US3438751A

US3438751A - Beryllium-aluminum-silicon composite

Info

Publication number: US3438751A
Application number: US625377A
Authority: US
Inventors: Richard H Krock; Earl I Larsen; Clintford R Jones
Original assignee: PR Mallory and Co Inc
Current assignee: Duracell Inc USA
Priority date: 1967-03-23
Filing date: 1967-03-23
Publication date: 1969-04-15
Anticipated expiration: 1986-04-15

Description

April 15, 1969 R. H. KROCK ET AL 3,438,751

BEBYLLIUM-ALUMINUM-SILICON COMPOSITE Filed March 25, 1967 Sheet of 2 WEIGHT PER CENT SILICON 2 0 3 0 40 50 60 70 80 90 0 IO 50 IOO ATOMIC PER CENT SILICON ALUMINUM-SILICON PHASE DIAGRAM IN VE N TORS RICHARD H. KROCK EARL l. LARSEN CLINTFORD R. JONES ATTORNE Y April 15, 1969 R. H. KROCK ET AL 3,438,751

BERYLLIUM-ALUMINUM-SILICON COMPOSITE Filed March 23, 1967 Sheet 2 of 2 FJZJ1 5 INVENTORS RICHARD H. KROCK EARL LARSEN BY CLlNTFORD R. JONES A TTORNEY United States Patent fice 3,438,751 BERYLLIUM-ALUMINUM-SILICON COMPOSI'I'E Richard H. Krock, Peabody, Mass., Earl I. Larsen,

Indanapolis, 1116., and Clntford R. Jones, Arlington, Mass., assignors to P. R. Mallory & Co. Inc.,

Indianapolis, Ind., a corporation of Delaware Filed Mar. 23, 1967, Ser. No. 625,377

Il1t. Cl. B22f 7/00 U.S. Cl. 29-182.1 4 Clams ABSTRACT OF 'lI-IE DISCLOSURE A two-phase composite material whose microstructure consists of pure beryllium dispersed in an aluminumsilicon-beryllium heat treatable matrix phase was prepared by liquid phase sintering pressed powder mixtures of beryllium, aluminum and silicon.

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, aluminum and silicon 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-atluminum-silicon composites were fabricated in accordance with known liquid phase sintering techniques, it was found that the solid beryllium expelled the liquid aluminum-siliconberyllium alloy from the compact during liquid phase sintering. It is thought that the unfavorable surface energy equilibrium causing expulsion of the liquid aluminum-silicon-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 aluminum-silicon-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 aluminum-silicomberyllium alloy matrix metal thereby avoiding the expulsion of the liquid from the specimen.

Beryllium has several desirable physical features which malte it attractive for a variety of commercial applications such as lightweight gears,"lightweight fasteners, 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 3,438,751 Patented Apr. 15, 1969 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 difficult 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 suflicently 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 above-mentioned 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 outstandng properties of the metal such as, for example, low density combined with high strength. It is thought that U.S. 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 alurninum 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. As stated hereinbefore, 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, aluminum and silicon containing about 50 to percent, by weight, of beryllium, about 13.05 to about 50.0 percent, by weight, aluminum and a trace to about 6.6 percent, by weight, silicon, 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 s due to the resulting microstructure 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 lirnit 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-h'thium 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 beryllium-aluminum-silicon in which beryllium is the predominate ingredient.

Another object of the present invention is to provide an agent to promote liquid phase sintering of a berylliumaluminum-silicon mixture.

Yet another object of the present invention is to provide a composite of beryllium-aluminum-silicon wherein the silicon grains are modified by the addition of small amounts of metallic sodium so as to precipitate out as rounded globules rather than as angular plates thereby producing a more ductile composite.

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

Yet still another object of the present invention is to provide a composite of beryllium-aluminum-silicon wherein the composite may be sintered to substantially theoretical density.

Still another object of the present invention is to provide a ductile beryllium-aluminum-silicon composite baving a. low density and high strength.

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

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

Yet another object of the present invention is to provide a ductile composite of beryllium-aluminum-silicon containing about 50 to 85 percent, by weight, beryllium, about 13.05 to 50.0 percent, by weight, aluminum and a trace to about 6.6 percent, by weight, silicon.

Stil] another object of the present invention is to provide alkali and alkaline earth halogenide agents used in the fabrication of a beryllium-alominum-silicon composite.

Another object of the present invention is to provide a ductile composite of beryllium-aluminum-silicon containing about 50 to 85 percent, by weight, beryllium, and an alloy of aluminum-silicon containing about 87.0 to about 100.0 percent, by weight, aluminum, the remainder silicon.

A further object of the present invention is to provide a lithium fluoride-lithium chloride agent for promoting liquid phase sintering in a beryllium, aluminum and silicon mix.

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.

Yet another object of the present invention is to provide a means and method whereby a ductile berylliumaluminum-silicon composite may be successfully fabricated in both a practical and economical manner.

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 aluminum-silicon.

FIGURE 2 is an enlarged beryllium base specimen illustrating an aluminum-silicon-beryllium matrix metal expelled from the specimen by the forces of surface energy f sglid beryllium and the aluminum-silicon-beryllium 1qui FIGURE 3 is a photomicrograph of about 70 percent, by weight, beryllium, about 26.5 percent, by weight, alumlnum, remainder silicon composite illustrating beryllium particles surrounded by an envelope phase of an aluminum-silicon-beryllium alloy.

FIGURE 4 is a photomicrograph of about 70 percent, by weight, beryllium, about 26.5 percent, by weight, aluminum, remainder silicon composite illustrating a modified alloy matrix surrounding the beryllium particles.

FIGURE 5 is a photomicrograph of about 70 percent, by weight, beryllium, about 26.5 percent, by weight, alummum, remainder silicon composite illustrating a modified alloy matrix surrounding the beryllium particles yvl1erein the alloy matrix has been subjected to solution- 1z1ng and hardening treatments.

Generally speaking, the means and method of the present invention relate to a ductile beryllium-aluminumsilicon composite fabricated by liquid phase sintering to substantially theoretical density. The composite contains about 5085 percent, by weight, of beryllium, about 13.05 to 50.0 percent, by weight, aluminum, and a trace to about 6.6 percent, by weight, silicon.

-The method of producing the berryllium-aluminumsilicon composite by liquid phase sintering comprises the steps of mixing predetermined portions of powder beryll1um and powder alloy of aluminum-silicon or aluminum powder and silicon powder With a predetermined portion of an agent selected from the group consisting of alkali and alkaline earth halogenides. The portions are pressed 111 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 e qurlibrium between the beryllium and the aluminums1licon alloy so that the alloy progressively dissolves the beryllium at the sintering temperature so as to form an aluminum-silicon-beryllium alloy matrix. Thereafter, the beryllium-aluminum-silicon composite may be heat treated to further enhance the physical properties of the matrix pl 1ase of the composite. Small amount sof metallic sod1um may be added to the powder constituents prior to compactxng so as to provide, upon sintering, a modified alloy matrix wherein the silicon tends to precipitate out as rounded globules rather than as angular plates as in the unmodified alloy matrix. The appearance of rounded globules of silicon instead of angular plates of silicon increases the ductility of the alloy matrix of the composite.

More particularly, the method of the present invention comprises mixing powder beryllium of about 50-85 percent, by weight, With a powder alloy of aluminum-silicon or the elemental powders of aluminum and silicon. 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 constituents of the agent are in 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 900 centigrade to about 1150 centigrade. At the aforementioned temperature, the agent provides a favorable surface energy equilibrium between the beryllium and the alloy so that the aluminum-silicon alloy progressively dissolves the beryllium. The microstructure of the resultant composite consists of beryllium particles surrounded by a ductile envelope phase of an aluminum-silicon-beryllium alloy matrix metal. The alloy is sintered to substantially its theoretical density. The allow may be specially heattreated to enhance the physical properties of the matrix phase.

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. The milling is carried out for about 1 hour using ceramic balls. Thereafter, a powder alloy of aluminum-silicon or the elemental powders are ball mill mixed with the beryllium and the agent for an additional hour. T he 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 powders in a rubber or a 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 900 centigrade to about 115 0 centigrade. 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 577 centigrade melting point temperature Of the aluminum-silicon alloy. The aluminum-silicon a1- loy Will dissolve smaller beryllium particles and Will dissolve the surfaces of the larger beryllium powder particles so as to surround the remaning beryllium particles with a ductle envelope phase of aluminum-silicon-beryllium alloy during sintering of the compact. The resultant composite of berylliurn-aluminum-silicon had a density of about 99.2 percent of theoretical density.

Composites containing about 50 to 85 percent, by weight, of beryllium, and the remainder an alloy of aluminum-silicon were successfully fabricated. The agent prevented the expulsion of the liqud aluminum-silicon-beryllium alloy from the compact by the forces of surface energy, that is, prevented the formafion of vefy fine rounded droplets of the aluminum-silicon-beryllium alloy on the surface of the beryllium specimen. FIGURE 2 shows a beryllium speciment 20 having on the surface thereof an expelled alloy 21 of aluminum-silicon-beryllium. Specimens from which the aluminum-silicon-beryllium alloy has been expelled have gross porosity and as a result are weak, brittle, and of little commercal 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 liqud 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 particles by beryllium in the micro-structure.

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 frorri 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 fnnction of the surface area of the beryllium powder. The utilization of lithium fluoride-lithium chloride agent in other than equal parts is possible. 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. This resultant would seem to indicate that the fluoride and chloride portion of the fluxing agent volatilzed and the lithium portion of the fluxing agent slagged and/or volatilized during the liqud phase sintering operation.

By using the methods of the present invention and the lithium fluoride-lithium chloride agent, compacts were fabricated containing up to percent, by weight, of beryllium, the remainder an alloy of aluminum-silicon without the use of pressure during sintering. The composite was sintered to about 93.5 percent of its theoretical density by a single sinter and achieved about 98 percent of theoretical density by a repress and an intermediate reliquid phase sinter for about 1 hour. 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 density of about 99.92 percent of theoretical density by a single sinter. The good strength and low density characteristics of the beryllium were ret-ained and the resulting beryllium-aluminum-silicon composite possessed good ductility.

Thus, by substantially surrounding the beryllium partcles with a ductle envelope phase of an aluminum-siliconberyllium alloy matrix metal, the beryllium and the matrix metal deform continuously under load.

An aluminum-silicon phase diagram is illustrated in FIGURE 1.

Silicon is an effective material for strengthenng aluminum. A11 the aluminum silicon alloys show some ductility since alpha aluminum is the continuous phase in the eutectic composition. However, since in normal alloys the eutectiferous silicon crystallites tend to be angular plates whose sharp edges act as internal notches in the structure thereby serving as nucleation sites for fracture so as to reduce the ductility of the alloy. FIGURE 3 shows the angular plates of silicon 12 formed in the matrix 11 surrounding the beryllium particles 10. Modification of the alloy system can be achieved by small additions of metallic sodium which substantially suppresses the nucleation of the silicon crystals, lowers the eutectic temperature from 577 C. to 550-560 C. and increases the silicon in the eutectic composition from about 11.7 percent, by weight, to about 12- 13 percent, by weight. FIGURE 4 illustrates the rounded globules of silicon 12 forrned in the matrx 11 surrounding the beryllium particles 10.

As seen above, two important eir'ects are noted as a result of the addition of metallic sodium into aluminumsilicon melts, that is the proeutectic and eutectic silicon tends to precipitate out in the form of rounded globules rather than as angular plates and the eutectic point shifts from about 11.7 percent, by weight, silicon to about 13 percent, by weight, silicon.

The phase diagram of aluminum-silicon shown in FIG- URE 1 illustrates that the eutectic composition of the normal alloy is about 11.7 percent, by weight, silicon meaning that alloys of less than 11.7 percent silicon Will precipitate out proeutectic aluminum and alloys with greater than 11.7 percent silicon Will precipitate out proeutectic silicon. The sodium modification treatment shifts the eutectic point to about 13 percent, by weight, silicon, thus in the modified alloy, a 12 percent, by weight, silicon alloy will precipitate out proeutectic aluminum rather than proeutectic silicon as the phase diagram of the normal alloy would indicate.

Assuming a compact of about 50-85 percent, by weight, beryllium, the remainder an aluminum-silicon alloy with silicon less than 1.65 percent, by weight, to aluminum, with no addition of metallic sodium, heating of the compact is carried out at about 900-1150" C. followed by cooling to room temperature. The composite consists of beryllium particles dispersed in an aluminum-silicon alloy matrix. Heating the composite to about 570 C. will dissolve all the silicon into the aluminum. Quenching the composite from the elevated temperature preservcs structure obtained at the elevated temperature, hence, the aluminum matrix is supersaturated with respect to silicon srnce aluminum can dissolve about 1.65 percent, by weight, s1licon -at 570 C. and can dissolve virtually no silicon at room temperature. The supersaturated matrix can be precrprtation hardened by a tempering treatment at 300-400 C. for about 1-2 hours which will precipitate the silicon 7 that is supersaturated in the aluminum lattice as a second phase in the aluminum matrix. FIGURE illustrates the composite after it has been precipitation hardened. Beryllium particles 10 are surrounded by a matrix 11 including precipitated silicon particles 12.

In the situation of a composite having 50-85 percent, by weight, beryllium, the remainder an unmodified alloy of aluminum-silicon with silicon less than 11.7 percent, by weight, the alloy is hypoeutectic and upon cooling from the sintering temperature, proeutectic aluminum crystals are precipitated. Since the alloy is unmodified, the eutectic silicon appears as angular plates whose sharp edges act as internal notches in the structure thereby reducing the ductility of the structure. When the composites are subjected to solutionizing the hardening treatments, as described above, the aluminum rich part of the eutectic reacts as described hereinabove. In addition, the solutionizing treatment slightly coarsens and rounds the eutectic silicon.

In composites wherein the aluminum-silicon matrix is modified by the addition of about 0.25 percent, by weight, metallc sodium, the eutectic is driven to about 13 percent, by weight, silicon. Thus, in composites wherein the percent by weight of silicon is greater than 1.65 percent and less than 13 percent, ali proeutectic precipitate on cooling from the sintering temperature is still aluminum crystals, and as discussed above, the eutectic silicon grains are now rounded rather than angular plates. Solutionizing and tempering has the effect of hardening the aluminum rich part of the eutectic composition as discussed above and in addition, coarsens the size of the rounded eutectic silicon rich crystals.

Comp0sites having a silicon content in excess of 11.7 percent, by weight, relative to aluminum in the normal or unmodified alloy and silicon contents in excess of 13 percent, by weight, in modified alloys, the proeutectic phase is silicon rich crystals. The modified alloys would consist of beryllium particles in an aluminum-silicon eutectic matrix with some proeutectic silicon crystals present. In modified alloys, the shape of both the proeutectic and eutectic silicon crystals would be rounded, in unmodified alloys, the shape of the proeutectic and eutectic crystals of silicon would be angular plates. Otherwise, treatments and microstructure changes are as described above.

As with the fluxing agent, the sodium addition tends to slag and/or volatilize from the composite during liquid phase sintering.

Example 1 shows the expulsion of the liquid from a beryllium specimen and Examples 2-14 are illustrative of the preparation of beryllium-aluminum-silicon composites by liquid phase sintering.

Example 1 Expulsion of the liquid aluminum-silicon-beryllium alloy from the solid beryllium specimen during liquid phase sintering When the agent of lithium fluoride-lithium chloride is not used in the preparation of a beryllium-aluminum-silicon composite, and wherein the alloy matrix is unm0dified.

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 unmodified alloy of aluminum-silicon or the elemenal powder of suitable particle size. The alloy contained about 88.3 percent, by weight, aluminum and about 11.7 percent, by weight, silicon. 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 sufiicicntly strong to be handled. Sintering of the compact was carried out in an argon atmosphere at about 1100 centigrade 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, about 26.5 percent, by weight, aluminum, and the remainder silicon, the composite having an unmodified alloy matrix.

A mixture of about 70 percent, by weight, beryllium powder having a particle size of 200 mesh or finer was ball mill mxed with about 30 percent, by weight, of an alloy of aluminum-silicon powder of suitable particle size. The alloy contained about 88.3 percent, by weight, aluminum and about 11.7 percent, by weight, silicon. Also ball mill 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 fluor delithium 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. 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 baving a density of from 50 to 60 percent of theoretical density and sufiiciently strong to be handled. The compact was sintered and repressed. Resintering of the compact was carried out in an argon atmosphere at about 1100 centigrade for about 1 hour raised the density of the composite from about 93.5 percent to about 98 percent of theoretical density. The composite is heat-treated at about 570 centigrade for about 1 hour SO as to completely dissolve all the silic0n into the aluminnm. The composite is then rapidly quenched so that the structure at the heat-treating temperature is preserved and the aluminum is super-saturated with silicon. The supersaturated matrix can be precipitation hardened by an ageing treatment at 300-400 C. for 1-2 hours which will precipitate the silic0n that was supersaturated in the aluminum lattice as a second phase in the matrix.

Example 3 A composite of about 70 percent, by weight, beryllium, 26.5 percent, by weight, aluminum, and the remainder silicon, the composite having a modified alloy matrxx.

A mixture of beryllium powder having a particle size of 20 micron or finer was ball mill mixed with about 2.0 percent, by weight, of the total metal additions egual parts of an agent of lithium fluoride-lithium chloridc. The milling was carried out with ceramic balls for abou: 1 hour. Thereafter, an alloy powder of 88.3 percent, by weight, aluminum, 11.7 percent, by weight, silicon., and .25 percent by Weight of the alloy additions of metallic sodium were ball mill mixed with the beryllium and the agent 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. Mix. tures 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. 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 15,000 to 20,000 pounds per square inch resulted in a green compact having a density cf from about 50 to 60 percent of theoretical density and sufliciently strong to be handled. The compact was sintered and repressed. Resintering of the compact was carried out in an argon atmosphere at about 1150 centigrade for about 1 hour. Another composite was prepared using the above procedure but sintered for about '/2 hour. It was found that the composite sintered for 1 hour had a density of about 99.92 percent of theoretical density and the composite sintered for about /2 hour had a. density of about 99.85 percent of theoretical density. Bach composite was heat-treated at about 570 ccntigrade for about 1 hour so as to dissolve the silicon into the aluminum. Several of the modified composites were precipitation hardened by an ageing treatment at about 400 centigrade for about 1 hour so that the silicon that was supersaturated in the aluminum lattice precipitates as a second phase in the matrix. Other composites were precipitation hardened using a time-temperature treatment of 2 hours at 300 C.

Example 4 A composite of about 70 percent, by Weiglzt, beryllium, about 26.5 percent, by weight, aluminurn, and the remainder silicon, the composite having a modified alloy matrix.

The procedure of Example 3 was followed using about 70 percent, by weight, beryllium about 26.5 percent, by weight, aluminum powder, and the remainder silicon powder. 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 1000 centigrade for /2 hour and 1 hour using the aforementioned procedure.

Example 5 A composite of about 70 percent, by weight, beryllium, about 26.5 percent, by weight, aluminum, and the remainder silicon, the composite having a modified alloy matrix.

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 aluminum-silicon. The alloy contains 88.3 percent, by weight. aluminum and 11.7 percent, by Weight, silicon. 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 900 centigrade for /2 hour and 1 hour using the aforementioned procedure.

Example 6 A composite of about 50 percent, by weight, beryllium, about 49.18 percent, by weight, aluminum, and the remainder silicon, the composite having a modified alloy matrix.

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 aluminumsilicon. The alloy contained about 98.35 percent, by weight, aluminum and about 1.65 percent, by Weight, silicon. Individual composites were prepared using 0.5, 1.0 and 2.0 percent by weigbt of the total metal additions of the agent lithium fiuoride-lithium chloride at tem: peratures of about 900, 1000, 1100 and 1150 centigrade for /2h0111 and for 1 hour using the aforementioned procedure.

Example 7 A composite of about 50 percent, by weight, beryllium, about 43.5 percent, by weight, aluminum, and the remainder silicon, the composite having a modified alloy matrix.

The procedure ofExample 3 was followed using 50 percent, by weight, beryllium powder, mixed With about 50 percent, by weight, of an alloy powder of aluminumsilicon. The alloy contained about 87.0 percent, by weight, aluminum and about 13.0 percent, by weight, silicon. 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-litbium chloride at temperatures of about 900, 1000, 1100" and 1150 centigrade using the aforementioned procedure.

10 Example 8 A composite of about 60 percent, by weight, beryllium, about 39.34 percent, by weight, aluminum, and the remainder silicon, the composite having a modified alloy matrix.

The procedure of Example 3 was followed using about 60 percent, by weight, beryllium powder, mixed With about 40 percent, by weight, of an alloy powder of aluminum-silic'on. The alloy contained about 98.35 percent, by Weight, aluminum and about 1.65 percent, by weight, silicon. 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 900, 1000, 1100 and 1150 centigrade for /2 hour and for 1 hour using the aforementioned procedure.

Example 9 A composite of about 60 percent, by Weight, beryllium, about 34.8 percent, by weight, aluminum, and the remainder silicon, the composite having a modified alloy matrix.

The procedure of Example 3 was followed using about 60 percent, by weight, beryllium powder, mixed With about 40 percent, by weigbt, of an alloy powder of aluminum-silicon. The alloy contained about 87 percent, by Weight, aluminum and about 13 percent, by weight, silicon. 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 900, 1000, 1100 and 1150 centigrade using the aforementioned procedure.

Example 10 A composite of about 75 percent, by weight, beryllium, about 21.75 percent, by weight, aluminum, and the remainder silicon, the composite having a modified alloy matrix.

The procedure of Example 3 was followed using 75 percent, by weight, beryllium powder, mixed With about 25 percent, by weight, of an alloy powder of aluminumsilicon. The alloy contained about 87 percent, by Weight, aluminum and about 13 percent by weight, silicon. 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 900, 1000", 1100 and 1150 centigrade for V2 hour and for 1 hour using the aforementioned procedure.

Example 11 A composite of about 75 percent, by weight, beryllium, about 24.59 percent, by Weight, aluminum, and the remainder silicon, the composite having a modified alloy matrix.

The procedure of Example 3 was followed using about 75 percent, by weight, beryllium powder, mixed With about 25 percent, by weight, of an alloy powder of aluminum-silicon. The alloy contained about 98.35 percent, by weight, aluminum and about 1.65 percent, by weight, silicon. 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 900, 1000, 1100 and 1150 centigrade using the aforementioned procedure.

Example 12 A composite of about percent, by weight, beryllium, about 13.05 percent, by weight, aluminum, and the remainder silicon, the alloy having a modified alloy matrix.

The procedure of Example 3 was followed using about 85 percent, by weight, beryllium powder, mixed with about 15 percent, by weight, of an alloy powder of aluminum-silicon. The alloy contained about 87 percent, by Weight, aluminum and about 13 percent, by weight, silicon. Individual composites were prepared using 0.5, 1.0

11 and 2.0 percent, by weight of the total metal additions of the agent lithium fluoride-lithiurn chloride at temperatures of about 900, 1000, 1100 and 1150 centigrade for /2 hour and 1 hour using the aforementioned procedure.

Example 13 A composite of about 85 percent, by weight, beryllium, about 14.75 percent, by weight, aluminum, and the remainder silicon, the alloy having a modified alloy matrix.

The procedure of Example 2 was followed using about 85 percent, by weight, beryllium powder, mixed with about 15 percent, by weight, of an alloy powder of aluminum-silicon. The alloy contained about 98.35 percent, by weight, aluminum and about 1.65 percent, by weight, silicon. 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 900, 1000, 1100 and 1150 centigrade using the aforementoned procedure.

Example 14 A composite of about 50 percent, by weight, beryllium, about 44.15 percent, by weight, aluminum, and the remainder silicon.

The procedure of Example 2 was followed using 50 percent, by weight, beryllium powder, mixed with about 50 percent, by weight, of an alloy powder of aluminumslicon. The alloy contained about 88.3 percent, by weight, aluminum and about 11.7 percent, by weight, silicon. Individual composites were prepared using 0.5, 1.0 and 2.0 percent, by weight, of the total metal additions of the agent lthium fluoride-lithium chloride at temperatures of about 900, 1000, 1100 and 1150 centigrade for /2 hour and for 1 hour using the aforementioned procedure.

Example 15 A composite of about 85 percent, by weight, beryllium, about 13.25 percent, by weight, aluminum, and the remainder silicon.

The procedure of Example 2 was followed using about 85 percent, by wei-ght, beryllium powder, mixed with about 15 percent, by weight, of an alloy powder of aluminum-silicon. The alloy contained about 88.3 percent, by Weight, aluminum and about 11.7 percent, by weight, silicon. 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-lithiurn chloride at temperatures of about 900, 1000, 1100 and 1150 centigrade for /2 hour and for 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 modificatons 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 -85 percent, by weight, of beryllium, and the remainder an alloy of aluminum-silicon.

2. A ternary metal composite according to claim 1, Wherein said beryllium particles are surrounded by a matrix of an alloy of aluminum-silicon-beryllium.

3. A metal composite according to claim 1, wherein said alloy contains about 13.05 to 50.0 percent, by Weight, aluminum and a trace to about 6.6 percent, by weight, silicon.

4. A ternary metal composite according to claim 1, wherein said matrix alloy contains about 87 to about 100.0 percent, by weight, aluminum and the remainder silicon.

References Cited UNIT ED STATES PATENTS 2/1937 Donahue -150 4/1968 Larsen 29-182.1

U.S. Cl. X.R. 29-182; 75-150