Beryllium and Beryllium Alloys

Abstract

AbstractBeryllium, Be, is the only light metal having a high melting point. The majority of the beryllium commercially produced is used in alloys, principally copper–beryllium alloys. The usage of unalloyed beryllium is based on its nuclear and thermal properties, and its uniquely high specific stiffness, ie, elastic modulus/density values. Beryllium oxide ceramics are important because of the very high thermal conductivity of the oxide, serving also as an electrical insulator. The beryllium content of the earth's surface rocks has been estimated at 4–6 ppm. Of beryllium‐containing minerals, only beryl and bertrandite are of commercial significance. One of the more important characteristics of beryllium is its pronounced anisotropy resulting from the close‐packed hexagonal crystal structure. This factor must be considered for any property that is structure sensitive. At ambient temperatures beryllium is quite resistant to oxidation; highly polished surfaces retain their brilliance for years. Beryllium is susceptible to corrosion under aqueous conditions, especially when exposed to solutions containing the chloride ion. It is rapidly attacked by seawater. Protective systems used for beryllium include chromic acid passivation, electroless plating, and paints. Beryllium reacts readily with sulfuric, hydrochloric, and hydrofluoric acids. Chemically, beryllium is closely related to aluminum, from which complete separation is difficult. The Kjellgren‐Sawyer sulfate process is used commercially for the extraction of beryl. The Schwenzfeier process is used to prepare a purified, anhydrous beryllium fluoride, BeF2, for reduction to the metal. For both ecological and economic reasons there is no electrolytically derived beryllium available in the marketplace. Because beryllium is primarily used as a powder metallurgy product or as an alloying agent, casting technology is not commonly utilized. Most beryllium hardware is produced by powder metallurgy techniques providing a strong material with substantial ductility at room temperature. Beryllium powder is manufactured from vacuum‐cast ingot using impact grinding or jet milling. Hot‐isostatic‐pressing (HIP) is replacing the vacuum hot‐pressing procedure for all but the largest shapes. Beryllium, beryllium‐containing alloys, and beryllium oxide ceramic in solid or massive form present no hazard whatsoever. Solid shapes may be safely handled with bare hands; however, inhalation of fine airborne beryllium may cause chronic beryllium disease, a serious lung disease in certain sensitive individuals. The U.S. Occupational Safety and Health Administration (OSHA) has adopted workplace exposure limits designed to keep airborne concentrations well below the levels known to cause health problems. Beryllium is typically recycled; thus, it is not a waste disposal problem. Beryllium is used extensively as a radiation window, both in source and detector applications, because of its ability to transmit radiation, particularly low energy x‐rays. Its actual usage has been in nuclear weapons and as a neutron reflector in high flux test reactors. A small beryllium addition produces strong effects in several base metals, eg, in copper and nickel this alloying element promotes strengthening, but no alloy with commercial importance approaching these dilute alloys has emerged. Wrought copper–beryllium alloys rank high among copper alloys in attainable strength. Applications include uses in electronic components, electrical equipment, control bearings, housings for magnetic sensing devices, and resistance welding systems. A variety of copper–beryllium casting alloys exhibit castability advantages. Casting alloys are used in molds and cores for plastic molding, and in undersea, aerospace, sports equipment, and jewelry applications. Nickel–beryllium alloys are distinguished by very high strength and high resistance to fatigue. Wrought nickel–beryllium is used in mechanical, electrical, and electronic components that must exhibit good spring properties at elevated temperatures. Examples include thermostats, bellows, as well as pressure‐sensing diaphragms. Small additions of beryllium to aluminum systems are known to improve consistency. Applications include aircraft skin panels and aircraft structural castings in alloy A357. Beryllium and aluminum are virtually insoluble in one another in the solid state. The potential therefore exists for an aluminum–beryllium metal matrix composite. At least one wrought composite system with nominally 62 wt % Be and 38 wt % Al has seen limited use in aerospace applications.