US3380813A - Composites of beryllium-copper-tin - Google Patents

Description

United States Patent 3,380,813 COMPOSITES OF BERYLLIUM-COPPER-TIN Earl I. Larsen, Indianapolis, Ind., and Richard H. Krock,

Peabody, and Clintford R. Jones, Arlington, Mass., as-

signors to P. R. Mallory & Co. Inc., Indianapolis, Ind.,

a corporation of Delaware Filed May 22, 1967, Ser. No. 640,193 4 Claims. (Cl. 29182.1)

ABSTRACT OF THE DISCLOSURE A two-phase composite material whose microstructure consists of beryllium dispersed in a copper-tin-beryllium solid solution alloy matrix was produced by liquid phase sintering pressed powder mixtures of beryllium, copper and tin or powder mixtures of beryllium and prealloyed copper-tin.

The present invention relates to ductile composites of beryllium-copper-tin which can be sintered to substantially theoretical density and to means and methods for providing said composites through liquid phase sintering.

Liquid phase sintering differs from the several other types of sintering techniques in that the sintering of the compact is carried out in the presence of a liquid phase. Liquid phase sintering encompasses raising the temperature of the compressed powder metal constituents of beryllium, copper and tin to a temperature wherein a predetermined amount of the liquid phase appears. In the liquid phase, one of the metal constituents, the solid, is progressively dissolved in the other metal constituent or constituents, the liquid. However, the quantities of these constituents are such that, at equilibrium, some solid phase always exists. It is thought that the liquid wets the solid so as to bring about favorable surface energies existing between the liquid and the solid thereby permitting solution into the liquid phase.

However, heretofore, when beryllium-copper-tin composites were fabricated in accordance with known liquid phase sintering techniques, it was found that the solid beryllium expelled the liquid copper-tin-beryllium alloy from the compact during liquid phase sintering. It is thought that the unfavorable surface energy equilibrium causing expulsion of the liquid copper-tin-beryllium alloy is due to a tough, tenacious film of beryllium oxide which is present on each particle of beryllium.

The present invention prevents the expulsion of the liquid copper-tin-beryllium alloy from the specimen by using an agency to intervene in the sintering stage. The agency either breaks down the oxide film on the beryllium or segregates to the metal oxide interface and lowers the surface energy of the liquid metal with respect to the beryllium oxide film so that the liquid metal progressively dissolves the solid metal.

The agency can be called a fluxing agent or flux, however, the agent has other characteristics which assist in wetting beryllium so as to surround the beryllium with a ductile envelope phase of copper-tin-beryllium alloy matrix metal thereby avoiding the expulsion of the liquid from the specimen.

Beryllium has several desirable physical features which make it attractive for a variety of commercial applications such as lightweight gears, lightweight fasteners, gimbals, brackets, housing, airplane parts or the like. However, beryllium has one major drawback which has seriously limited its commercial acceptance, that is, beryllium is inherently brittle at room temperature.

The lack of ductility of beryllium is attributed to the crystal structure of beryllium which is hexagonal close packed. During deformation, the basal planes of the hexagonal close packed structure, being the easiest to slip, are aligned along the working direction. Since slip is crystallographically difiicult perpendicular to the basal plane, the ductility of beryllium perpendicular to the primary fabrication direction is practically nonexistent.

Several possible solutions have been advanced in an attempt to make beryllium metal sufficiently ductile so as to permit a widespread commercial acceptance of beryllium. Cross-rolling and cross-forging have been suggested as fabrication methods which might enhance the ductility of beryllium. These fabrication techniques reduced the number of basal planes along the direction of rolling and resulted in improved ductility. However, the degree of improvement was far from satisfactory. The fact remained that beryllium must be classified as brittle at room temperature even utilizing the aforementioned method when ductility perpendicular to the fabrication temperature is considered. In addition, the abovementioned technique would not be feasible where the fabrication is, by nature, solely along one axis such as swaging, drawing and extrusion.

In recent years, attention has been directed to the fabrication of beryllium alloys not having the inherent brittleness of beryllium itself but possessing various outstanding properties of the metal such as, for example, low density combined with high strength. It is thought that US. Patent 3,082,521 fabricated the first ductile beryllium alloy by rapidly cooling the part from a temperature at which it was liquid. However, the beryllium content of the alloy was not in excess of 86.3 atomic percent which is approximately 33 weight percent of the alloy. Although the beryllium alloy was ductile, the density of the alloy was in excess of that of aluminum and about equal to that of titanium.

It has also been suggested that beryllium alloys might be fabricated by pressing and sintering a mix of metal powders. However, such a method results in expulsion of the matrix metal or metals from the beryllium specimen and the eventual freezing of the matrix metal or metals into globs on the surface of the solid specimen. It is thought that the expulsion of the matrix metal or metals is due to the surface energies of the solid beryllium and the various liquids formed. The unfavorable surface energy equilibrium is believed to be due to a tough, tenacious film of beryllium oxide which is present on each particle of beryllium.

A means and method have been discovered for preparing a composite of beryllium, copper and tin containing about 50 to percent, by weight, of beryllium, about 13.3 to about 50 percent, by weight, copper and a trace to about 5.5 percent, by weight, tin, thereby producing a composite having a density about the same as or less than that of aluminum, having high strength, and having good ductility. The ductility is due to the resulting rnicrostructure of the composite. By surrounding the beryllium particles with a ductile envelope phase, a composite is formed where, under load, the beryllium is so constrained by the ductile phase that it and the ductile phase deform continuously.

The 85 percent, by Weight, beryllium composite showed a considerable amount of particle contiguity and would represent, it is thought, an upper limit on the percent by Weight of beryllium contained by the composite. A decrease in beryllium content below 50 percent would raise, it is thought, the density value of the composite to a value of little interest.

Alkali and alkaline earth halogenide agents such as lithium fluoride-lithium chloride or the like in a determined ratio are utilized to segregate to the solid interface of the beryllium particle and either break down the film on the particle of beryllium and/or alter the liquid-solid surface energy in the system.

Therefore, it is an object of the present invention to provide a ductile composite of beryilumcopper-tin in which beryllium is the predominant ingredient.

A further object of the present invention is to provide a ductile beryllium-copper-tin composite having low density and high strength.

Yet another object of the present invention is to provide a ductile composite of beryllium-copper tin containing about 50 to 85 percent, by weight, beryllium, about 13.3 to 50.0 percent, by weight, copper and a trace to 5.5 pecent, by weight, tin.

Another object of the present invention is to provide a ductile beryllium-copper-tin composite having a matrix phase that is heat treatable.

Another object of the present invention is to provide a composite of beryiliumcopper-tin that may be sintered to substantially theoretically density.

Yet another object of the precsnt invention is to pro vide a means and method whereby a ductile berylliumcopper-tin composite may be successfully fabricated in both a practical and economical manner.

Another object of the present invention is to provide a ductllc composite of beryllium-copper-tin containing about 50 to 85 percent, by weight, beryllium and the remainder an alley of copper-tin consisting of a trace to about 11 percent, by weight, tin, the remainder copper.

Yet still another object of the present invention is to provide a means and method of producing a ductile composite of beryllium-coppcr-tin wherein the microstructure consists of beryllium particles surrounded by a ductile envelope phase of a copper-tin-beryllium alloy matrix metal.

Still another object of the present invention is to provide an agent to promote liquid phase sintering of a beryllium copper-tinmixture.

A further object of the present invention is to provide an agent which eliminates the expulsion of an alloy of copper-tiaberyllium from a beryllium specimen.

Still another object of the present invention is to provide alkali and alkaline earth halogenide agents used in the fabrication of a berylliun1copper-tin composite.

A further object of the present invention is to provide a lithium fluoride-lithium chloride agent for promoting liquid phase sintering in a beryllium, copper and tin m-Ix.

Yet still another object of the present invention is to provide a lithium fluoride-lithium chloride agent wherein the constituents are used in a predetermined ratio.

The present invention, in another of its aspects, relates to novel features of the instrumentalities of the invention described herein for teaching the principal object of the invention and to the novel principles employed in the instrumentalities whether or not these features and principles may be used in the said object and/or in the said field.

With the aforementioned objects enumerated, other objects will be apparent to those persons possessing ordinary skill in the art. Other objects will appear in the following description and appended claims. The invention resides in the novel combination of elements and in the means and method of achieving the combination as hereinafter described and more particularly as defined in the appended claims.

In the drawings:

FIGURE 1 is a phase diagram for binary alloys of copper-tin.

FIGURE 2 is a photomicrograph of a beryllium specimen illustrating a copper-tin-berylliurn matrix metal expelled from the specimen by the forces of surface energy of solid beryllium and the copper-tin-beryllium liquid.

FIGURE 3 is an enlargement showing about a 70 percent, by weight, beryllium, about 26.7 percent, by weight, copper, remainder tin composite illustrating beryllium particles surrounded by a ductile envelope phase of a copper-tin-beryllium alloy.

Generally speaking, the means and method of the present invention relate to a ductile beryllium-copper-tin composite fabricated by llquid phase sintering to substantially theoretical density. The composite contains about 50-85 percent, by weight, of beryllium, about 13.3 to 50.0 percent, by weight, coppcr and a trace to about 5.5 percent, by weight, tin.

The method of producing the beryllium-copper-tin composite by liquid phase sintering comprises the steps of mixing predetermined portions of powder beryllium and a powder alloy of copper-tin or copper powder and thin powder with a predetermined portion of an agent selected from the group consisting of alkali and alkaline earth halogenides. The portions are pressed in a die to form a green compact. The compact is then heated to the sintering temperature of beryllium. At this temperature the agent provides a favorable surface energy equilibrium between the beryllium and the copper-tin-alloy so that the alloy progressively dissolves the beryllium at the sintering temperature so as to form a copper-tin-beryllium alloy matrix. Thereafter, the beryllium-coppcr-tin composite may be heat treated and rapidly quenched so as to pre serve the heat treating temperature structure and the copper is supersaturated with tin. Precipitation or ageing may be carried out followed by air cooling to room temperature.

More particularly, the method of the present invention comprises mixing powder beryllium of about 50-85 percent, by weight, with a powder alloy of copper-tin or the elemental powders of copper and tin. An agent of lithium fluoride-lithium chloride in about 0.5 to 2.0 percent, by weight, of the total metal additions is mixed with the beryllium or with the beryllium and the alloy powder or elemental powder. The preferred ratio of the constituents of the agent is about a one to one ratio by weight. The beryllium, the alloy powder or elemental powder, and the agent are pressed so as to form a green compact. The green compact is heated in a non-oxidizing atmosphere such as argon at a temperature of about 1100 C. to about 1200 C. At the aforementioned temperatures, the agent provides a favorable surface energy equilibrium between the beryllium and the alloy so that the copper-tin alloy progressively dissolves the beryllium. The microstructure of the resultant composite consists of beryllium particles surrounded by a ductile envelope phase of a copper-tin-beryllium alloy matrix metal. The alloy is sintered to substantially its theoretical density. The alloy may be specially heat treated and rapidly quenched so that the heat treating temperature structure is preserved and the copper is supersaturated with tin. Precipitation or ageing may he carried out followed by air cooling to room temperature.

In carrying out the present invention, a beryllium base compact is fabricated by any suitable means such as powder metallurgy techniques. A suggested method utilizing this technique is to mix beryllium powder with an agent of equal parts of lithium fluoride-lithium chloride. It is seen that ratio of lithium fluoride to lithium chloride may be varied. The milling is carried out for about 1 hour using ceramic balls. Thereafter, a powder alloy of copper-tin or the elemental powders are ball mill mixed with the beryllium and the agent for an additional hour. The blended and mixed powders are compacted to form a green compact by accepted metallurgical methods such as by compacting within the confines of a die in a hydraulic or an automatic press or by placing the powder in a rubber or plastic mold and compacting in a hydrostatic press. The green compact is sintered in a non-oxidizing atmosphere such as argon or the like at a temperature of about 1100 C. to about 1200 C. It is seen that the range of the sintering temperatures is below the 1277 Centigrade melting point temperature of the beryllium and is above the melting point temperature of the copper-tin alloy. The copper-tin alloy will dissolve smaller beryllium particles and will dissolve the surfaces of the larger beryllium particles with a ductile envelope phase of a copper-tin-beryllium alloy during sintering of the compact. The resultant composite of beryllium-copper-tin had a density of about 98.5 percent of theoretical density.

Composites containing about 50 to 85 percent, by weight, of beryllium, and the remainder an alloy of copper-tin were successfully fabricated. The agent prevented the expulsion of the liquid copper-tin-beryllium alloy from the compact by the forces of surface energy, that is, prevented the formation of very fine rounded droplets of the copper-tin-beryllium alloy on the surface of the beryllium specimen. FIGURE 2 shows a beryllium specimen having on the surface thereof an expelled alloy 21 of copper-tin-beryllium. Specimens from which the copper-tin-beryllium alloy has been expelled have gross porosity and as a result are weak, brittle and of little commercial value.

The composition of the agent utilized is about 50 parts, by weight, of lithium fluoride to about 50 parts, by weight, of lithium chloride. The agent provides an action, such that, upon heating or sintering of the pressed powder mix to the temperature at which the liquid phase forms, expulsion of the melt from the specimen is eliminated. Furthermore, it was found that solution of the beryllium into the alloy was enhanced as evidenced by the rounded droplets of beryllium in the microstructure.

It was found that the amount by weight of lithium fluoride-lithium chloride agent should exceed 0.5 percent, by Weight, of the total of all metal additions. It would appear that the optimum range of the agent is from about 0.5 percent to about 2.0 percent, by weight, of the total of all metal additions. It is believed that the quantity of lithium fluoride-lithium chloride agent required is related to the amount necessary to cover the total beryllium surface area. Hence, the minimum amount of agent needed would be a function of the surface area of the beryllium powder. The utilization of lithium fluoride-lithium chloride agent in other than equal parts was done. It is thought, however, that an equal parts mixture achieves optimum results.

It was found during sintering that substantially 100 percent of the fluxing agent was lost during sintering. This result would seem to indicate that the fluoride and the chloride portion of the fluxing agent volatilized and the lithium portion of the fluxing agent slagged and/or volatilized during the liquid phase sintering operation.

By using the methods of the present invention and the lithium fluoride-lithium chloride agent, compacts were fabricated containing up to 85 percent, by weight, of beryllium, the remainder an alloy of copper-tin without the use of pressure during sintering. Using powder beryllium having a particle size of 20 microns or finer and using ceramic balls to blend the powder metals and the agent resulted in a composite having a high density. The good strength and low density characteristics of the beryllium were retained and the resulting beryllium-coppertin composite was sintered to about 98.5 percent of its theoretical density by a single sinter.

Thus, by substantially surrounding the beryllium particles with a ductile envelope phase of a copper-tinberyllium alloy matrix metal, the beryllium and the matrix metal deform continuously under load.

A copper-tin phase diagram is illustrated in FIGURE 1. Tin strengthens copper by solid solution hardening and precipitation hardening. The theory of the deformation of dispersed particle composite materials states that ductility in such a composite will be enhanced when the constrained fiow stress of the matrix phase can be made as equal as possible to the flow stress of the dispersed particles. Hence, tin is used to harden copper. Once the composite has been cooled to room temperature, the effectiveness of the tin is further brought into play by a subsequent heat treatment. It was found that heat treating the composite at about 350 C. for about 12 hours is sufiicient to completely dissolve all the tin in the copper. The composite is rapidly quenched into a satisfactory medium such as water or the like, such that the high temperature structures are preserved and the copper is supersaturated with tin. Hence, the solutionizing treatment contains all the tin in solution. The tin can be precipitated out of the supersaturated solid solution as an epsilon phase increasing the strength of the copper-tin matrix. An advantage of the 'beryllium-copper-tin composite is that the matrix phase is heat treatable.

Attention is directed to FIGURE 3, wherein a photomicrograph of about 500 magnifications shows a composite of 30 percent, by weight, copper-tin alloy in beryllium after being etched by any suitable etching means such as a dilute solution of ammonium hydroxide and hydrogen peroxide. The areas 10 are beryllium particles. The areas 11 are the copper-tin-beryllium alloy surrounding the beryllium particles.

It will be recognized by those skilled in the art that minor additions of other metals may be added to the matrix of the composite to improve one or more of the physical properties such as machinability, deoxidation, and the like. For example, an addition of a trace to about 1 percent, by weight, of either bismuth manganese or lead to the composite improves machinability thereof. An addition of a trace to about 1 percent, by weight, of magnesium to the composite will improve the deoxidation property of the composite.

Example 1 shows the expulsion of the liquid from a beryllium specimen and Examples 2-9 are illustrative of the preparation of beryllium-copper-tin composites by liquid phase sintering.

EXAMPLE 1 Expulsion of the liquid copper-tin-beryllium alloy from the solid beryllium specimen occurs during liquid phase sintering when the agent of lithium fluoride-lithium chloride is not used in the preparation of a beryllium-coppertin composite.

A mixture of about 70 percent, by weight, of beryllium having a particle size of 200 mesh or finer was ball mill mixed with about 30 percent, by weight, of an alloy of copper-tin or the elemental powder of suitable particle size. The alloy contained about 89 percent, by weight, copper, and about 11 percent, by weight, tin. The milled mixture was pressed by any suitable means such as by an automatic press at a suitable pressure to provide a green compact sturdy enough to be handled. It was found that pressures of from about 15,000 to 20,000 pounds per square inch resulted in a green compact having a density from about 50 to 60 percent of theoretical density and sufficiently strong to be handled. Sintering of the compact was carried out in an argon atmosphere at about 1100 C. for about 1 hour. This technique, due to the surface energies of the solid beryllium and the liquid formed, resulted in the expulsion of the liquid from the specimen and its eventual freezing into rounded globs on the surface of the specimen as shown in FIGURE 2.

EXAMPLE 2 A composite of about 70 percent, by weight, beryllium, bout 26.7 percent, by weight, copper, and the remainder A mixture of about 70 percent, by weight, of beryllium powder having a particle size of 200 mesh or finer was ball mill mixed using ceramic balls with about 30 percent, by weight, of an alloy of copper-tin powder of suitable particle size. The alloy contained about 89 percent, by weight, copper and about 11 percent, by weight, tin. Also ball mi l mixed with the beryllium and alloy powders was about 1.0 percent, by weight, of the total metal additions equal parts of an agent of lithium fluoride-lithium chloride. Mixtures of the beryllium and alloy powders were also prepared with the agent having 0.5 and 2.0 percent, by weight, of the total metal additions using varying ratios of lithium fluoride-lithium chloride. The milled mixture was pressed by any suitable means such as by an automatic press at a suitable pressure to provide a green compact sturdy enough to be handled. It was found that pressures of from about 15,000 to 20,000 pounds per square inch resulted in a green compact having a density of from 50 to 60 percent of theoretical density and sufiiciently strong to be handled. Sintering of the compact was carried out in an argon atmosphere at about 1100 C. for about 1 hour. The density of the composite was about 98.5 percent of theoretical density. The composite was heat treated at about 350 C. for about 1 hour so as to completely dissolve all the tin into the copper. The composite was then rapidly quenched so that the heat treating temperature structure was preserved and the copper was supersaturated with tin. The tin can be precipitated from the supersaturated solid solution as an epsilon phase (see FIGURE 1) thereby precipitation hardening the composite by heating the composite to about 200300 C. for about 6 hours.

EXAMPLE 3 A composite of about 70 percent, by weight, beryllium, about 26.7 percent, by weight, copper, and the remainder tin.

A mixture of beryllium powder having a particle size of 20 microns or finer was ball mill mixed with about 2.0 percent, by weight, of the total metal additions equal parts of an agent of lithium fluoride-lithium chloride. The milling was carried out with ceramic balls for about 1 hour. Thereafter, an alloy powder of about 89 percent, by weight, copper and 11 percent, by weight, tin was ball mill mixed with the beryllium for about 1 hour. Ceramic balls were used to mix the powders. The beryllium constituted about 70 percent, by weight, of the blended powders and the alloy powder constituted about 30 percent of the blended powders. Mixtures of the beryllium and alloy powders were also prepared with the agent having 0.5 and 1.0 percent, by weight, of the total metal additions using varying ratios of lithium chloride to lithium fluoride. The milled mixture was pressed by any suitable means such as by an automatic press at a suitable pressure to provide a green compact sturdy enough to be handled. It was found that pressures of from about 15,000 to 20,000 pounds per square inch resulted in a green compact having a density of from about 50 to 60 percent of theoretical density and sufficiently strong to be handled. Sintering of the compact was carried out in an argon atmosphere at about 1200 C. for about 1 hour, A composite was yielded having a density of about 98.5 percent of theoretical density. Another composite was prepared using the above procedure but sintering for /2 hour. Each composite was heat treated at about 350 C. for about 1 hour so as to dissolve the tin into the copper. Each composite was then rapidly quenched so that the heat treating temperature structure was preserved and the copper was supersaturated with tin. Precipitation of the epsilontin phase is carried out by reheating the composite to about 200-300 C. for about 6 hours followed by air cooling to room temperature.

EXAMPLE 4 A composite of about 70 percent, by weight, beryllium, 26.7 percent, by weight, copper, and the remainder tin.

The procedure of Example 3 was followed using about 70 percent, by weight, beryllium, about 26.7 percent, by weight, copper powder, and the remainder tin powder. Individual composites were prepared using 0.5, 1.0 and 2.0 percent, by weight, of the total metal additions.

EXAMPLE 5 A composite of about 70 percent, by weight, beryllium, 26.7 percent, by weight, copper, and the remainder tin.

The procedure of Example 3 was followed using about 70 percent, by weight, beryllium powder, mixed with about 30 percent, by weight, of an alloy powder of copper-tin. The alloy contains about 89 percent, by weight, copper and about 11 percent, by weight, tin. Individual composites were prepared using 0.5, 1.0 and 2.0 percent by weight of the total metal additions of the agent lithium fluoride-lithium chloride in equal proportions and in unequal proportions at temperatures of about 1100 and 1200 C. for /2 hour and 1 hour using the aforementioned procedure.

EXAMPLE 6 A composite of about 50 percent, by weight, beryllium, about 50 percent, by weight, copper, and a trace of tin.

The procedure of Example 3 was followed using 50 percent, by weight, beryllium powder, mixed with about 50 percent, by weight, of an alloy powder of copper-tin. The alloy contains about 100 percent, by weight, copper and a trace of tin. Individual composites were prepared using 0.5, 1.0 and 2.0 percent by weight of the total metal additions of the agent lithium fluoride'lithium chloride at temperatures of about 1l00 and 1200 C. for /2 hour and for 1 hour using the aforementioned procedure.

EXAMPLE 7 A composite of about 50 percent, by weight, beryllium, about 44.5 percent, by Weight, copper, and the remainder tin.

The procedure of Example 3 was followed using 50 percent, by weight, beryllium powder, mixed with about 44.5 percent, by weight, copper powder and the remainder tin powder. Individual composites were prepared using 0.5, 1.0 and 2.0 percent by weight of the total metal additions of an agent lithium fluoride-lithium chloride at temperatures of about 1100 and 1200 C. for /2 hour and for 1 hour using the aforementioned procedure.

EXAMPLE 8 A composite of about 60 percent, by weight, beryllium, 35.6 percent, by weight, copper, and the remainder tin.

The procedure of Example 3 was followed using 60 percent, by weight, beryllium powder, mixed with about 40 percent, by weight, of an alloy powder of cooper-tin. The alloy contains 89 percent, by weight, copper and 11 percent, by weight, tin. Individual composites were prepared using 0.5, 1.0 and 2.0 percent by weight of the total metal additions of the agent lithium fluoride-lithium chloride at temperatures of about ll00 and 1200 C. for /2 hour and for 1 hour using the aforementioned procedure.

EXAMPLE 9 A composite of about percent, by weight, beryllium, 22.2 percent, by weight, copper, and the remainder tin.

The procedure of Example 3 was followed using percent, by weight, beryllium powder, mixed with about 15 percent, by weight, of an alloy powder of copper-tin. Individual composites were prepared using 0.5, 1.0 and 2.0 percent by weight of the total metal additions of the agent lithium fluoride-lithium chloride at temperatures of about 1100 and 1200" C. for /2 hour and 1 hour using the aforementioned procedure.

The present invention is not intended to be limited to the disclosure herein, and changes and modifications may be made in the disclosure by those skilled in the art without departing from the spirit and scope of the novel concepts of this invention. Such modifications and variations are considered to be within the purview and scope of this invention and the appended claims.

Having thus described our invention, we claim:

1. A ternary metal composite consisting essentially of about 50-85 percent, by weight, of beryllium, and the remainder an alloy of copper-tin.

2. A ternary metal comfosite according to claim 1, Refere ns Cited 3. A metal composite according to claim 1, wherein 202367 2/1937 Donahue 75 150 said composite consisting essentially of about 1 3.3 to 50 5 percent, by Weight, copper, and a trace to about 5.5 per- 3Z3Z3Z88O 6/1967 Kroc}; 25 2 cent, by weight, tin.

4-. A metal composite according to claim 1, wherein REUBEN "FPSTEIN E said alloy of copper-tin consisting essentially of a trace E xamme" to about 11 percent, by Weight, tin, the remainder copper. 10 A. I. TE NER, Assistant Examiner.

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