US3082521A - Beryllium alloy and method of making the same - Google Patents

Description

March 26, 1963 v J. B. COHEN 3,

BERYLLIUM ALLOY AND METHOD OF MAKING THE SAME Filed Jan. 19, 1959 F 1 WEIGHT PER CENT BERYLLIUM Bi 05: L52 3 4 5 7.5 lb 20 30 I300 TEMPERATURE 0 IO 20 3O 4O 5O 6O 7O 8O 90 I00 ATOMIC PER CENT BERYLLIUM JEROME B. COHEN INVENTOR.

ATTORNEYS United States Patent Gdice Patented i viai. 26, 1953 3,532,521 BERYLLEUM ALLOY AND METHGB flit MAKEN'G THE SAME Jerome B. Cohen, Arlington, Muse, assignor to Aveo Manufacturing Corporation, Cincinnati, @hio, a corporation of Delaware Filed .i'an. 19, 1959, Set. N 7 87,491 2 {*Ci. 29-497) The present invention relates to an alloy of beryllium and more particularly to a binary alloy of beryllium and silver, and to a unique method of producing the alloy and rendering it ductile.

The quest for ductile beryllium has been going on for many years. The search has recently been accelerated by the attractive properties of beryllium for missile applications. Not only is the material light in weight (atomic weight of approximately 9) but it also has high strength at high temperature.

Early investigators soon found that pure beryllium is exceedingly brittle and turned attention to alloys of the metal that they thought would be ductile and would retain at least some of the desirable attributes of pure beryllium. Early patents relating to such alloys are 1,868,293; 1,905,312; and 1,905,313. The latter patent teaches that an alloy including approximately 70% beryllium and 38% aluminum overcomes the inherent brittleness of the beryllium and makes possible mechanical operations such as rolling and forging.

Despite favorable reports of early researchers in the field, the alloys of beryllium and aluminum are lacking in both strength and ductility. As recently as 1955, the American Society for Metals published a text entitled The Metal Beryllium edited by D. W. White, Jr. and

I. E. Burke, which states: One can imagine that the brittleness of beryllium can be partially overcome by pre paring an alloy in which small beryllium grains are completely surrounded by a matrix of ductle metal. The most obvious possibility is an alloy of beryllium and aluminum since no compounds are formed in this system. Several studies of such alloys have been reported it seems sufiicient merely to say of these results that none of the alloys bet- ween 10 and 70% beryllium appeared to be outstanding in strength or ductility (page 567).

Attention has also been directed in the past to binary alloys of silver and beryllium. Although various alloys have been explored extensively and the constitution dia gram of the binary alloy system has been fairly well established, researchers have failed to report the development of a ductile form of the alloy. To the contrary, an article by H. A. Slomau, Alloys of Silver and Beryllium, ap pea-ring in volume 54 of the 1934 Journal of the Institute of Metals, reports that alloys containing more than 90% by weight of silver and from 3 to 5% by weight of beryllium, although resistant to corrosive attack by sulphur, are brittle in the chill-cast state. A similar statement appears in the Cooper Patent 1,816,961 (1931) relating to a silver beryllium alloy.

Contrary to such early reports, alloys of silver and beryllium can be made ductile if produced by the novel process to be described. Briefly, the invention comprises the production of a metastable form of the alloy in which the beryllium is present as discrete globules surrounded by a matrix of substantially pure silver. The metastable form of the alloy is made by quickly cooling it through the temperature range in which peritectic phases tend to form under conditions of temperature equilibrium. In other words, it has been found by actual laboratory experiments that chill casting of alloys having a high beryllium content yields a ductile material, a discovery that is diametrically opposed to the teaching of the prior art.

In view of the foregoing, it will be understood that an important object of the invention is to provide a ductile alloy of silver and beryllium.

it is also an object of the invention to provide a method of producing a ductile alloy of beryllium and silver.

A further object of the invention is the provision of a method of producing a ductile alloy of beryllium by cooling the alloy from a liquid state at a rate sufiiciently fast to avoid formation of intermediate phases.

A still further object of the invention is the provision of a method of producing a metastable alloy of silver and beryllium which, upon reheating, will convert in part to a stable peritectic constituent yielding a heterogeneous solid having a higher melting temperature than that of the metastable material.

A specific object of the invention is the provision of a ductile binary alloy of beryllium and silver, and the meth- 0d of producing the same, in which the weight percent of beryllium exceeds 18.5% of the alloy.

The novel features that ii consider characteristic of my invention are set forth in the appended claims; the inven tion itself, however, both as to its composition and method of manufacture, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in conjunction with the accompanying-drawings, in which:

FiGURE 1 is a constitution diagram for binary alloys of beryllium and silver;

FIGURE 2 is a photomicro-graph of a metastable alloy of 16.9 atomic percent silver in beryllium;

FIGURE 3 is a photomicrograph of an alloy of 14.3 atomic percent silver in beryllium showing the formation of the 5 peritectic phase within a silver matrix;

FIGURE 4. is a photornicrograph of any alloy of 18.6 atomic percent silver in beryllium after cold rolling; and

FIGURE 5 is a photomicrograph of an alloy of 14.3 atomic percent silver in beryllium indicating the effect of the 6. peritectic phase on ductility.

Attention is first directed to FlGURE 1 showing the constitution diagram for silver-beryllium alloys. As is conventional, the diagram shows the weight percent and atomic percent of beryllium-silver alloys vs. temperature and shows the various solid phases that form at equilibrium temperatures over extended time periods. For background purposes, it will first be assumed that a conventional binary alloy of 30 atomic percent beryllium and silver is to be formed. Those skilled in the art will understand that a homogeneous liquid solution of the beryllium and silver exists above 1109 C., as indicated by the liquidus line 1. As slow cooling occurs below 1100" C., practically pure beryllium begins to precipitate as a primary phase. As this occurs, the concentration of silver in the'rernaining liquid gradually increases. At 1010" C., the liquid attacks the primary beryllium phase and converts to the 6 peritectic phase. solidification occurs at I'll-10 C. and, below 1910" C. and above .850 C., the alloy is a mixture of a beryllium solid solution and the 6 phase.

During cooling below 350 C., conversion of the 5 phase to the 7 phase occurs, followed at 760 C., the eutectoid temperature, by the formation of a mechanical mixture of the primary beryllium-rich and silver-rich solid solutions. For practical purposes, the solid solutions can be regarded as comprising a, heterogeneous solution of the silver and beryllium.

The .6 peritectic phase, although possessed of high strength, is very brittle and, when present in a binary alloy of silver and beryllium in any significant quantity, renders the material too brittle to permit any significant amount of rolling or forging.

It has been found, however, that the formation of the imparted to the alloy if it is rapidly cooled from a temperature above the liquidus to room temperature. This is possible because peritectic transformations are quite slow.

Attention should now be directed to FIGURE 2 which shows a photomicrograph (500 magnifications) of an alloy of 16.9 atomic percent silver in beryllium after being etched by a dilute solution of ammonium hydroxide and hydrogen peroxide. The shaded areas 2 are primary phase beryllium globules precipitated out of the homogeneous liquid solution during the early stages of cooling. The light area 3, surrounding the beryllium globules, is predominantly silver and provides a ductile matrix. The exact rate of cooling is a function of the mass of the material being cast, as well as that of the furnace, and ambient temperature conditions. The rate of cooling must, however, be sutficiently rapid to avoid the formation of the 6 and 7 phases. Failure of early researchers to recognize the importance of rapid cooling led to their failure to develop a ductile beryllium alloy. In the past, some ductility has been attained by prolonged heat treatment below the 760 C. eutectoid temperature; this, however, is not regarded as a practical approach to the problem.

FIGURE 3 shows the appearance of a 14.3 atomic percent silver-beryllium alloy, etched as before, as it appears at 500 magnifications. In this case the shaded areas 4 are beryllium globules and, as before, the white areas 5 are silver. Adjacent the globules, however, is an intermediate area 6 of the 6 phase. These areas are relatively angular and at their sharp projections and re-entrant angles set up stress risers which encourage fracture of the material when it is stressed, as during rolling. The presence of the 6 phase clearly indicates that the material has not been cooled at a sufficiently rapid rate, and the resulting material is very brittle. In practice, the proper cooling rate can readily be determined under any given circumstances by checking the resulting product for the presence of the 6 phase. When 'it is absent, as indicated by FIGURE 2, the cooling rate has been sufiiciently high and the resulting material will be ductile and malleable.

FIGURE 4 shows the appearance of an alloy of 18.6 atomic percent silver in beryllium after an 83% reduction in thickness .by cold rolling at room temperature. It will be noted that the primary beryllium phase 7 is still surrounded by the ductile silver matrix S and that elongation of the primary phase globules has occurred without fracture of the matrix. This figure is to be contrasted with FIGURE 5 which shows the effects of cold rolling a specimen of the material in which some 6 phase transformation has occurred. In the upper portionof the figure plastic flow has occurred. The primary beryllium phase 9 is elongated and still surrounded by the ductile silver matrix 10. At the lower portion of the figure, however, the 6 phase 11 is in evidence. Fracture of this phase is apparent at 12 and it will be noted that the primary phase beryllium globules have not elongated but have been held in their original shape by the surrounding brittle 6 phase.

Although formation of a comparatively stable metastable mixture of the beryllium primary phase in a silver matrix is theoretically possible at any beryllium concentration higher than that of the eutectic 0.5 atomic percent beryllium), any large proportion of silver so increases the weight of the resulting material as to defeat in large measure the advantages of using lightweight beryllium. It is considered more advantageous to form the novel material of the invention at beryllium concentrations equal to or greater than that at which the 5 phase forms, i.e., approximately 8.5 weight percent beryllium.

An advantage of under cooling to form the metastable mixture shown in FIGURE 2 is the increase of tempera- 4 ture at which liquid forms upon reheating. This is of significant value if the material is used in the formation of welding or brazing material for joining beryllium parts. For such applications, ductility is highly desirable to permit formation of rod and sheet stock. Such material in use is heated above880 C. where melting occurs. At temperatures in excess of 850 C., the 5 phase gradually forms in the material that has been deposited in the joint. The 5 formation is not objectionable under such conditions and, in fact, is desirable from the standpoint of the increased strength due to the 6 phase. Further, after transformation of the 6 phase, the initial melting point of the alloy increases from approximately 880 C. to 1010 C. This is highly significant in effectively raising the melting point of the joint above the temperature at which the material originally melted, resulting in increased hot strength of the joint.

In carrying out the process of this invention, conventional equipment and techniques may be employed. Melting of the constituents may be eifected in an electric furnace, using either an alumina or a beryllia crucible. Melting may be carried out at about 1300 C. in a vacuum or in an inert atmosphere, such as argon gas at 400-800 microns pressure. Cooling of the melt may be eifected by water coils surrounding the crucible and is carried on at a rate suificient to prevent formation of the 6 phase as has been explained.

The constituents may be placed in the crucible in lump form and do not require any special mechanical preparation.

Because of the tendency of beryllium to vaporize, it is advisable to add approximately 1% additional beryllium to any'alloy being made, particularly if heating is carried out in a vacuum. Loss by vaporization can be reduced somewhat by heating in an atmosphere under pressure.

The elements used in making the alloys shown in the attached figures were commercially available grades of beryllium and silver. The beryllium was 99.2% pure, the principal impurities being BeO, Be C, Fe, Al. The silver was 99.99% pure having as its principal impurities Fe, Pb, Si, Mg.

The density of the resulting alloy depends in large measure upon the silver content. For an alloy having 18.6 atomic percent silver, the density is 4.5, whereas for a 14.3 atomic percent alloy, the density is 3.9. These values indicate that a ductile beryllium alloy can be produced which is 40% less dense than steel.

The macrohardness of the resulting alloys is essentially determined by the hardness of the particles of the primary beryllium phase in the cast ingots, which are softer than pure beryllium. Referring to Vickers hardness readings with a 1000 gram load, the hardness of beryllium is 269, and of silver is 92. An alloy having 14.3 atomic percent silver has a hardness of 117. It was found that silver beryllium alloys have a slight tendency toward work hardening during cold rolling, attaining a Vickers (1000 g. load) hardness reading of about 150.

The availability of a ductile beryllium alloy is of great importance at this time for use in missile and advanced aircraft programs. The novel alloy set forth herein not only has many of the beneficial attributes of beryllium but is also characterized by ductility and mechanical workability and is expected to find many applications in joining other alloys and pure beryllium.

The various features and advantages of the invention are thought to be clear from the foregoing description. Others not specifically enumerated will undoubtedly occur to those versed in the art, all of which may be achieved without departing from the spirit and scope of the invention as defined by the following claims.

I claim:

1. The method of producing a temperature-resistant joint from a beryllium-silver alloy which comprises heating the constituents above the liquids to form a ho mogeneous liquid solution, cooling the alloy at a controlled rate whereby primary beryllium globules are formed in a silver matrix, reheating the alloy to a temperature above the eutectic temperature to liquify the alloy for making the joint, holding the alloy above the temperature at which peritectic transformation begins, and cooling the alloy with the peritectic phase retained.

2. The method of producing a temperature-resistant joint from a beryllium-silver alloy which comprises heating the constituents above the liquidus to form a homogeneous liquid solution, cooling the alloy at a controlled rate whereby primary beryllium globules are formed in a silver matrix, reheating the alloy above 800 C. to liquify the alloy for making a joint, holding the alloy above 850 C. for inducing peritectic transforma- 6 tion, and cooling the alloy with the peritectiv phase retained.

References Cited in the file of this patent UNITED STATES PATENTS 2,048,706 Pfanstiehl July 28, 1936 2,272,063 Hensel et al. Feb. 3, 1942 2,539,298 Doty et al. Jan. 23, 1951 OTHER REFERENCES Metals and Alloys, July, 1941, pages 37 to 39. Published by Reinhold Publishing Company, East Stroudsburg, Pa.

Constitution of Binary Alloys, Metallurgy and Metallurgical Engineering Series, 2nd edition, pages 9 and 10. Edited by Hansen. Published in 1958 by the McGraw- Hill Book Company, New York.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Jerome B. Cohen numbered patror appears in the above d as certified that er he said Letters Patent should rea It is hereby nd that 1;

ant requiring correction a corrected below.

Column 1, line 38, for "ductle" read ductile column 2, line 34, for "any" read an column 5, line 2, for "liquids" read liquidus line 14, for "800" read 880 read peritectic line 1, for "peritectiv column 6,

(1 this 12th day of November 1963.

Signed and seale (SEAL) Attest:

EDWIN L. REYNOLDS ERNEST W. SWIDER A ting Commissioner of Patents Attesting Officer

Claims (1)

1. THE METHOD OF PRODUCING A TEMPERATURE-RESISTANT JOINT FROM A BERYLLIUM-SILVER ALLOY WHICH COMPRISES HEATING THE CONSTITUENTS ABOVE THE LIQUIDS TO FORM A HOMOGENEOUS LIQUID SOLUTION, COOLING THE ALLOY AT A CON-

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