US3490959A - Beryllium composite - Google Patents

Beryllium composite Download PDF

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US3490959A
US3490959A US526746A US3490959DA US3490959A US 3490959 A US3490959 A US 3490959A US 526746 A US526746 A US 526746A US 3490959D A US3490959D A US 3490959DA US 3490959 A US3490959 A US 3490959A
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beryllium
silver
percent
weight
composite
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Richard H Krock
Clintford R Jones
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Duracell Inc USA
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PR Mallory and Co Inc
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/0408—Light metal alloys

Definitions

  • the present invention relates to prime composites of beryllium and more particularly to means and methods for providing such composites through liquid phase sintering.
  • Liquid phase sintering differs from the several other 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 to a temperature wherein a predetermined amount of the liquid phase appears.
  • the liquid phase one of the metal constituents, the solid, is progressively dissolved in the other metal constituent, the liquid.
  • 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.
  • the present invention prevents the expulsion of the liquid 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 fiuxing 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 a silver-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 applications such as lightweight gears, lightweight fasteners, airplane parts or the like.
  • Some of the more desirable features of beryllium metal are a density of 1.82 grams per cubic centimeter as compared to 2.7 grams per cubic centimeter for aluminum, a high elastic modulus of 40 10 pounds per square inch as compared to 30x10 pounds per square inch for steel, a high melting temperature of 1285 centigrade, extremely high specific stiffness, good strength, excellent dimensional stability, low capacity for neutron absorption, most elfective metal for slowing and reflecting neutrons, and good corrosion resistance in air and water. It is seen that beryllium metal is lighter than aluminum metal and has a melting temperature that is about twice that of aluminum.
  • beryllium is very transparent to X-rays. This factor, in conjunction with its high melting point, makes beryllium suitable for use as windows in X-ray tubes.
  • beryllium has one major drawback which has seriously limited its commercial acceptance, that is, beryllium is inherently brittle at room temperature.
  • beryllium alloys might be fabricated by pressing and sintering a mix of metal powders.
  • 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 liquid 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 and a metal such as silver containing up to percent, by weight, of beryllium thereby producing a composite having a density less than that of aluminum, having high strength, and having good ductility.
  • the ductility is due to the resulting microstructure of the composite.
  • 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 liquidsolid surface energy in the system.
  • a further object of the present invention is to provide a ductile beryllium composite having a low density and high strength.
  • a further object of the present invention is to provide a ductile composite of beryllium in which beryllium is the predominate ingredient.
  • Another object of the present invention is to provide a means and method of producing a ductile composite of beryllium-silver whose microstructure consists of beryllium particles surrounded by a ductile envelope phase of a silver-beryllium alloy matrix metal.
  • Yet another object of the present invention is to provide a ductile composite of beryllium containing 60 percent, by weight, or more of beryllium.
  • Yet still another object of the present invention is to provide a ductile composite of beryllium-silver containing about 75 percent, by weight, beryllium, and the remainder silver.
  • a further object of the present invention is to pro-vide an agent which eliminates the expulsion of a matrix metal 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 beryllium composite.
  • Another object of the present invention is to provide a composite of beryllium-silver that may be sintered to substantially theoretical density.
  • Yet another object of the present invention is to provide a means and method whereby a ductile beryllium composite may be successivefully fabricated in both a practical and economical manner.
  • a further object of the present invention is to provide a lithium fluoride-lithium chloride agent for promoting liquid phase sintering in a beryllium and silver 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.
  • 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.
  • FIGURE 3 is a photomicrograph of a 25 percent, by weight, silver in beryllium composite illustrating a delta or a gamma intermediate phase surrounding the beryllium particles.
  • FIGURE 4 is a photomicrograph of a 25 percent, by weight, silver in beryllium composite illustrating the absence of the delta or the gamma intermediate phase.
  • the means and method of the present invention relate to a ductile beryllium composite fabricated by liquid phase sintering.
  • the composite contains from about 60 to percent, by Weight, of beryllium, and the remainder silver.
  • the method of producing the beryllium-silver composite by liquid phase sintering comprises the steps of mixing predetermined portions of powder beryllium and powder silver together with a predetermined portion of an agent selected from the group consisting of alkall and akaline earth halogenides.
  • the portions are pressed in a die to form a green compact.
  • the compact is then heated to the sintering temperature.
  • the agent provides a favorable surface energy equilibrium between the beryllium and the silver so that the silver progressively dissolves the beryllium at the sintering temperature.
  • the composite is quenched or heat treated so as to substantially eliminate the formation of a gamma or of a delta phase in the alloy.
  • the agent provides a favorable surface energy equilibrium between the beryllium and the silver so that the silver progressively dissolves the beryllium.
  • the microstructure of the resultant composite consists of beryllium particles surrounded by a ductile envelope phase of a silver-beryllium alloy matrix metal.
  • the alloy is sintered to substantially its theoretical density.
  • the alloy is then quenched or specially heat treated so as to substantially avoid the formation of a gamma phase or a delta phase in the alloy.
  • 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 powdered silver and an agent of equal parts of lithium fluoridelithium chloride.
  • the powders are blended and mixed by ball milling the metal powders and the flux agent.
  • 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 powders in a rubber or a plastic mold and compacting in a hydrostatic press.
  • the green compact is sintered in a non-oxidzing atmosphere such as argon or the like at a temperature of about 1050 centigrade to about 1250 centigrade. It is seen that the range of the sintering temperatures is below the l277 centigrade melting point temperature of beryllium but above the 960.8 centigrade melting point temperature of silver.
  • the silver will dissolve smaller beryllium particles and will dissolve the surfaces of the larger beryllium powder particles thereby surrounding the remaining beryllium particles with a ductile envelope phase of a silver-beryllium alloy.
  • the agent lithium fluoride-lithium chloride, either breaks down the oxide film on the beryllium or segregates to the metal oxide interface lowering the Surface energy of the liquid metal with respect to the beryllium oxide film. Simply, the agent causes the liquid to wet the beryllium.
  • FIGURE 2 shows a beryllium specimen 20 having on the surface thereof an expelled alloy 21 of silver-beryllium. Specimens from which the silver-beryllium alloy has been expelled have gross porosity and as a result are weak, brittle, and of little commercial value.
  • composition of the agent utilized is about 50* parts, by weight, of lithium fluoride to about 50 parts, by Weight, of lithuim 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 silver was enhanced as evidenced by the rounded particles or beryllium in the microstructure.
  • 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 is possible. It is thought, however, that an equal parts mixture achieves optimum results.
  • the beryllium-silver phase diagram of FIGURE 1 illustrates that'beryllium-silver mixtures having a beryllium content in excess of about 2.3 percent, by weight, form a melt and are in equilibrium with substantially pure beryllium at temperatures above about l0 centigrade.
  • the composition of the silver-beryllium alloy melt is deterr'nined by the temperature of the melt and is independent of the percent, by weight, of beryllium while the relative amount of the solid beryllium and of the matrix metal at the sintering temperature is determined by the temperature itself, as well as by the percent, by weight, of beryllium relative to the percent, by weight, of silver.
  • Beryllium-silver mixtures have been sintered at a plurality of temperatures between 1050 centigrade and 1250 centigrade. Liquid phase structures have been obtained at each of the temperatures at which the compact was sintered. It was noted that when the percent, by volume, of the liquid is less than about 5 percent, the sintering in the liquid phase is slow and porosity is apparent in the materials. It was also noted that when the percent of volume of the liquid exceeds about 35 percent, the solid beryllium particles are not capable of maintaining the structure intact and as a result thereof, sagging of the pressed compact may be observed. Hence, for a particular alloy, temperature ranges for sintering can be predicted from the phase diagram, and these temperature ranges have been corroborated by experimentation.
  • the density values of the composite are between the density of beryllium and the density of aluminum.
  • Composites containing from about 60 to about 75 percent, by weight, of beryllium may be sintered from about 96 to about 99 percent of density by a single sinter.
  • Composites containing about 85 percent, by weight, of beryllium require a double pressing and sintering operation to attain about 95 percent of theoretical density.
  • the beryllium particles react with the silver rich liquid through a peritectic reaction whereby a new phase, delta, is formed below a temperature of about 1010 centigrade.
  • the delta phase which is in equilibrium with the solid beryllium between about 10l0 centigrade and 850 centigrade contains about 18 percent, by weight, of beryllium.
  • Additional cooling to a temperature between abut 850 and about 760 centigrade results in reaction of the delta phase with solid beryllium particles to form a gamma phase in equilibrium with the beryllium particles.
  • the gamma phase contains about 12 percent, by weight, of beryllium.
  • the gamma phase reacts with the beryllium particles so as to form substantially solid silver in equilibrium with substantially pure beryllium.
  • FIGURE 3 wherein a photomicrograph of 500 magnifications shows a composite of 25 percent, by weight, silver'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 dark areas 11 are the intermediate delta or gamma phase surrounding the beryllium particles.
  • FIGURE 4 shows the appearance of the composite of 25 percent, by weight, silver in beryllium after heat treating at 750 Centigrade in an argon atmosphere for about 24 hours. Note that the delta or the gamma phase has been removed.
  • the areas 10 are the sintered beryllium particles and the area 12 is the ductile silverberyllium alloy matrix which surrounds the sintered beryllium particles.
  • Example 1 shows the expulsion of the liquid from a beryllium specimen and Examples 2 to 4 are illustrative of the preparation of beryllium-silver composites by liquid phase sintering.
  • EXAMPLE 1 Expulsion of the liquid silver-beryllium alloy from the solid beryllium specimen when the agent of lithium fluoride-lithium chloride is not used in the preparation of a beryllium-silver composite.
  • a mixture of about 75 percent, by weight, of beryllium having a particle size of 200 mesh or finer was ball mill mixed with about 25 percent, by weight, of silver powder of suitable particle size.
  • 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 sufiiciently strong to be handled. Sintering of the compact was carried out in an argon atmosphere at about 1150 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.
  • EXAMPLE 2 A composite of about 60 percent, by weight, beryllium and about 40 percent, by weight, of silver.
  • a mixture of about 60 percent, by weight, of beryllium having a particle size of 200 mesh or finer was ball mill mixed with about 40 percent, by weight, of silver powder of suitable particle size. Also ball mill mixed with the beryllium powder and the silver powder was about 1.0 percent, by weight, of the total metal additions equal parts of an agent of lithium fluoride-lithium chloride. Mixtures of beryllium and silver 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.
  • EXAMPLE 3 A composite of about percent, by weight, beryllium and about 25 percent, by weight, silver.
  • Example 2 The procedure of Example 2 was followed using 75 percent, by weight, of beryllium and 25 percent, by weight, of silver. An individual composite was prepared at each of the following temperatures of about l050, 1100", ll5 (;l, 1200", 1225 and 1250" centigrade using the aforementioned procedure.
  • EXAMPLE 4 A composite of about percent, by weight, beryllium and about 15 percent, by weight, silver.
  • Example 2 The procedure of Example 2 was followed using about 85 percent, by weight, of beryllium and about 15 percent, by weight, of silver. An individual composite was prepared and heated to one of the following temperatures of about l050, 1100", 1150, 1200, 1225 and 1250 centigrade.
  • a mixture consisting essentially of about 60 to about 85 weight percent beryllium and up to 2 weight percent of a lithium halogenide, the remainder being essentially silver.

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US526746A 1966-02-11 1966-02-11 Beryllium composite Expired - Lifetime US3490959A (en)

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AT (1) AT285191B (xx)
BE (1) BE693954A (xx)
CH (1) CH501732A (xx)
DE (1) DE1558529A1 (xx)
FR (1) FR1572139A (xx)
GB (1) GB1129504A (xx)
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3768983A (en) * 1971-11-03 1973-10-30 North American Rockwell Single crystal beryllium oxide growth from calcium oxide-beryllium oxide melts
US5421916A (en) * 1993-09-03 1995-06-06 Nuclear Metals, Inc. Light weight, high strength beryllium-aluminum alloy

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2244608A (en) * 1939-02-09 1941-06-03 Cooper Wilford Beryllium Ltd Process of making alloys of aluminum beryllium
US2287251A (en) * 1939-07-07 1942-06-23 Jones William David Manufacture of nonporous metal articles
US3264147A (en) * 1963-10-16 1966-08-02 Honeywell Inc Beryllium alloy and process

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2244608A (en) * 1939-02-09 1941-06-03 Cooper Wilford Beryllium Ltd Process of making alloys of aluminum beryllium
US2287251A (en) * 1939-07-07 1942-06-23 Jones William David Manufacture of nonporous metal articles
US3264147A (en) * 1963-10-16 1966-08-02 Honeywell Inc Beryllium alloy and process

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3768983A (en) * 1971-11-03 1973-10-30 North American Rockwell Single crystal beryllium oxide growth from calcium oxide-beryllium oxide melts
US5421916A (en) * 1993-09-03 1995-06-06 Nuclear Metals, Inc. Light weight, high strength beryllium-aluminum alloy

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GB1129504A (en) 1968-10-09
AT285191B (de) 1970-10-12
CH501732A (de) 1971-01-15
FR1572139A (xx) 1969-06-27
DE1558529A1 (de) 1970-04-16
BE693954A (xx) 1967-08-10
NL6702040A (xx) 1967-08-14

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