US1236384A - Alloy of tungsten and molybdenum. - Google Patents

Description

F. A.FAHRENWALD.

AL-LoY or TUNGSTEN AND MoLYBDENuM.

APPLICATION FILED JUNE 3.1916' Patented Aug. 7, 1917.

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UNITED sTATEs PATENT oEEicE.

FRANK A. FAHRENWALD, OF CLEVELAND, OHIO, DEDICATED, BY MESNE ASSIGN- MENTS, TO THE GOVERNMENT OF PEOPLE OF THE UNITED STATES THE UNITED STATES OF OF AMERICA.

AMERICA AND T THE ALLOY OF TUNGSTEN AND MOLYBDENUM.

Specication o'f Letters Patent.

Patented Aug. '7, 1917.

Application led J une 3, 1916. Serial No. 101,502.

(DEDICATED T0 THE PUBLIC.)

- ing at Cleveland, in the county of Cuyahoga and State of Ohio, have invented a certain new and useful Improvement in Alloys of Tungsten and Molybdenum, of which the following is a full, clear, and exact descrlption, reference being had to the accompanying drawings.

This application is made under the act of March 3, 1883, chapter 143 (22 Stat. 625) and the invention herein described and claimed may be used by the Grovernmentoi:l the United States, or any vof its officers or employees in the prosecution of work for the Government or by any person in the United States without the payment of any royalty thereon.

This invention relates to a composition of matter containin tungsten and molybdenum together with t e process of making the., same. `Owing to the extremely elevated` melting points of these materials it has so far been impossible to alloy either with the other or with any other substance by the usual fusion methods. The present invention relates to the method of incorporating these two metals together without the necessity for fusion, and subsequently, by repeated mechanical working under predetermined temperature and metallographic conditions, to reduce the composition to such a state of duct-ility, malleability, and tensile strength as shall fit it for use in the arts.

My researches have shown that the strength and ductility of these metals depend upon the fostering of an amorphous condition therein, as against a' crystalline condition, and I have discovered that the said amorphous condition, while it-can be secured by mechanical working with the somewhat indefinite time and temperature conditions set forth in the Coolidge Patent No. 1,082,933 dated December 30, 1913, can he secured far more exactly and positively by a system of heat treatment using times and temperatures much different from those suggested in that patent; and as regards the production of a composition containing both tungsten -and molybdenum, such metallolmolecules at temperatures graphic control is absolutely prerequisite to the obtaining of a practical material.

It has for some time been suspected that the elasticity and tensile strength of metals were due largely to the occurrence of such metals in an amorphous form, and these qualities were seriously impaired by vtheir occurrence in or reversion to a crystalline form. @ne indication of this resides in the fact that crystalline metals when fractured always break across crystals, and never where the adjoining crystals meet. For this same reason, metals having large or coarse crystalline texture are always far inferior in strength to those having a line grained crystalline structure. It has also been noted that the crystalline structure can be broken up by suitable mechanically cold working so as to increase the amorphous condition and with it the strength of the material. Following the studies of Rosenhain and Ewing (Philosophical Transactions, Vol. CXCIII, page 355-1900; and Proceedings of the Royal Society, Vol. CXC, page 85-1899) my researches show that upon the occurrence of the necessary mechanical stress each crystal becomes sheared into a larger or smaller number of leaves or plates which slide one upon the other, the metal along these lines or planes of shear being temporarily liquefied by the strain and changed from the crystalline to the amorphous condition, this amorphous material thereafter binding the crystal plates together as a kind of cementing material which is both harder and stronger than the crystalline material which it surrounds. (See Transactions o the American Institute of Mining Engineers, February 1916, pp. 103-149.)

Ordinarily this distortion is not carried to the stage at which the crystals are completely converted to the amorphous form,

metastable condition. In the case of ordinarily undercooled liquids, the presence of the stable (crystalline) form tends to produce true equilibrium immediately, but in the case of metals, the sluggishness of the so far below their normal melting point under normal pressure as our ordinary temperatures preventsthis transformation. However if the temperature be raised considerably, even to a point short of complete fusion', the kinetic energy of the molecules rises until, at a certain point, the fragments of crystals which remain are able to impress their orientation upon the molecules of the'amorphous substance and thus slowlyrestore it to the crystalline condition. This restoration may be effected either by the subjection of the material to a high temperature for a short time, or to a comparatively lower temperature for a longer time, just as the temper of a steel tool may be drawn either by subjecting it for a few minutes to the action of the tire or by allowing it to lie in the sunlightA for a few days or weeks.

It will be evident from the foregoing that for each metal there must be a critical timetemperature relation, above which the kinetic `energy ofthe molecules is so great as to permit their returning at once to the crystalline form when displaced by mechanical distortion, and below which, mechanical workings will produce a permanent amorphous condition.

If force be applied to any crystalline metal at any temperature suiliciently elevated so that the kinetic energy of the moleeules is able to restore a crystalline condiordinary room temperatures.

tion after the withdrawal of the force, no permanent amorphous condition of the material.is secured. It is not even certain that even a temporary amorphous condition results, though it is probablethat such is the case during the time that the force is actually exerted; however the equiaxing forces are exerted immediately upon the' withdrawal of the impressed force and the permanent condition of the metal is not at all changed. This operation is called hot working and the temperature at 'which "such hot working begins varies for every metal. For example hot working of tungsten does not begin until some 1800 C., but hot working of gold is accomplished only slightly above ordinary room temperatures.

' If the temperature of the metal is below a certain critical point, then any force impressed from without tending to change the shape or condition of the crystals will produce a per nanent change therein with the creation of a permanent amorphous condition, the kinetic energy of the molecules being too small to produce any equiaxing. This oper/ation is called cold working, and for tungsten this temperature ranges down- /w'ardly from about 1800 C. For gold this temperature begins at some point near our Y j However if such a metal, after being cold-worked for a time, be temporarily subjected to the temperature of hot worklng the equiaxing effect will be produced and the traces of cold work- 1,2se,a

ving will be more or less completely removed depending upon the temperature, the time,

thin edge of any metal whatever wherein the process of cold working has been carried out to a very complete extent, the qualities of hardness, stiffness and ductility produced will b e accompanied by such `anintense molecular strain that a degree of eqaiaxing will be produced ina shorter time or with lower temperatures than in a case where the crystal structure has not been so completely broken down.

While it is obvious from the foregoing that no amorphous condition can be obtained in any metal by working the same mechanically a'bove itsV critical temperature, it has also been known empirically that for many metals a certain minimum temperature is necessary for the beginning of the deforming operation since below that temperature the metal will not respond whatever but will break or fly to pieces. This is exhibited by bismuth and antimony at ordinary temperatures; by tin and zinc in winter weather; by iron, steel, copper, gold and nearly all metals at the low temperatures produceable by liquid air. However there is for each metal a. range of temperatures, below the critical point whore hot working leaves off, during which the crystals retain such a de-A grec of plasticity as to admit of mechanical working with thc production of a certain amount of amorphous material and Without. 1o@ the immediate return of such `amorphous material to the crvstalline condition. After the production of this amorphous material has commenced in a more or less uniform way throughout the mass the temperature 105 of the working can be gradually decreased,

since the amorphous material appears to prevent the disruption of the metal, and the production of new amorphous material is correspondingly accelerated. i

My experiments show that with tungsten, molybdenum and gold the amorphous condition is produced most quickly and in the largest possible degree when the cold working of the metal is commenced at the lowest practicable temperature, although this temperature will vary depending upon the violence of the mechanical forces to which the mass is subjected. Thus if metallic crystalline tungsten is merely forged by hammering between comparatively flat surfaces, a metal will preserve its integrity at aconsiderable lower temperature than if it be i swaged, rolled, drawn or otherwise more vigorously distorted.

I have also discovered by practical experiments (which in this case serve merely to verify the results of logical deduction) that the maximum amorphous'condition is secured, and is secured in most uniform 130 heat-treatment violent distortion be secured measure, when the structure of the tungsten metal at the beginning of the mechanical cold-working consists of a uniform formation of comparatively fine crystals, and I have found that this uniform fine crystalline structure can be secured, with pure tungsten, pure molybdenum, and with alloys of the two in any desired proportion, by sultable of the material just prior to the beginning of the cold-working. In the case of both of these metals, the reduction temperature is far less than the fusion temperature, wherefore the metallic substances are originally obtained in the form of amorphous powders. These powders, either pure, or mixed in any desired proportion, are compacted into briquets under great pressure (about 200,000 pounds per square inch). I have found that with a tungsten briquet of this nature the most satisfactory crystalline condition was obtained when the material was subjected for about 10 minutes to a temperature of about 26000 C. which resulted in a very finely crystalline mass with many intercrystalline boundaries not clearly defined and appearingto indicate the presence of amorphous material even before mechanical working was begun. If the temperature is increased much above 2600o C. the briquet becomes more coarsely and irregularly crystalline, and at temperatures much less than 26000 the crystalline structure is scarcely sufliciently pronounced to form a good departure for mechanical working.

My researches also show that within certain limits the lower the sintering or heattreating temperature, the higher is the initial temperature necessary for forging. While, on theory, cold-working is more important than hot-working to produce the amorphous condition desired, yet the cold-working stage must be approached by such'slow degrees as shall prevent the destruction of the material in the process; for until suflicient amorphous material has been built into the metal by mechanical working at elevated though constantly decreasing temperatures, the metal will not admit of any cold-working whatever. However it is desirable on theory, and experiment fully substantiates the same, that the lower the initial forging temperature, the more rapid and uniform is the growth of the amorphous condition. I have discovered that with pure tungsten subjected to the heat-treatment above suggested, towit 2600o C. for ten minutes, the forging temperature is only about 1275 C., which is lower than can be obtained under any other conditions. For practical shop-Work I recommend an initial forging temperature somewhat higher than this in case 'a more as by swaging or rolling; say about 1500 C.

With pure molybdenum, the same condi-,

tions are present, though the time and temperature required for heat treatment and the. temperature required for the forging are both lower than for the treatment of tungsten. I have obtained the best results when a briquet made under a pressure of about 200,000 pounds per square inch was subjected for about one minute to a temperature of about 2300o C., which resulted in a very finely crystalline ingot of rather homogeneous condition. This ingot could be forged like tungsten, though at a slightly lower temperature, approximately 1000o C.

yWhen the ingot is made of a mixture of molybdenum and tungsten metals it is found that the formation of crystallites and crystal growths proceeds in the same manner as with the separate metals, (due to the fact that the same are mutually soluble in all proportions in the solid state) although the temperature representing a certain grain size changes with the relative amounts of the components, as shown in Fig. 4. This temperature bears a somewhat uniform relation to the proportions of the'ingredients as is shown by the continuous inclination of the treating-temperature curve, but it is curious to note that the forging-temperature curve bears a completely different relation, being substantially at a maximum when equal parts of the two metals were employed, and at a minimum in the case of the pure materials.

The mixed metals when treated in this way form true solid solution alloys. They possess the qualities of ductility, malleability, rigidity, elasticity and tensile strength in a most remarkable degree. and microscopical examination shows that the ingredients form a complete series of solid solutions. depending however upon mechanical working and not upon fusion due to heat. By the process herein described I have been enabled to produce articles of tungsten, molybdenum, and of their alloys more cheaply and certainly than heretofore and of a more uniform texture and of a high degree of mechanical reliability. These materials, on account of their cheapness, strength, and resistance to corrosion are peculiarly advantageous in many dental, scientific, and philosophie uses.

In many cases one of tungsten and molybdenum superior to either of the metals alone. Thus in dental use, as in dental pins, it is frequently desirable to employ a rod or wire of great stiffness and reliability, yet with a minimum of size, owing to the importance of avoiding unnecessary weakening of the foundation structure. In many respects tungsten appears to form an extremely satisfactory material for this purpose, especially when coated with gold or other non-oxidizable metal as described in my Patent No.

these alloys of will be found far 1,228,194, issued May 29, 1917. However the ductile tungsten, even when made with the most extreme care, frequently exhibits treacherous spots where the crystallization system has either reasserted itself or has not been suiciently overcome. A11 alloy of tungsten and molybdenum is found to possess even greater strength, hardness and ellasticity than either tungsten or molybdenum alone, and responds to the cold-working process in such a way that the treacherous spots are less frequently found than in pure tungsten: also the equiaxing temperature of the alloy is higher than that ,of either of the component metals, so that the annealing of the same under ordinary manipulation is less tobe feared.

In the drawings accompanying and forming a part of this application I have illustrated certain steps and characteristics of the discoveries and inventions hereinbefore described. In these drawings Figure 1 is a perspective view of a part of al briquet mold, illustrating also a briquet from which my improved alloy is made; Fig. 2 is avertical sectional view through a resistance furnace of the type wherein said briquet may be heat-treated and forged; Fig. 3 is a chart illustrating the relation between the heat treating tempera-tures and forging temperatures of tungsten and molybdenum separately; Fig. 4 is a similar chart showing the treating and forging temperatures of tungsten-molybdenum series.-

Describing the parts by reference characters, 1 represents one side of a briquet mold, with which there is employed a second identical member (not shown). These mold members are secured tightly together by suitable bolts passing into the apertures 2 2, and are secured to a suitable base member 3 by the use of other bolts passing 'through the apertures 4 5. The adjacent faces of the members 1 1 are notched as shown at 6, and in the mold space thus formed the finely divided metals, after being 'thoroughly mixed in the proportions desired, are compacted into a briquet 7 by the employment of high pressure as by a hydraulic press or like device.

In Fig. 2 I have illustrated a resistance furnace in which the said briquet is introduced for its next treatment. 10 represents the base of the furnace'which may be of fire clay or the like, andll the body of the furnace which is also of refractory material preferably embraced by a casing 12. Projecting through the bottom of the furnace is a post 13 preferably of copper secured to a foundation plate`14 to which is attached the electric cable 15. The top of the post 13 is provided with an electrode point 16., preferably of fusedtungsten, above which is a second movable similar electrode point 17 secured to the lower end of the bar 18 which and is provided with the striking head 20 to which is attached a second cable 21. A coil spring 22 serves to support more or less of the weight of the bar as may be desired, while a suitable sleeve 23 of refractory material inside the furnace restrains the flow of gas therethrough. Other shields at 24 may also be employed if desired. The briquet 7 is introduced between the terminals 16. 17, directly beside an observation window 25 formed in the furnace wall, through which heat determinations may be made by the use of a suitable pyrometer. A reducing gas like hydrogen or an inert atmosphere like nitrogen is introduced by way of the tube 26 and finds its way out through the various apertures. In use the member 14`is suitably supported, the parts arranged as illustrated, and the desired .temperature Ais secured by passing current through the cables 15 andv 21 for the time required. The temperature is then allowed to fall to the desired forging point, after which forging is begun by hammering upon the terminal 20, the furnace being allowed to cool in proper degree during and between the forging operations.

After the formation of a suitable degree of amorphous condition under this forging operation, the material can be swaged, rolled,

drawn or otherwise worked to the required elasticity, ductility and tensile strength.

In Fig. 3 the curve 30 illustrates the relation between the heat-treating and forging temperatures for pure tungsten, and 31 the similar relation for molybdenum In each case it will be seen that the curve exhibits a marked angularity and my experiments show that the most satisfactory metal condition is secured with heat-treatments and forging temperature corresponding to this point. In the case of an alloy of tungsten and molybdenum this minimum forging temperature vis increasedin each case over its value for the'pure metal, its maximum being reached with an alloy of equal parts of the two metals, as shown by the curve 32, Fig. 4. In this ligure 33 represents the heat-treating temperature curve, which for each alloy composition is that which permits of the lowest forging temperature, and 34 represents the assumed fusion temperature under ordinary pressure conditions.

After the alloying of the two metals has begun under the pressure induced, amorphous condition herein described, its growth may be fostered in any of the well known mode-s, by hammering, rolling, swaging, or drawing.

Having thus described my invention, what I claim is A' 1. In the process of rendering tungsten ductile, the step of first subjecting a briquet 'of the finely divided metal to a temperature development is secured, 4forging the mass at 20 of about 26000 C. for about ten minutes and the lowestl practicable temperature, and thereafter forging the metal beginning at linally cold working the mass. about 1300 C. and working downwardly 4. The process of alloying tungsten and from the last named temperature. molybdenum which consists in compacting he process of making alloys which togetherunder great pressure a finely 25V consists 1n compacting under' great pressure powdered mixture thereof in the desired prof amixture of the inely divided metals in portions, sintering them for from ten minthe desired proportion, heat-treating the utes and 26000 C. for tungsten to about one mass until al predetermined crystal developminute vand 23000 C. for molybdenum dement is secured. and finally cold Working the pending upon the proportions, forging the 30 mass until themingled amorphoussubstances mass at a temperature' of about 17000 C. are obtained. for an alloy of equal parts downwardly in 3. The process of alloying two crystalline each direction to about 13000 C. for tungsten metals of a highly refractory nature which or about 10000 C. for molybdenum, and

consists in compacting together under great finally cold working the mass. 35

pressure a mixture of the metals reduced to In testimony whereof, I hereunto affix my a very line state of subdivision, heat treating signature.

the mixture until a predetermined crystal FRANK A. F HRENWALD.

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