The primary forms of beryllium produced and used commercially are:
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Metallic beryllium and alloys containing >30% beryllium
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Copper beryllium alloys containing 0.10 – 2.0% beryllium
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Al, Cu and Ni master/casting alloys containing 1 – 15% beryllium
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Beryllium oxide ceramics
PROPERTIES OF BERYLLIUM
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The principal properties of beryllium are its low density, high strength, high rigidity, reflectivity, structural stability at high temperatures and conductivity of heat. Beryllium is notable among metals in terms of specific rigidity; i.e. the ratio of modulus to density.
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The rigidity of beryllium, usually expressed as it modulus, is about 50% greater than that of steel, while its density (1.84
g/cm³) is about 30% less than that of aluminium. The specific rigidity of beryllium is around six times greater than that of
any other metal or alloy, and four times that of composites.
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Beryllium metal is used to produce discrete components used within certain specialised, high technology equipment, where it remains environmentally inert throughout its useful life. Weight is a controlling factor when launching vehicles into space, and lightweight structures are vital. At the same time, however, it is imperative that such structures are rigid, and not subject to distortions or resonant vibrations which might reduce the accuracy of their instrumentation. Beryllium metal is the optimal material for these purposes, principally because of its high specific rigidity. It also has attractive thermal properties which reduce thermal distortions, both at the high temperatures experienced during launch and descent, and also at the sub-zero temperatures of space.
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It is an isotropic material, meaning it has uniform properties in all directions, which increases freedom of design. Its formability, machinability and joinability allow relative ease of manufacture of complex structures. No other material offers this useful combination of properties. The isotropy and thermal properties of beryllium serve to minimise distortions in sophisticated dimensional applications. Beryllium can be machined to form complex curved surfaces, its ability to be highly polished and its ability to accept coatings for enhanced reflectivity at various wavelengths. So too, the structural components made of beryllium offer comparable advantages in combination with the optical components.
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Beryllium remains stable at high temperatures (melting point 1284ºC) and can be used as a heat sink.
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Another special property of the metal is that it is highly transparent to X-rays. In foil form, beryllium is used as the window material for X-ray sources and detectors. It is especially useful in security devices and high-resolution medical imaging technology, such as mammography to detect breast cancer.
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It is the material of choice for the fail-safe final wall lining relied upon to control the high temperature gas plasma of experimental fusion energy reactors. Beryllium is a very efficient moderator of neutrons, slowing and reflecting them, a property that finds application in materials test reactors and in fundamental particle physics research, including efforts to develop clean alternative energy sources, such as the International ITER fusion reactor, now under construction in Europe. It is an extremely useful alloying element, conferring high strength even when added in relatively small proportions to high conductivity alloys, particularly copper-based alloys.
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In solid form, as it is normally supplied and used, the metal is stable and inert. It is neither radioactive, nor water soluble.
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It is corrosion resistant in normal ambient conditions; it is resistant to high temperatures; and it does not give off emissions under the normal range of environmental conditions. It may be handled and stored without special precautions.
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Beryllium metal and composites are used as discrete components within certain specialised, high technology equipment where it remains environmentally inert throughout its useful life
PROPERTIES OF PURE BERYLLIUM
The largest use of beryllium is as an alloying element in copper beryllium alloys that are used to make components, which are inert, stable, and do not give off emissions during use. Beryllium-containing alloys are only used in critical locations in products where they provide a design solution based upon reliability, miniaturisation, improved energy management and /or extending the service life. Almost all high reliability electronic connectors incorporate copper based terminals to carry the current or signal, because of the conductivity provided by this metal. Metals and alloys strengthened by cold working tend to suffer marked strength reduction and weakening after prolonged exposure to elevated temperatures because heat “relaxes” the strengthening stresses that were put into the metal by the cold working. This is obviously a matter of concern for the connectors that must operate in hot environments, such as in automobile engine and transmission control systems, aircraft applications and in many household appliances such as coffee makers, washing machines and dishwashers. Copper beryllium alloys are far less susceptible to these adverse effects and offer the connector designer the highest combinations of strength, conductivity, elevated temperature stress relaxation resistance and formability of any of the copper alloys.
Copper beryllium alloys offer designers the flexibility to employ smaller sized terminals and contacts to obtain the required reliability and performance. Electromechanical relays, switches, or connectors frequently require a design that has a single cantilevered beam section, anchored by insert moulding into a plastic housing. A wide selection of copper alloys is available to designers for use in such applications, and by comparing the mechanical and physical properties of each alloy, the designer will determine the contact size and subsequent price for each candidate alloy. The combination of strength, conductivity and resistance to elevated temperatures provided by copper beryllium alloys allows a designer to use smaller section terminal beams than is possible with other candidate alloys. In addition to reducing the weight of metal required, the use of copper beryllium alloys allows the use of less plastic in the housing which results in using less total energy, and less cost for end-of-life disposal. A significant material weight savings can be achieved by using copper beryllium alloy compared to other common connector alloys. This weight reduction along with superior performance characteristics and reliability are the primary reasons why copper beryllium alloys are frequently selected.
Wrought Copper Beryllium Alloy Compositions
Copper beryllium is manufactured in several distinct compositions. These fall into two categories:
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Alloys selected for high strength (Alloys 25, 190, 290, 25 and 165)
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Alloys selected for high conductivity (Alloys 3, 10, 174 and Brush 60®)
The composition of each is shown in the table below.
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Alloy 25 is the most commonly specified copper beryllium and is available in the wrought forms listed on page 5. In its age hardened condition, Alloy 25 attains the highest strength and hardness of any commercial copper base alloy. The ultimate tensile strength can exceed 200 ksi, while the hardness approaches Rockwell C45. Also, in the fully aged condition, the electrical conductivity is a minimum of 22% IACS (International Annealed Copper Standard). Alloy 25 also exhibits exceptional resistance to stress relaxation at elevated temperatures.
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Alloy 190 is a mill hardened strip product. In other words, the strip is age hardened to a specified strength level as part of the manufacturing process at Brush Wellman prior to shipment. This alloy is similar to Alloy 25 in chemical composition. Alloy 190 is supplied with tensile strength up to 190 ksi and Rockwell hardness to C42. Cost effectiveness is realised by elimination of age hardening and cleaning of stamped parts.
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Alloy 290 is a mill hardened strip product that is similar in strength properties and composition to Alloy 190 but exhibits improved formability. Component reliability and fabrication considerations may require a high strength material with good formability. The improved strength/formability relationship of Brushform® 290 makes it a cost effective alternative to conventional mill hardened product for such applications.
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Alloy 25 / 3325 offers the strength properties of Alloy 25 with the added benefit of being “free machining”. Alloy 25rod and wire contain a small amount of lead to provide an alloy tailored for automatic machining operations. Lead promotes formation of finely divided chips thus extending cutting tool life.
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Alloy 165 contains less beryllium than Alloy 25 and has slightly lower strength. It is less expensive than Alloy 25 and may be substituted when strength is less demanding. Alloy 165 is available in wrought product forms in annealed and aged tempers.
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Alloy 174 and Brush 60® offer users the opportunity to upgrade component performance over bronzes and brasses, particularly where conductivity and stress relaxation resistance are design considerations. Both are supplied with a yield strength up to 125 ksi, superior to other copper alloys such as phosphor bronze, silicon bronze, aluminum brasses, and the copper-nickel-tin alloys. Furthermore, they offer up to fivefold better electrical conductivity than those alloys, and exhibit better stress relaxation resistance. Brush 60® offers an excellent combination of elastic modulus, strength, formability and conductivity. Both are available as mill hardened strip.
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Alloys 3, 7, 10 and 11 combine moderate yield strength, up to 140 ksi, with electrical and thermal conductivity from 45 to 60 percent of pure copper. Alloys 3 and 10 are available in wrought product forms and can be supplied fully hardened. Hardened products are identified by the temper designation AT or HT, and have good formability.
Wrought Copper Beryllium Product Forms
Wrought copper beryllium is available in a variety of product forms. The following paragraphs define the products most commonly specified by copper beryllium users. Strip is flat-rolled product, other than flat wire, 0.188 inch or less in thickness, and supplied in coil form. Wire is a solid section other than strip, furnished in coils or on spools or reels. Wire may be furnished straightened and cut to length, in which case it is classified as rod.
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Flat wire is 0.188 inch or less in thickness and 1-1/4 inch or less in width. This designation includes square wire 0.188 inchor less in thickness. In all cases surfaces are rolled or drawn without having been slit, sheared or sawed. Flat wire is furnished in straight lengths or on spools or reels.
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Rod is a round, hexagonal or octagonal solid section furnished in straight lengths. Rod is supplied in random or specific lengths.
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Bar is a solid rectangular or square section thicker than 3/ 16 inch and up to and including 12 inches wide. Bar is anextruded product. If cut from plate it is called rolled bar. Edges are either sharp, rounded, or have some other simple shape.
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Plate is flat-rolled product thicker than 0.188 inch and over 12 inches wide.
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Tube is a seamless hollow product with round or other cross section. Tube is normally extruded or drawn, and is supplied in random or specific length.
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Extruded shape is a solid section other than round, hexagonal, octagonal, or rectangular. Shapes are produced to the user’s specification and are supplied in straight lengths.
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Forgings, made from cast billet, are supplied in forms ranging from simple geometric configurations to near-net shapes according to user specifications.
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Custom fabricated parts are supplied to customer drawings as finished or semi-finished parts. Such products are fabricated from basic product forms (rod, extrusions, plate, etc.) by processes such as ring rolling, forging, welding and machining.
Copper Beryllium Physical Properties
Copper beryllium’s physical and mechanical properties differ considerably from those of other copper alloys because of the nature and action of the alloying elements, principally beryllium. Varying the beryllium content from about 0.15 to 2.0 weight percent produces a variety of alloys with differing physical properties. Typical values of some of these properties are presented in the table on this page. Whether a high strength or a high conductivity alloy, some physical properties remain similar. For example, the elastic modulus of the high strength alloys is 19 million psi; for the high conductivity alloys, 20 million psi. Poisson’s ratio is 0.3 for all compositions and product forms.
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Thermal Conductivity: A physical property that differs significantly between alloy families is thermal conductivity, whichranges from about 60 Btu/(ft•hr•F) for high strength alloys to 140 Btu/(ft•hr•F) for the high conductivity grades.
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The thermal and electrical conductivities of copper beryllium promote its use in applications requiring heat dissipation and current carrying capacity. Electrical conductivity is listed with mechanical properties in the Product Guide section of this book.
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Thermal Expansion: The thermal expansion coefficient of copper beryllium is independent of alloy content over the temperature range in which these alloys are used. The thermal expansion of copper beryllium closely matches that of steels including the stainless grades. This insures that copper beryllium and steel are compatible in the same assembly. Specific heat of copper beryllium rises with temperature. For Alloys 25, M25 and 165, it is 0.086 Btu/(lb•F) at room temperature, and 0.097 Btu/(lb•F) at 200 F. For Alloys 3, 10, 174 and Brush 60® it rises from 0.080 to 0.091 Btu/(lb•F) over the same temperature range.
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Magnetic permeability: Is very close to unity, meaning that the alloys are nearly perfectly transparent to slowly varying magnetic fields.
Copper beryllium high strength alloys are also less dense than conventional specialty coppers, often providing more pieces per pound of input material, thus in practice a higher unit price of copper beryllium is often compensated by a lower weight required to serve a function, more reliably and consistently.
Copper beryllium also has an elastic modulus 10 to 20 percent higher than other specialty copper alloys.
Strength, resilience, and elastic properties make copper beryllium the alloy of choice for many demanding applications.
