Tungsten alloy
Tungsten alloy is an alloy based on tungsten and added to other elements. Among the metals, tungsten has the highest melting point, high temperature strength and creep resistance, as well as thermal, electrical and electronic emission properties. In addition to a large number of applications in the manufacture of cemented carbide and as alloy additives, tungsten and its alloys are widely used in the electronics and electric light source industries, as well as in the manufacture of rocket nozzles, die-casting dies, armour-piercing projectiles, core contacts, heating bodies and heat insulation screens in the aerospace, casting and weapons sectors.
Molybdenum-tungsten alloy An alloy containing two elements, molybdenum and tungsten, including molybdenum-based tungsten alloys and tungsten-based tungsten-molybdenum alloys. The alloy can be formed in any proportion and is a complete solid solution alloy at all temperatures. niobium tungsten alloy A niobium alloy formed by adding a certain amount of tungsten and other elements. tungsten and niobium form unlimited solid solution. Tungsten is an effective strengthening element of niobium, but with the increase of the amount of tungsten added, the plasticity of the alloy will increase the brittle transition temperature, and the grain size will grow significantly. Therefore, in order to obtain the high strength niobium tungsten alloy, the amount of tungsten should be properly controlled, and the elements such as zirconium and hafnium should be added to refine the grain and reduce the temperature of plastic brittle transition. In 1961, the United States developed the Nb-10W-2.5Zr alloy for the space shuttle skin, and then developed into the Nb-10W-1Zr-0.1C alloy. In the early 1970s, China also developed NbWl0Zr2.5 and NbWl0Zr1C0.1 alloys. Carbide Carbide is one of the most common and important forms of tungsten alloy. Different from the previous tungsten alloys, it is tungsten and carbon and cobalt, so it is often called tungsten-cobalt alloy. The most widely used tools in industry are mostly carbide tools, so the tungsten alloy is also called "industrial teeth ". In 1907, a low-nickel tungsten alloy was introduced, which was prepared by mechanical processing, but its application was hampered by its severe brittleness. Until 1909, U.S. General Electric Co.’ s w.D. Coolidge obtained tungsten billet strips by powder metallurgy, and then used mechanical processing to produce tungsten filaments with ductility at room temperature, thus laying the foundation of the tungsten filament processing industry and also laying the foundation of powder metallurgy. However, the "ductile" tungsten alloy showed obvious brittleness after the bulb ignited. in 1913, pintsch invented thorium tungsten filament (tho2 with a content of 1% to 2%), which greatly reduced the brittleness of the incandescent filament. At first, the droop of the filament (see the droop resistance of the tungsten filament) was not an issue, because the filament was straight at this time, but after 1913, Langmuir changed the filament to a spiral filament, so that when the bulb was used, the action of high working temperature and weight made the filament droop, so that both pure tungsten and thorium tungsten could not meet the requirements of use. To solve the problems of tungsten wire droop and short life, in 1917, A. Pacz invented the "non-deformed" tungsten alloy at high temperature. At first, he used a fire-resistant crucible to roast WO3 in the preparation of pure tungsten, and inadvertently found that the tungsten filament spiral made from the tungsten powder obtained from this reduction of WO3, after recrystallization, was unusually mysteriously no longer drooping. subsequently, after 218 repeated experiments verification, he finally found that silicate with potassium and sodium in tungstic acid (wo3• h2o), obtained by reducing, pressing, sintering, processing and so on, formed a rather coarse grain structure after recrystallization, which was neither soft nor anti-sagging, which was the earliest non- pendant tungsten filament. Burs's discovery laid the foundation for the production of non-sagging tungsten filaments until the United States still did not call them "218 tungsten filaments "to commemorate the major discovery. The production process of doped tungsten alloy is lengthy, including several main stages of tungsten smelting, powder metallurgy billet making and plastic processing. Ammonium paratungstate (APT) is usually used as raw material in the production of tungsten-doped alloys. In addition to the classical process of producing ammonium zhongtungstate from tungsten concentrate, the international research of extraction method and ion exchange method was carried out in the 1950s. China also adopted these processes in the 1970s, thus simplifying the technological process and improving the recovery rate of tungsten. Since the 1960s, many countries have adopted blue tungsten oxide doping process instead of tungsten trioxide doping, thus improving the doping effect. the pickling of tungsten powder was started to be used in production in the 1960s, and its main purpose is to wash off the excess dopant, ultrafine powder and some harmful impurities in tungsten powder, thus improving the processing performance and the high temperature performance of tungsten wire. Since 1960s, the method of pore-type rolling has been applied continuously. Hole rolling is to make the blank pass through the hole of a pair of rotating rollers, and reduce the section and extend the length under the action of roll pressure. Although only a few tungsten ores are eventually made into filaments and similar products, the most important scientific and technical implications of tungsten are the conversion of its research to practical applications. the acquired knowledge has invaluable value in new areas of powder metallurgy, especially in the manufacture of cemented carbide.
