US2209935A - Alloys and method of making the same - Google Patents

Description

y 30, 1940- M. L. SAM UELS 2,209,935

ALLOYS AND METHOD OF MAKING THE'SAME Filed Sept. 21, 1938 \\\\\\\\\Yi I INVENTOR fi/arf/n L.5amue/5.

4W. ATTORNEYS Patent edJuly so, 1940 UNITED STATES PATENT OFFICE anno s AND tmigg or MAKING THE Martin L. Samueis, Columbus, Ohio, assignor to Battelle Memorial Institute, Columbus,

corporation of Ohio Ohio, a

Application September 21, 1938, Serial No. 231,026

11 Claims.

making the same. It has to do particularly with the making of alloys not hitherto obtainable by melting the constituents thereof together and permitting solidification.

In the prior art, there are certain metals which are insoluble in each other and which, therefore, cannot be alloyed by the usual methods of melting and casting. Thus, it is virtually impossible to obtain anything more than a coarse'mechanical mixture of two metals which are insoluble in the liquid state by ordinary melting processes, and in those cases where a considerable difference in specific gravity exists between the two metals a homogeneous mechanical mixture is not attainable, even when the two liquids are violently agitated and. the mixture is chilled rapidly.

Alloys which are made by powder metallurgy also possess certain drawbacks and limitations. They tend to be somewhat porous. Furthermore,

they are not so ductile as is desirable. Likewise,

because of the high pressures required, the sizes of the articles which may be produced are somewhat limited.

One of the objects of my invention is the making of alloys which cannot be made by the well known methods of melting two or more metals together and permitting solidification.

Another object of my invention is the making characteristics whichare not possessed either by alloys previously produced by melting and solidification or by powder metallurgy.

Another object of my invention is to produce usable and highly desirable alloys from-metals which are wholly or partially insoluble in the molten state.

Still another object of my invention is to pro- ,duce alloys having difierent physical properties 4 and other characteristics from those alloys made either by melting and solidification or by powder metallurgy.

Still another object of my invention is to provide a novel and simple method for producing alloys not obtainable by conventional melting methods and having certain desirable arrangements of the constituents.

I have discovered a novel method whereby homogeneous alloys may be made of metalsor of metals and metalloids that have little alloying tendencies for one another. To prepare such alloys, a suitable parent alloy from materials having limited solubility in the solid state is made. The parent alloy is so chosen that its high meltof alloys which possess certain properties and ing constituent, which separates from the liquid (01. -122) My invention relates to alloys andmethod of on solidification as a network of dendrites, is the high melting point constituent of the resultant alloy, and its temperature range between the solidus and liquidus is fairly wide to insure a reasonable working range of temperatures for subse- 5 quent displacement operations. The parent alloy is then held at a temperature between the liquidus and solidus to liquefy the lower melting point constituent or constituents. As interconnected. channels exist between the solid dendrites, the 10 liquid in the partially melted parent alloy can be displaced by another metallic liquid which usually will constitute the lower melting point constituent of the resultant alloy.

In some cases, where thelower melting point 15 constituent of the resultant alloy cannot directly replace the liquid in the partially melted parent alloy, I have prepared an intermediate alloy by displacement and subsequently 'prepared the resultant-alloy by displacing the liquid portion of 20 the partly liquefied intermediate alloy with the lower melting point constituent of the resultant alloy. For example, when it is desired to substitute tin for the copper in an iron-coppor alloy, the tin cannot be used to force the copper out because at the temperature required to melt the copper, the tin would immediately combine with the iron and would cease to act as an extruding agent before the copper would be forced out. Therefore, lead can be utilized to force the cop- 0 per out, since it has no ailinity for iron and then the temperature can be lowered and tin used to replace the lead. I

Under normal conditions, liquid metal will not drain irom the partially molten parent alloy, per- 3 'haps because of the strong wetting tendencies of the constituents toward each other and because of capillarity, unless differences are set up. These pressure difl'erences can readily be effected if, for example; the molten metal which is to displace the liquid portion of the parent or intermediate alloy is kept on the top side of the parent or intermediate alloy held in a proper fixture, so that the displaced metal can be drawn off at the bottom owing to gravity effects. Additional pressure can be exerted by applying mechanical or gas pressure to the displacing metal or suction to the dischargi side of the said fixture, or by combining pressure and suction.

' When the parent alloy consists of a network of 50 dendriteswith interconnected spaces between the dendrites filled with a lower melting point constituent, heating orholding the allow at a temperature between the liquidus and solidus temperatures permits the displacement of the liquid portion of the alloy with another liquid metallic constituent that is virtually complete. Excess of the displacing constituent can be used to sweep out the last traces of the liquid, lower melting point constituent of the parent alloy so that all which remains is that in solution in the original dendrites.

- Alloys prepared in this manner are unusually sound. Shrinkage areas which may appear in the parent alloy are filled. The completeness of the displacement is remarkable in view of the fact that attempts to drain the lower melting point constituent from the parent alloy with gas pressure or with high-temperature oils failed because of channeling, the gas or oil passing through the channels without removing the metallic liquid from the regions surrounding the channels through which the gas or oil flowed. Success of my displacement method of preparing alloys seems to depend partly upon the wetting characteristics of the liquid displacing constituent toward the solid dendrites.

The displacing constituent which I utilize is preferably a metal which is substantially insoluble in the high melting point constituent at the temperatures of the displacing metal during the displacing action. Likewise, there is an upper and lower limit to the amount of metal to be displaced, since if the percentage thereof is too small,

the channels between the dendrites of the high melting point constituent will be inadequate to permit effective displacement and if the percentage thereof is too large, the dendritic structure will not have sufficient strength to retain its shape during the displacing operation.

The completeness of the displacement is illustrated from the following information on compositions of various parent alloys used and of the resultant alloys:

Parent alloy, approx- Displacegg gg Chemical compoimate composition mer t tempera? sition of result- (by weight) liquid 0 ant alloy ture, F.

50% Cl1-50% Fe.-. Lead 2050-2100 41.12??? 5e, 33.95%

, u. 50% Cu-50% Fe"-.. Silver"... 2050-2100 4313491; Fe, C51.46%

g, .3 u. 55% Cir-% Bi... Lead 760-800 55.76% C-u, 44.37% Pb, less than- .10% Hi. FBAls-Al do... 1300 FeAla plus Pb (percentages not determined). Ou50% Fe"... Magne- 2050-2100 Fe plus Mg (persium centages not determined). (By volume) (By difference) 50% Ill-50% Sn Lead 670 77.64% Pb, 0.08%

Sn, 22% Al.

The limitations on the displacing constituent are principally that its melting point be below the melting point of the dendrites in the parent alloy and that it have little tendency to alloy with the solid dendrites during the length of time at the temperature required to complete displacement.

The applications of my process are numerous, as will be seen from the following descriptions.

Molten aluminum has little or no afiinity for molten lead, so that a liquid solution or chemical combination between the two metals cannot be obtained. When the two metals, in molten form, are stirred together, due to the molten aluminum having a specific gravity of only 2.3 while the specific gravity of molten lead is approximately H, the lead settles rapidly to the bottom of the mold, and upon complete solidification two solid layers are found, one consisting almost entirely of aluminum and the other consisting almost entirely of lead.

Aluminum and tin are completely soluble in the liquid state and only slightly soluble in the solid state. When aluminum and tin are heated together to a temperature higher than the melting point, a uniform homogeneous liquid solution is obtained. Upon cooling, dendrites of aluminum carrying a very small amount of tin in solid solution are formed with the major portion of the tin remaining liquid and constituting the filling of inter-dendritic material. It thus happens that in an aluminum-tin alloy composed of equal parts of each metal, the major portion of the aluminum freezes at a temperature of approximately 610 C., while the major portion of the tin does not freeze until a temperature of 230 C. is reached. Due to the two metals being completely soluble in the liquid state, no separation or liquation takes place, and a high degree of uniformity as regards the distribution of the two constituents is obtained upon complete solidification.

The tin in the above-mentioned alloy can subsequently be displaced with liquid lead so that the distribution of the lead in the new aluminumlead alloy is determined by the distribution of tin in the parent aluminum-tin alloy and not upon the characteristics of the aluminum-lead system. The parent specimen of aluminum-tin is heated to a temperature high enough to melt the tin but not high enough to cause the aluminum dendrites to melt, 350 C. for example. Molten lead in a chamber disposed above the specimen exerts pressure thereon and causes the liquid tin to be exuded at the bottom, and the lead comes into the interdendritic interstices and takes the place of the tin. A small head of lead suflices to cause fairly rapid dripping, but this rate can be increased by applying pressure from an air line or a nitrogen tank.

In the accompanying drawing:

Figure 1 is a vertical sectional view of apparatus which I may use in my process.

Figure 2 is a photomicrograph of a parent alloy of copper and silver.

Figure 3 is a photomicrograph of an alloy made from the alloy of Figure 2 by displacing the low melting point constituent with lead.'

Figure 4 is a photomicrograph of a parent alloy of copper and bismuth.

Figure 5 is a photomicrograph of an alloy produced from the alloy of Figure 4 by displacing the bismuth with molten lead.

Figure 1 shows an apparatus which is suitable for carrying out the displacement process. The specimen consisting of the parent alloy is machined round and with a slight taper and fitted as a male part intoa holder having the same taper which acts as a female part. The holder carrying the dendritic specimen is attached to a pipe by means of a coupling and the metal which is .to serve as the displacing material is placed in the pipe container above the specimen. The assembly is then lowered into a vertical furnace, preferably of the tube type, and brought up to a temperature at which both the interdendritic filling material in the specimen and the displacing metal above are fully molten. At this time the head of displacing metal forces the liquid interdendritic material to exude from the bottom of the specimen.

Other methods, however, can be used to carry out the displacement. For example, the parent alloy can be held in the furnace in which it is made or be cast into a refractory or metal form which can also hold the displacing metal. By holding the parent metal at the proper temperature in either the furnace or the form, the lower melting point constituent can be forced out of the space it occupied by the displacing metal. The above examples, simply serve as illustrations of the displacement processes which can be applied to many alloy systems.

The following table lists a number of alloys, but in no way does it exhaust all the possibilities, for there are not only other binary but ternary and morev complex alloys that canbe made by my displacement process.

has displaced the copper-silver eutectic is represented by the white areas.

Nickel and silver have so little affinity for each other that no alloys have been made by conventional melting methods, and the term nickelsilver" has been applied to alloys of nickel, copper andzinc in which no silver is present. By the use of my displacement process, an actual alloy of nickel and silver has been made. Some have questioned whether or not the term alloy should be applied to such systems as the iron-silver and nickel-silver combinations, which show very little Possible parent Lower melting Displacing constitalloy constituent uent Resultant alloy Iron-copper Iron-silver.

Do Iron-bismuth.

Iron-barium.

Iron-calcium.

Iron-tin.

Lead First lead, then tin. Thallium Beryllium-alumin- Aluminum.

Iron-silv Iron-magnesium. Iron-strontium. Iron-lead.

Nickel -silver.

el-lead.

. Nickel-tin.

Nickel-thallium. Aluminum-bismuth. Aluminum-cadmium. Aluminumotassium. Aluminumead. Aluminum-thallium. Cadmium-gallium. Copper-lead. Copper-selenium. Copper-tellurmm. Copper-thallium.

' Copper-tin (no compounds).

Silicon-lead.

Silicon-thallium.

. Silver-selenium.

Beryllium-magnesium.

Nickel-lead. Iron-lead. Nickel-silver.

Figure 2 of the drawing is a photomicrograph at a magnification of 100 diameters showing the structure of a parent alloy of copper-silver containing 70 per cent of copper and 30 per cent of silver. In this structure, the high melting con- 'stituent is in the form of dendrites and consists of copper with a small amount of silver in solid solution. The white or inter-dendritic material consists of a eutectic which is made up of the silver-rich and the copper-rich solid solutiyns. The

copper-rich dendrites melt at a'temperature only slightly below the melting point of pure copper (1083 C.), but the eutectic filling material melts at approximately 780 0.; hence by heating to 800 C. the eutectic or filling constituentis made fully molten, but the dendrites are still solid and, having an interlocking structure; possess enough strength to hold the specimen in shape. Molten solubility even in the liquid state. One definition of the term alloy has been given as follows:

"An alloy is an association of some intimacy,

of two or more metals, or of one or more metals with one or more non-metals.

In making silver-nickel alloy bymy method, a parent alloy of nickel and bismuth is made up, and the bismuth is subsequently displaced by molten silver. It is found that the silver-nickel alloy" made by my displacement process has the same intimacy of association of the two metals as does the parent metal of bismuth-nickel, which is admittedly a true alloy.

Ina' like manner, iron-silver alloys have .been made by-the use of an iron-copper parent alloy in which, the copperfilling material is displaced with silver. Iron and silver are frequently cited as an example of a binary system in which the two component metals are entirely insoluble,

both in the liquid and solid states, since silver may be melted in an iron crucible without. contamination. Through the useof the displacement process, I obtain, however, an iron-silver -alloypossessing the same intimacy of contact 01' the two metals that a similar composition does in the iron-copper system.. The effect on the physical properties of displacing the copper in a. 50-50 copper-iron alloy with silver was as follows:

' 5 Percent Sample Approximate f gz 3:23;? elongpagg Brinell No. composition Ill/5min no?!1 m 0.1 g hardn f 1A Fe-Ou(5050). 53,500 r 65,000 22.5 31.3 121 2-13 Fe-Ag(50-50) 33,000 44,200 41.0 74.5 78

The results of these comparative tests show that substitution of the silver for the copper has resulted in markedly improved ductility.

Producers of copper-lead bearings have long been troubled by a separation of the copper-rich and the lead-rich phases prior to complete solidi iication due to two separate liquid solutions forming when high lead contents are used. This difficulty is eliminated by making a parent alloy of copper and bismuth, in which there is complete liquid miscibility, and subsequently displacing the bismuth with lead. Figure 4 illustrates the structure of the parent alloy in which the copper dendrites constitute the high melting phase and the bismuth inter-dendritic fillings represent the low melting constituent. By heating to a temperature of 350 C., the bismuth fillings are fully muth alloy may contain as much as 50 per cent of bismuth, after displacement the bismuth content has been found to run less than 0.10 per cent. By this method it has beenpossible to make alloys containing as low as 15 per cent lead and as high as 70 per cent lead, the remainder being copper except for a few hundredths of a per cent of residual bismuth.

It the bismuth m the parent copper-bismuth alloy is displaced with molten tin, care being used to heat to no higher temperature than is required to melt the bismuth, an alloy is obtained in which the' copper is present as dendrites and the tin occupies inter-dendritic areas without appreciable alloying or compound formation between the copper and tin. Displacement has been the molten tin was poured into the displacement chamber until the specimen with its container was quenched in water. A 40-60 tin-copper alloy made in this manner showed a hardness of only 31, Rockwell B in the as-displaced". condition, while upon heating to 900 F. and holding for 1 hour the hardness went up to 95 Rockwell B. Conventional melting methods cannot help but produce hard and brittle copper-tin compounds with a similar composition, whereas here the tin is introduced at a temperature so low that the reaction is not rapid, and compound formation is further reduced by holding the time dur- ,the direction of drawings.

In alloys made by the displacement process, the displacing metal is always the continuous phase, surrounding the dendrites of the higher melting constituent. This point may be used to advantage in the making of electrical contacts. Upon forging and drawing the 50-50 silver-nickel alloy into wire, it was found that the nickel and silver weredrawn out into stringers parallel with Subsequent annealing caused-both the nickel and silver to recrystallize and soften but did not change the relative position of the two metals, since they are insoluble in each other.

The specific examples of the use of the displacement process described above are not meant to set up limits. The process herein described is applicable to many other binary as well as ternary and more complex alloy systems in which there is a fairly wide temperature interval between the liquidus and they solidus. By heating any such alloy to a temperature at which the low melting constituent becomes fluid but at which the high melting dendrites are solid, another molten metal can be forced in to take the place of the low melting phase. Definite examples have only been given in an effort to clarify the principles involved in the process.

It will be seen from the above that I have provided a type of alloy which is distinctly novel in several respects. In the first place, I have been able to produce, for the first time, an alloy of two or more metals having. a microstructure which is difierent in character from the microstructure resulting from the production of a similar alloy either by melting and solidification or by powder metallurgy. For example, in the use of a parent alloy of iron and copper, the replacement of the copper by lead to form an intermediate alloy and the subsequent replacement of the lead by tin to forms. final alloy of iron and tin, I produce an alloy wherein the micr0structure is more similar to the iron-copper alloy than it is to the iron-tin alloy which could be formed made in 80 seconds, counting the time from which ing which the copper and molten tin are in conable range oftemperature between the melting points of the two metals. This fact is proven by the production of the copper-tin alloy described above in which the two metals combine with each other with great rapidity at high temperatures.

by melting and solidification'or by powder metale lurgy. In other words, in this particular case, the dendritic structure which is mainly iron re mains substantially unchanged from the form which it assumes in the preparation of the ironcopper alloy, so that the final introduction of tin into the interstices between the iron dendrites produces an alloy of a totally different microstructure than would have resulted from melting and solidification or from powder metallurgy.

Thus, it is a distinctly novel characteristic of my invention that I am able to produce an alloy of two or more metals having a mic-restructure which is distinctlydifi'erent in character fromv the microstructure of previously known alloys of the same metals.

In addition to the above, a distinct advantage ofmy method is that I am able to produce an alloy of two or more metals wherein the physical properties of the alloy are distinctly different from the physical properties of a substantially.

similar alloy made by melting and solidification or by powder metallurgy. This is clearly indicated by the fact that a 40-60 tin-copper alloy made in accordance with my invention showed a hardness of only 31 Rockwell B in the 'asdisplaced" condition whereas, upon heating to 900 F. and holding for an hour, the hardness went up to 95Rockwell B. Obviously, this heat treatment tends to simulate the conditions that would result from the formation of the same al- 10y by melting and solidification. Thus, it will the displacement of the liquid metal of the parent be seen that it is possible by the use of my process to produce a tin-copper alloy considerably softer than would be possible by producing the same alloy by melting and solidification". As indicated above, such an alloy with its compara-:

of alloys with other improved characteristics j such as electrical and thermal conductivity. Indications are that my method also makes possible the formation of alloys of two or more metals having physical properties which are dis-' tinctly diflferent from the physical properties of a similar alloy produced by powder metallurgy. Obviously, the formation of the dendritic structure of the high melting point constituent and.

the retention of this dendritic structure even after the final alloy is formed will result in increased ductility of the alloy in comparison with an alloy of similar chemical composition produced by powder metallurgy since such an alloy cannot have this dendritic structure.

In the production of an alloy by powder metallurgy, the high pressures required to make a satisfactory alloy places a severe limitation on the sizes and shapes of the alloys which can be produced. No such limitation exists with my process or, at least, if they do exist, they are not nearly so severe.

Even more important man the above advantages is the fact that I am able to produce alloys of metals previously unobtainable by conventional melting methods. It is well known that alloys of certain of these metals are desirable but their lack of aflinity for each other has hitherto made it impossible to produce such alloys by melting and solidification. v

Various other advantages of my invention will appear from the above description and the appended claims.

7 Having thus describedclaim is:

1. A process for making an alloy of two or more metals which are immiscible in the liquid state which comprises heating an alloy with -a low melting point constituent and a high melting point constitutent of dendritic form to render' the low melting point constituent molten and then replacing the low melting point constituent with a constituent which is immiscible with the high melting point constituent in.a liquid state.

2. -A process for making alloys of compoundforming metals having substantial differences in melting temperatures without forming componds, comprising the selection or preparation of a parent alloy of non-compound forming metals having a wide range of temperature between the solidus and liquidus'and having as its highest melting point constituent the highest melting point constituent of theresultant alloy in dendritic form; the holding of the parent alloy at a temperature between the solidus and liquidus temperatures and at such a temperature that compound formation between constituents of the resultant alloy is prevented to efi'ect the melting of the lower melting point constituent of the parent alloy not wanted in the resultant alloy;

my invention, what I alloy with liquid metal which forms no compounds with the solid metal ofthe parent alloy .and which has a melting temperature either lower or only slightly in excess of the lower melting point constituent of the resultant alloy; the regulating of the temperature of the intermediate alloy to a temperature above the melting temperature of both the non-compound forming low melting point metallic constituent and of intermediate alloy and the lower melting point constituent of the resultant alloy but below'the temperature at which compound formation is rapidly initiated; the displacement ofthe liquid noncompound forming metallic constituent in the intermediate alloy with a liquid, lower melting point constituent of the resultant alloy; and the rapid solidification of the resultant alloy. I

3. A process for making alloys of metals comprising theselection or preparation of a parent alloy of dendritic structure having a wide range of temperature between the solidus and liquidus, the holding of this alloy 'at a temperature between the solidus and liquidus temperatures to efiect partial melting of the alloy, the displacement of the. liquid portion of the alloy with another liquid metallic constituent whose melting temperature is below the liquidus temperature of the parent alloy to form an intermediate alloy, the holding of the intermediate alloy at a temperature at which both themetal replacing the lower melting point constituent of the parent" alloy and the lower melting point constituent of the resultant alloy is liquid, the displacement of the liquid metal of the intermediate alloy with the lower melting point constituent of theresultant alloy, and the solidification of the resultant alloy. 4. A process for making alloys of metals, said process comprising the selection or preparation of a parent alloy of dendritic structure having a wide range of temperature between the solidus and liquidus and having as-the high melting point constituent the high melting point constituent of the resultant alloy, the displacement of the low melting point constituent of the parent alloy at a temperature at which the .alloy is partially liquid with another liquid metallic constituent which forms the lower melting point con-' another in the solid state, said constituents hav-' ing difierent melting points with the higher melting point constituent being a'high melting point constituent of the resultant alloy, the. displacement of the lower melting point constituent of the parent alloy at a temperature at which it is liquid by another liquid metallicconstituent which forms the lower melting point constituent of the resultant alloy, and the solidification of the resultant alloy.

6. A process for making alloys of metals possessing marked affinity for each other in the solid as well as the liquid states without permitting much reaction or solution, comprising the selection or preparation of aparent alloy of dendritic structure having a wide range of temperatures between the solidus and liquidus and having as its highest melting point constituent, the highest melting point constituent of the resultant alloy,

between the solidus and liquidus temperatures to effect the melting of the lower melting point constituents of the parent alloy not wanted in the resultant alloy, the displacement of the liquid metal of the parent alloy with liquid metal constituting the lower melting point constituent of the resultant alloy at such a rapid rate that reaction or solution between the high melting point constituent and the displacing liquid metal is not materially efiected, and then fiecting the rapid solidification of the resultant a 0y.

'7. A process for making an alloy of two or more metals which comprises heating an alloy having a low melting point constituent and a high melting point constituent of dendritic form to render the low melting point constituent molten and replacing the said low melting point constituent with a difierent low melting point metallic constituent in molten form, and solidifying of the resultant alloy.

8. The process of claim '7, wherein the said low melting point constituent of the original alloy is displaced by the action of a force on a molten bath of the low melting point constituent of the resultant alloy.

9. An alloy of two or more metals comprising a low melting point constituent; and a high melting point constituent of dendritic form, said alloy being made by heating a parent alloy having a low melting point constituent and a high melting point constituent of dendritic form to melt the low melting point constituent thereof, replacing the molten constituent with a different low melting point metallic constituent -in molten form, and solidifying the resultant alloy.

10. The alloy of claim 9, wherein neither the low melting point constituent nor the high melting point constituent of the final alloy is completely soluble in the other said constituent in the liquid state.

11. The alloy of claim 9, wherein the low melting point constituent and the high melting point constituent of the final alloy are at least partially mutually soluble in the solid state, but are present in forms substantially free from mutual solution;-

MARTDT L. SAMUELS.

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