tungsten alloy

Tungsten wire alloy of tungsten is added to the other elements of the alloy. In metals, the highest melting point of tungsten, high temperature strength and creep resistance and thermal conductivity, electrical conductivity and electron emission properties are better than the material, in addition to a large number of alloys for the manufacture of additives for carbide and tungsten and its alloys are widely used electronics, electric light industry, but also aerospace, casting, weaponry and other sectors for the production of rocket nozzles, die casting mold, penetrator, contacts, heating elements and insulation screens.
The earliest for the production of incandescent tungsten filament. 1909 U.S. Kuli Ji (WDCoolidge) using tungsten powder pressing, remelting, swaging, made of tungsten wire drawing process, from tungsten production has been growing rapidly. 1913 Langmuir (I.Langmuir) and Rogers (W.Rogers) found thorium tungsten wire (also known as thorium tungsten filament) electron emission performance than pure tungsten, start using thorium tungsten wire, is still widely used. 1922 developed with excellent anti-sagging properties of tungsten wire (called doping does not sag tungsten or tungsten), which is the study of tungsten significant progress. Does not sag tungsten filament is excellent and widely used cathode material. 50 to 60 years, for tungsten alloy conducted extensive exploration and research, hopes to develop in 1930 ~ 2760 ℃ working tungsten alloy, used for making high-temperature aerospace industry components. Tungsten-rhenium alloy which more research. Tungsten smelting and processing forming technology also carried out research, using consumable arc and electron beam melting tungsten ingot obtained and processed by extrusion and plastic products made from certain; but smelt ingots coarse grains, poor plasticity , processing difficulties, finished product rate, thereby melting - plastic processing technology does not become the main means of production. In addition to chemical vapor deposition (CVD method), and plasma spraying can produce very few products, made of tungsten powder metallurgy products are still the primary means.

In the 1950s, China has been able to produce tungsten material. 1960 tungsten smelting, metallurgy and processing carried out research, is now able to produce plate, sheet, foil, bar, pipe, wire and other shaped pieces. Tungsten materials using high temperature, only using the solid solution strengthening methods to improve the high temperature strength of tungsten little effect. However, in the solution based on the further strengthening dispersion (or precipitation) hardening, to greatly improve the high temperature strength, and precipitated with ThO2 HfC particle dispersion strengthening effect is best. At 1900 ℃ or so W-Hf-C system and the W-ThO2 alloys have a high-temperature strength and creep strength. Used below the recrystallization temperature of the tungsten alloy, taking temperature hardening methods, to produce strain hardening is an effective way to strengthen. Such as fine tungsten wire with high tensile strength, deformation rate of 99.999% total processing a diameter of 0.015 mm thin tungsten wire, room temperature tensile strength of up to 438 kg / mm; in refractory metals, tungsten and tungsten alloy plastic - brittle transition temperature maximum. Sintering and melting of the plastic Molybdenum plate polycrystalline tungsten - brittle transition temperature is about 150 ~ 450 ℃ between, resulting in difficulties in processing and use, and the single crystal of tungsten is below room temperature. Tungsten material in the interstitial impurities, microstructure and alloy elements, and plastic processing and surface state, the plastic timber tungsten - brittle transition temperature has a significant impact. In addition to tungsten rhenium can significantly reduce the plastic timber - brittle transition temperature, the other alloying elements on the lower plasticity - brittle transition temperature have little effect (see the metal reinforcement). Poor oxidation resistance of tungsten oxide, molybdenum similar characteristics and, above 1000 ℃ volatile tungsten trioxide will occur, resulting in "catastrophic" oxidation. Therefore, high temperature tungsten materials must be used in a vacuum or inert atmosphere protection, if used in high temperature oxidizing atmosphere, you must add a protective coating.

According to different purposes, tungsten carbide alloys are divided into high proportion alloy, metal sweating materials, contact materials, electronics, and electric light materials.

Tungsten doped tungsten powder is added in about 1% of silicon, oxides of aluminum and potassium in the vertical melt (from resistance sintering) process, volatile additives hydroxide, the formation of pores in the material, the trailing edge of the processed hole axially elongated; annealed to form elongated hole parallel to the filament axis dispersed bubbles line, this dispersion foam bubbles known as potassium. Potassium tungsten bulbs impede lateral grain growth, improve anti-sagging properties of high-temperature tungsten, but also to improve the room temperature ductility after recrystallization, help around the wire and transport storage. China tungsten-doped high-temperature creep values ​​by WAl1, WAl2, WAl3 three kinds of grades. In the W-ThO2 alloy, since the added amount of thermal stability, good dispersion of the particles ThO2, not only can reduce the electron work function, can inhibit the grain growth of tungsten, the material has a high recrystallization temperature, excellent high-temperature strength and creep resistance. Tungsten-thorium alloy is widely used in not only the thermal electron emission material, and is an excellent electrode material.

Tungsten-rhenium alloys, rhenium addition, not only can improve the strength of the material, to improve the recrystallization temperature of about 200 ~ 400 ℃, the secondary recrystallization good plasticity, grain growth is slow, and can significantly reduce plastic - brittle transition temperature. Added if more than 30% of rhenium, it will damage the alloy processing performance. Tungsten-rhenium alloy also has a high thermoelectric power, at 2200 ℃, its thermoelectric power linear relationship with temperature. Tungsten-rhenium thermocouples measure the temperature up to 3000 ℃, is excellent high temperature thermocouple materials