Tungsten alloy
Filament industry tungsten was first used to make incandescent filament. Colegi (W.D.Coolidge) of the United States in 1909 using tungsten powder pressing, remelting, rotary forging, wire drawing process to make tungsten wire, since then tungsten wire production has been rapid development. Since the discovery of tungsten thorium wire (also known as thorium tungsten wire) emitting electron performance better than pure tungsten wire in 1913 by lanmere (I.Langmuir) and rogers (W.Rogers), the use of tungsten thorium wire has begun and is still widely used. In 1922, a tungsten wire with excellent droop resistance (called doped tungsten wire or not drooping tungsten wire) was developed, which is a major advance in the study of tungsten wire. not droop tungsten wire is widely used as an excellent filament and cathode material. W-based alloys ~ been extensively explored in the 1950s and 1960s in the hope of developing tungsten alloys capable of working in 1930~2760℃ for the manufacture of high-temperature resistant components for use in the aerospace industry. There are many researches on tungsten alloy. The melting and forming technology of tungsten has also been studied. Tungsten ingots are obtained by self-consumption arc and electron beam melting, and some products are made by extrusion and plastic processing. However, the melting-plastic processing technology has not become the main production method because of its coarse grain size, poor plasticity, difficult processing and low yield. Besides chemical vapor deposition (CVD method) and plasma spraying can produce very few products, powder metallurgy is still the main means of manufacturing tungsten products.
Plate Industry China was able to produce tungsten wire in the 1950s. The melting, powder metallurgy and processing processes of tungsten were studied in the 1960s and have been able to produce sheet, sheet, foil, bar, pipe, wire and other special-shaped parts. High temperature materials The use temperature of tungsten material is high, and the effect of solid solution strengthening method is not great to improve the high temperature strength of tungsten. On the basis of solid solution strengthening, dispersion (or precipitation) strengthening can greatly improve the high temperature strength, so that the strengthening effect of ThO2 and precipitated HfC dispersion particles is the best. W-Hf-C and W-ThO2 alloys have high temperature strength and creep strength around 1900. Tungsten alloys used below recrystallization temperature are effectively strengthened by using the method of warm work hardening to produce strain strengthening. If the thin tungsten wire has high tensile strength, the total processing deformation rate is 99.999% and the diameter is 0.015 mm, the tensile strength can reach 438 kg / mm at room temperature Among refractory metals, tungsten and tungsten alloys have the highest plastic-brittle transition temperatures. the plastic-brittle transition temperature of the sintered and melted polycrystalline tungsten material is about 150~450℃, resulting in difficulties in processing and use, while the single crystal tungsten is lower than room temperature. interstitial impurities, microstructure and alloying elements in tungsten materials, as well as plastic processing and surface state, have a great influence on the plastic-brittle transition temperature of tungsten materials. Except that the plastic-brittle transition temperature of tungsten can be reduced obviously, the other alloying elements have little effect on reducing the plastic-brittle transition temperature (see metal strengthening). tungsten has poor oxidation resistance, and the oxidation characteristics are similar to molybdenum. at more than 1000℃, tungsten trioxide volatilizes to produce "disastrous" oxidation. Therefore, tungsten materials must be used at high temperature under the protection of vacuum or inert atmosphere, if used in high temperature oxidation atmosphere, must be added protective coating.
