Development history of tungsten alloys
In 1907, a low-nickel tungsten alloy was produced by machining, but severe brittleness hindered its application. until 1909, kuliqi (w.D.Coolidge) of general electric company of the united states obtained tungsten billet strips by powder metallurgy, and then produced tungsten wire with ductility at room temperature by mechanical processing, thus laying the foundation of tungsten wire processing industry and powder metallurgy.
however, this "ductile" tungsten alloy exhibits obvious brittleness after light bulb ignition. Pinch (Pintsch) invented thorium tungsten wire (1%~2% in ThO2) in 1913, which greatly reduced the brittleness of incandescent filament. at first, the droop of the filament (see the droop resistance of the tungsten filament) was not a problem, because the filament at this time was straight, but after 1913, lanmere (Langmuir) changed the straight wire to spiral wire, so that when the bulb was used, the action of high working temperature and deadweight caused the filament to droop, so it was difficult for both pure tungsten and thorium tungsten to meet the requirements of use.
In order to solve the problems of tungsten wire sagging and short life span, in 1917, berth (A.Pacz) invented tungsten alloy with "no deformation" at high temperature. Originally, he used fire-resistant crucible roasting in the preparation of pure tungsten WO3, inadvertently found that the tungsten wire spiral made of tungsten powder reduced by this WO3, after recrystallization, it unusually mysterious and no longer drooping. subsequently, after 218 repeated experimental verification, he finally found that silicate with potassium and sodium added to tungstate (WO3•H2O), obtained by reduction, pressing, sintering, processing, etc., recrystallized to form a rather coarse grain structure, which is neither soft nor droop resistant, which is the earliest do not droop tungsten wire. the discovery of beth laid the foundation for the production of non-proliferative tungsten wire, which until the united states still called "218 tungsten wire ", in memory of this major discovery of beth.
The production process of doped tungsten alloy is lengthy, including several main stages of tungsten smelting, powder metallurgy billet making and plastic processing. ammonium secondary tungstate (APT) is usually used as the raw material for the production of doped tungsten alloys. in addition to the traditional classical process, extraction and ion exchange methods were carried out internationally in the 1950s from tungsten concentrate. china also adopted these processes in the 1970s, thus simplifying the process flow and improving the recovery rate of tungsten. Since the 1960s, many countries have adopted tungsten blue doping process instead of tungsten trioxide doping, thus improving the doping effect. the pickling of tungsten powder was applied to production in the 1960s. the main purpose is to wash away the excess dopants, ultrafine powder and some harmful impurities in tungsten powder, so as to improve the processing performance and the high temperature performance of tungsten wire. Since the 1960s, the hole rolling method has been applied continuously. Pore rolling is to make the blank pass through the pass of a pair of rotating rolls, reduce the section and extend the length under the action of roll pressure. Although only a few tungsten ores are eventually made into filament and similar products, the most important scientific and technical significance of tungsten is the transformation of its research results to practical applications. The acquired knowledge has invaluable value in new fields of powder metallurgy, especially in the manufacture of cemented carbides.
