tungsten-rhenium alloys of the present invention. Illustratively, in one specific comparison, a sheet rolled product produced from tungsten-rhenium alloy of the invention having a rhenium content of about 4.0%, by weight, exhibited a bend transition temperature (4T) of about 104 F. after annealing for one hour at 3000 F. while sheet rolled products prepared from electron-beam-melted tungsten-rhenium alloys required a rhenium content in excess of about 20%, by weight, to achieve this effect. This ability to bend without breaking at low temperatures after severe high-temperature history is a measure of the ability of the product in high temperature service to withstand thermal shock and other stresses encountered in service at high temperature. One indication of the ductile-brittle transition temperature of tungsten-rhenium alloy products is that the minimum bend transition temperature normally represents about the minimum temperature at which ma chining of the product may be undertaken with reasonable assurance that it is not too brittle for the machining operation. Surprisingly, shapes made from particles of the invention are machinable at substantially lower temperatures, even at room temperature, with conventional machining conditions.

Further, as indicated above, tungsten-rhenium alloy products of the present invention characteristically reflect excellent low-temperature tensile ductility both as rolled and after annealing to high temperatures. Tensile properties (determined by ASTM E857T and E2l-58T) of representative sheet alloys produced from tungsten-rhenium alloy particles of the invention and of sheets made from electron-beam-melted tungsten-rhenium alloys are summarized in Table I, below, all sheet samples being electropolished prior to testing. In Table I the material designated as, A, represents sheet produced tfrom tungstenrhenium alloy particles of the invention having a rhenium content of 4.0%; the material designated as, B, represents sheet produced from electron-beam-melted tungstenrhenium alloy particles having a rhenium content of 1.85%; and the material designated as, C, represents sheet produced from electron-beam-melted tungsten-rhenium alloy particles having a rheniumpontent of 3.55%.

TABLFl I material which does not react with the reactants. Suitable metals include high nickel content alloys of copper and Ultimate Yield Test Tem- Tensile Strength Elongation Material Test Conditlon perature Strength, (0.2% percent in F.) 10 psi. offset) one, inch (10 p.s.i.)

25 160 110 1.6 150 154 140 6.0 25 171 150 10. 25 97 0 25 156 0 25 149 4. l 91 0 do 25 85 0 A" Stress relief anneal at 3,632 F. for one hour. 150 99 8. 8 g" Stregs relief anneal at 3,500 F. for one hourg5 0 -5 0 It is apparent from the results of Table I that shaped or final products made from novel tungsten-rhenium particles of the invention possess markedly superior low-temperature elongation, as'compared with products made from electron-beam-melted tungsten-rhenium alloys.

A unique property of tungsten-rhenium particles of the invention resides in the fact that by a single step, gaspressure bonding as described above, the particles may be converted to a solid unit of predetermined size and shape having density which may approach the theretical density of tungsten-rhenium alloy. If the optimum in strength is desired, density of the shape should be 92% or higher of theoretical. These consolidated-only products have structural and other properties of wrought products made therefrom and, like wrought tungsten-rhenium products produced therefrom, may be cold machined directly into a desired finished shape having said service characteristics, for example, those required in high-temperature services, for example, in rocket components, such as nose cones on missiles in atmospheric re-entry applications or as in uncooled rocket nozzles. Sintered tungsten-rhenium powder shapes, even though carefully prepared under conditions yielding a sinter of maximum density, do not possess such properties. Moreover, the high density bonded particles of the invention are so uniform in structure and have dimensional predictability of such a high order that in many instances the bonded shape as produced requires only finish machining.

' As more fully abovedescribed, another unique propertyof tungsten-rhenium products of the invention lies in the ability of rolled sheet produced from such particles to retain ductile-brittle transition temperature below about 300 F. or less, even after essentially complete conversion by temperature treatment of original fine-grained microstructure into "large-grained equiaxed crystal. Such material is capable of withstanding thermal shock de'spite'its essentially complete recrystallization, as are unrolled substantially completely recrystallized gas-pressure bonded shapes. Furthermore, the improved high-temperature properties of the" tungsten-rhenium alloy particles of the present invention render products prepared therefrom amenable to fabrication into a variety of useful sheet metal shapes with a minimum of difliculty; for example, there is no need for elaborate hot-form equipment/These shapes include specific articles such' as curved leading edge members for wings on control surfaces on re entry space vehicles, channel or corrugated structural panels as' supports for high temperature application's,'flat or contoured skins for hot structures such as entrance caps for solid fueled rocket nozzles. The ability of products made from tungsten-rhenium alloy particles of the present invention to retain a high degree of ductility after high temperature cycling enhances their usefulness in the type of application previously described, for example, the structural integrity of re-entry space vehicles are maintained after extreme cyclic temperature variations. FIGURE 24 of the drawings illustrates one mode of effecting the process of the invention in which there is shown a reactor, generally designated 3;of a suitable nickel such as Monel metal. Copper is a useful material for inlet and exit lines. Tetrafluoroethylene polymers and chlorotrifluoroethylene polymers are useful for gaskets and for flexible lines. The reactor 3 comprises a vertical tubular-shaped section 4 providing a reduction zone '5, tapered into lower conical section 6 and flaring gradually outward into an upper section 7 which is closed by a top 8 which may be provided with a suitable safety vent 15. Lines 9 and 10 are provided to introduce the reactants, hydrogen, tungsten hexafluoride and rhenium hexafluoride, into the system to flow as a mixture into lower conical section 6, and upwardly through reduction zone 5.

Line 11 is provided through top 8 to introduce refractory metal or refractory metal oxide seed particles into reactor 3, wherein they drop into the reduction zone 5. Heater means 12, such as electrical resistance coils, or induction heaters, or a gas fired furnace, surrounding the reduction zone, heat the particles therein and maintain them at a suitable temperature for the hydrogen reduction of tungsten hexafluoride and rhenium hexafluoride. Re-

', action temperature may be in the range of about 400 F. up to a temperature of 2000 F. or somewhat higher. In

, accrues by use of temperatures substantially above this level. In fact, use of the process has demonstrated that quite satisfactory commercial operating temperatures lie in the range of about 1000 F. to 1200 F., as for example about 1100" F. to 1150 F. At temperatures below about 1200 F. or with low excesses of hydrogen, substantial quantities of unconverted tungsten hexafluoride and/or rhenium hexafluoride tend to exit the reaction zone. Within the reduction zone 5, the upwardly flowing hydrogen, tungsten hexafluoride and/or rhenium hexafluoride, and, as it is produced, hydrogen fluoride, function to fluidize the seed particles. Under proposed operating conditions, the volume of hydrogen greatly exceeds the volume of tungsten hexafluoride and rhenium hexafluoride and hence serves as the primary'fluidizingcomponent at the outset of the reaction, its eflfect being augmented by produced hydrogen fluoride. Within reduction zone 5, the tungsten hexafluoride and rhenium hexafluoride are reduced to tungsten metal and rhenium metal which deposit on the fluidized metal seed particles producing, by growth to predetermined extent, the unique tungsten-rhenium alloy particles of the invention. As the gases enter expanded upper section7, the resulting decrease in their velocity is to below fluidizing level; hence, the lower end of section 7 defines the upper level of the fluidized bed. Finally, the gases exit the reactor by upper discharge line 14. At this point they might contain finely divided solids which may be separated from them and returned to the reactor by known means.

' The reactor may be operated on abatch basis or with continuous introduction of seed and continuous withdrawal of produced particles from the fluidized bed, for example, at a level adjacent the bottom, as throughline 13. The continuously withdrawn particles are then pref- 1 1 erably subjected, possibly after purging of accompanying gas therefrom, to desired classification procedure to generate out finished product of desired size. Smaller particles are then returned to the reactor, for example, with the feed or fresh seed.

million, usually 50 parts per million or less. The unique crytalline and other properties of the product of the illvention are unexplainable under any theory concerning the nature and extent of usual impurities present, but possibly might be'attributable to the presence of the small O The system shown in FIGURE 24 is primarily adapted quantity of fluorine, the form of which is not known, exfor batch operation, in which feed of hydrogen, tungsten cept occurrence as fluoride ion. hexafiuoride and rhenium hexafiuoride is initiated through As indicated hereinabove, the quantity of hydrogen gas a precharged bed of refractory metal or refractory metal employed must be in excess of the stoichiometric equivoxide seed and maintained for times, depending upon realent of the tungsten hexafiuoride and rhenium hexaaction temperatures and proportion of feed components fluoride feed. The extent of the excess required to effect selected, which will produce the desired size of product Complete reduction of these metal hexafiuorides to metal particle. At the end of that time, which can be selected tends to be a function of reaction temperatures. A guide quite readily with experience with the operation, the feeds for select1on of satisfactory proportionate quantities of are discontinued and the reactor is purged of combustible l5 reactants may be the fraction represented by one-third of and corrosive substances by inert gas, typically argon the number of moles of hydrogen fed over the total of or helium, admitted through line 16. The tungsten product the number of moles of tungsten hexafiuoride and rhenium may then be withdrawn through line 13 immediately or hexafiuoride feed. At temperatures of the order of 400 after a desired cooling period. in general, the mole ratio F. that fraction should be about 50 or higher, at 1000 of rhenium hexafiuoride to total metal hexafiuoride, i.e., F. to 1200 F. about 10 or higher and at 1825 F. and tungsten hexafiuoride plus rhenium hexafiuoride, charged higher may be 1.5 to 2 or higher. into the reaction zone may range from about 0.01 to Specific examples of the invention are summarized in 0.50 or higher, although mole ratios of rhenium hexa- Table 11.

TABLE II Seed Particles Process Conditions Produ t Reduc- Stoichio- R0 Produc- Re Av. Mesh Wt, tion metric Feed, Mole Duration Content, tion rate, Recov- Example Material Dia. Size grams Zone, excess of Ratlo of Run, Wt. ./hr,, cry,

(,1) Temp., Hydrogen 11 ROFG Mm. percent tt. percent F. WPr+ReFt 1 w Particles 9s 140+170 100 1,030 3.13 0.0103 33 2 Product Example 1 100 1, 036 3.78 0. 0103 81 3 Product Exumple2 100 1.036 15.7 0.0103 81 4 o 100 1.036 15.7 0.0097 81 5 w Particles"... 9s -119+170 100 1,030 2.70 0. 0199 82 6. Product Example5 I 100 1,036 3. 64 0.0193 82 7' Product Example 0 100 1,030 13.5 0. 0210 83 s .do 100 1.030 15.3 0.0190 80 9 W Particles 08 140+l70 100 1,036 2.95 0.0292 82 10.. Product Example9 100 1,036 3.41 0.0297 82 11.. Product Example 10. 100 1, 030 10.1 0. 0268 so 12.. 100 1,030 13.4 0.0208 31 13.. 030 2.95 0.0444 117 14.. Product Example 13- 980 2. 87 0.0301 110 Product Example 14 986 11. 3 0. 0400 100 do..- 930-1, 030 15. 2 0. 0400 as W Particle 986 3. 1 0. 0421 131 ass 3. 7 0. 0421 130 1,030 17. 0.0421 100 (1 1, 036 16. 0. 0411 so 1, 030 17. 0. 0400 00 2 .do 1, 030 10. 0. 0400 07 H2 l One-third the mole ratio WFH-ReFu fluoride to totaLmetal hexafiuoride between about 0.02 n The examples numbered as indicated were effected to 0.10, yielding tungsten-rhenium alloy particles having during batch operation of a one-inch internal diameter a rhenium content between about 2.0% and 10.0%, by Monel metal vertical reactor which was externally heated i ht, r r f rred by electrical resistance units. The runs were initiated by Gases exiting the reactor by line 14 contain hydrogen, charging into the reactor refractory metal seed particles HF, and, depending upon the temperature and proporof the material, size and quantity (weight) indicated, tions of feed components selected for the reaction, may purging the reactor with argon, fluidizing the reac.or also contain some tungsten hexafiuoride and/or rhenium contents with palladium diffused hydrogen, heating the hexafiuoride. Under preferred conditions, however, there seed to the temperature indicated, thereupon admitting, is virtually no metal fluoride present. For economical separately or mixed, commercial distilled tungsten hexaoperation the exhaust gases are preferably processed by fluoride and rhenium hexafiuoride to the bottom of the techniques which will be apparent to those skilled in the reactor, adjusting the feed of hydrogen to about M; cubic art to separate hydrogen in very dry air-free form for feet per minute standard conditions and the feed of tungreuse and, if it is present, to recover tungsten fluoride sten hexafiuoride and rhenium hexafiuoride to maintain and/or rhenium fluoride. the H /WF -ReF ratio indicated and maintaining the In order to develop to the optimum extent the desirable conditions described for the time shown. At the end of properties of the unique product of the invention, the that time the heating and flow of metal fluoride were hydrogen, tungsten hexafiuoride and rhenium hexafiuoride discontinued and hydrogen flow continued until bed feeds should be of such purity as to yield a product which, temperature declined below about 100 F. The products except for fluorine content, has a purity of at least about were generally spheroidal in shape and contained the 99.8% tungsten-rhenium, by weight. Products of this quantity of tungsten and rhenium in the original hexa purity and, in fact, of purity of 99.95% or more tungstenfluoride feed to the extent tabulated, the deposition having rhenium, by weight, may be readily obtained by using been made at the rate persquare foot of reactor area distilled tungsten hexafiuoride and rhenium hexafiuoride shown. sold commercially and hydrogen diffused through pal- Upon beginning operation, the particles of seed plus ladium. The product contains characteristically the iminitially deposited tungsten and rhenium conform roughly purities present in tungsten-rhenium alloys produced by in shape to that of the seed granules. As operation conother methods plus fluorine in up to about 100 parts per tinues, the particles grow in size and gradually become spheroidal in shape and ultimately approximate spherical shape. For high quality of tungsten-rhenium alloy product, tungsten and rhenium of the type deposited by the process of the invention should constitute at least the predominant proportion of the final particulate product. When the seed is obtained by use of that process, the final particles are all or substantially all constituted by the normal deposited tungsten and rhenium. When the seed is a different tungsten or tungsten-rhenium alloy, deposition should be continued until deposited tungsten-rhenium 1 aggregates at least double the weight of the seed. Continuing the process under the conditions of Example 1 until ultimate particle size is 300 to 400 microns results in product in which the average particle contains a tungsten-rhenium deposit of about 92 to about 97 percent by weight of product made during the run, while continuing until ultimate particle size is about 600 microns results in product in which the average particle size contains a tungsten-rhenium deposit of greater than 99 percent by weight of product made during the run.

Since various changes and modifications may be made in the invention without departing from the spirit thereof, it is intended that all matter contained in the above description be interpreted as illustrative and not in a limiting sense.

We claim:

1. A tungsten-rhenium alloy in the form of substantially spherical particles consisting essentially of a microstructure of (1) columnar grains having width and thickness not greater than about 4 and 12 microns, respective- 2. The alloy of claim 1 in which said particles, upon gas-pressure bonding at about 10,000 p.s.i. and about i 2900" F. for about 3 hours, yield a unitary consolidated body of at least 92% of the theoretical density of said alloy, said consolidated body being rollable to 80-95% reduced product having a ductile-brittle transition temperature below about 300 F. after exposure to about 3000 F. for about one hour.

3. The alloy of claim 2 in which said consolidated body, in wrought form, is characterized by exhibiting at a temperature of about 77 F., an ultimate tensile strength of at least 100,000 p.s.i., a yield strength between about and 98% of said ultimate tensile strength and a measurable tensile elongation of at least 1% after exposure to a stress relief anneal of one hour at about 1800" F.

4. The alloy of claim 2 in which said consolidated body, in wrought form, is characterized by exhibiting at a temperature of about 300 F., an ultimate tensile strength of at least 50,000 p.s.i., a yield strength between about 60 and 98% of said ultimate tensile strength and a measurable tensile elongation of at least about 1% after exposure to a stress relief anneal of one hour at about 3600 F.

5. The alloy of claim 2 in which said consolidated body, after said rolling, is characterized by having a Vickers hardness number of at least 425 after exposure to about 2750 F. for about one hour.

6. The alloy of claim 2 in which said consolidated.

body is characterized by exhibiting, when sheet rolled at about 2650 F., a recrystallized surface layer less than about 1.0 mil thick after exposure to about 3250" F. for about one hour and less than about 1.5 mil thick after exposure to about 3600 F. for about one hour.

7. A tungsten-rhenium alloy in the form of substantially spherical tungsten-rhenium particles of 10 to 10,000 microns diameter, said particles consisting essentially of a microstructure of (1) columnar grains havingwidth and thickness not greater than about 4 and 12 microns, respectively, radially oriented from a seed particle of a refractory metal or a refractory metal oxide, and/or (2) grains composed of concentric annular rings not greater than about 2 microns in thickness oriented around the seed particle of refractory metal or refractroy metal oxide, said microstructure (21) consisting essentially of from 2 to 10% by weight of rhenium, the balance being tungsten, (b) having density of at least 95% the theoretical density of said alloy and (c) exhibiting essentially said microstructure upon being subjected to about 3270 F. for about one hour; which particles, upon gas-pressure bonding at about 10,000 p.s.i. and about 2900 F. for about three hours, yield a unitary consolidated body having a density of at least 92% of the theoretical density of said alloy, said consolidated body being rollable to -95% reduced product having a ductile-brittle transition temperature below about 300 F. after exposure to about 3000 F. for about one hour.

8. The alloy of claim 7 wherein said consolidated body, in wrought form, is characterized by exhibiting, at a temperature of about 77 F., an ultimate tensile strength of at least 100,000 p.s.i., a yield strength between about 60% and 98% of said ultimate tensile strength and a measurable tensile elongation of at least 1% after exposure to a stress relief anneal of one hour at about 1800 F. and by exhibiting, at a temperature of about 300 F., an ultimate tensile strength of at least 50,000 p.s.i., a yield strength between about 60% and 98% of said ultimate tensile strength and a measurable tensile elongation of at least 1% after exposure to a stress relief anneal of one hour at about 1800 F. and by exhibiting, at a temperature of about 300 F., an ultimate tensile strength of at least 50,000 p.s.i., a yield strength between about 60% and 98% of said ultimate tensile strength and a measurable tensile elongation of at least 1% after exposure to a stress relief anneal of one hour at about 9. The alloy of claim 8 wherein said seed particle is of tungsten and said consolidated body is rollable to 80- reduced product having a ductile-brittle transition temperature below about F. after exposure to about 3000 F. for about one hour.

10. The alloy of claim 9 wherein saidseed particle is of an alloy of tungsten and rhenium containing between about 0.5% and 25.0% by weight of rhenium and said consolidated body is rollable to 8095% reduced product having a ductile-brittle transition temperature below about 150 F. after exposure to about 3000 F. for about one hour.

References Cited UNITED STATES PATENTS 3,062,638 11/1962 Culbertson 75.55 3,177,067 4/1965 Nichols 75.5 X 3,178,308 4/1965 Oxley l17l07.2 X 3,234,067 2/1966 Blocher ll7100 X 3,236,699 2/1966 Pugh 75207 X 3,341,320 9/1967 Smiley 75.5 3,300,285 l/1967 Pugh 75207 X 3,343,979 9/1967 Hamrin ll7-107.2 X

OTHER REFERENCES The Formation of Metallic Coatings, Powell, Metal Finishing, April 1952 pp. 64-69.

Treatise on Powder Metallurgy," vol. I, Goetzl, 1950, pp. 1-11.

CARL D. QUARFORTH, Primary Examiner.

A. I. STEINER, Assistant Examiner.

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