Tungsten alloy
Tungsten alloys formed by adding other elements are important refractory metal materials. Thorium tungsten alloy was developed in 1913, anti-sag tungsten wire was invented in 1922, high density tungsten alloy was developed in 1935, and tungsten-rhenium alloy was developed in the 1950s. Tungsten alloy materials are widely used in electronics, electric light source, aerospace, military, machinery and metallurgy, etc.
Tungsten alloying is often achieved by adding certain elements in order to obtain or improve certain properties of tungsten. For example, in order to improve the plasticity of tungsten and obtain good thermoelectric properties for the preparation of high temperature thermocouple, rhenium is added to tungsten to form a series of tungsten-rhenium alloys. In order to obtain comprehensive properties such as high density, high strength, good plasticity and easy machining, nickel and iron or copper are added to tungsten to form a series of high density tungsten alloys. Tungsten can be strengthened by solution, diffusion, precipitation and work hardening. When tungsten material is used at high temperature, when pure solid solution strengthening is not enough, dispersion strengthening or precipitation strengthening can be carried out on the basis of solid solution strengthening (such as adding rhenium to tungsten) to improve high temperature strength, such as diffusion ThO2. And precipitation of HfC enhancement. At 2000 ~ 2500oC, w-Tho2, W-Re-Tho2 and W-Re-Hf-C alloys all have high high temperature strength. It is also an effective way to strengthen tungsten alloy under recrystallization temperature. High temperature tensile properties of some tungsten alloys.
Alloy classification and use according to the different elements added, tungsten alloy is mainly divided into :(1) tungsten baht alloy. Adding rhenium to tungsten can increase the ductility and recrystallization temperature of tungsten alloy remarkably. The elongation of pure tungsten wire or doped tungsten wire is usually only 1% ~ 4%, and its plasticity will decrease after recrystallization annealing. Tungsten-rhenium wire has good plasticity and some tungsten-rhenium alloys still have 25% elongation after proper annealing at high temperature. Tungsten-rhenium alloys also have good high temperature strength and excellent thermoelectric properties. Tungsten-rhenium thermocouple temperature up to 2500oC. The rhenium content in tungsten-rhenium alloy is generally 3% ~ 26%, and rhenium is added to the doped tungsten to form a series of WAl - Re alloys, which are used in electronic tubes, picture tubes, light bulbs, high temperature thermocouples and so on. On the basis of tungsten-rhenium alloy, Hf and C were added to make W-Re-Hf-C alloy by smelting, and the high-temperature stable enhanced phase of HfC was precipitated by precipitation. An artificially dispersed ThO can also be added to tungsten-rhenium alloys using powder metallurgy. W-Re-ThO2 alloy.
(2) tungsten molybdenum alloy (or molybdenum tungsten alloy). Tungsten and molybdenum form a continuous solid solution. These alloys have higher resistivity and better toughness than pure tungsten, generally containing 50% to 80% molybdenum. The alloy is used as vacuum tube hot wire, glass sealing lead wire and spark cutting wire.
(3) High density tungsten alloy. Tungsten is made by adding nickel, copper or nickel, iron and a small amount of other elements. There are two alloy systems W-Ni-Fe and W-Ni-Cu. This kind of alloy adopts liquid phase sintering process, sintering density can reach 17 ~ 18.6 g/cm3. The alloy has good machinability, some of them can be improved by vacuum heat treatment plasticity and strength, after plastic processing, the tensile strength can reach more than 1275MPa. W-Ni-Fe alloy has high strength and ferromagnetism, while W -- Ni -- Cu alloy has low strength and no ferromagnetism. These alloys are used for various inertial components such as gyro rotors, ray shielding materials, die-casting molds, counterweight materials and armor piercing bodies.
(4) Tungsten-copper alloy and tungsten-silver alloy (also known as tungsten-copper material and tungsten-silver material). Because tungsten and silver, copper between insoluble and reaction, so called false alloy. It makes use of the high melting point, high hardness and arc ablation resistance of tungsten and the high electrical and thermal conductivity of copper and silver. General alloy containing copper or silver 1% ~ 50%, the formation of a variety of grades of alloy. These alloys are widely used as electrical contacts, electrical contacts, semiconductor supports and rocket nozzles.
(5) Cerium tungsten alloy, lanthanum tungsten alloy, yttrium tungsten alloy, etc. An alloy formed by adding dispersed oxides of cerium, lanthanum, and yttrium to tungsten (also known as tungsten monooxide material). The oxide content is generally less than 4%, and the specific amount varies with the alloy. This kind of alloy has very good thermal-electron emission property, and has no radioactive material. Thorium tungsten alloy has been widely used as high temperature electrode for argon arc welding, plasma welding and cutting, non-consumable arc furnace, etc.
(6) Thorium tungsten alloy (also known as tungsten-thorium alloy, thorium tungsten material). Tungsten is made by adding 0.4% ~ 4.2% dispersed high temperature stable ThOz to the metallurgical metal. The alloy has high thermal electron emission ability, high recrystallization temperature, excellent high temperature strength and creep resistance. The material is used in tube hot cathode, high temperature discharge electrode and argon arc welding electrode.
Tungsten alloy is mainly produced by powder metallurgy. Firstly, the tungsten powder is fully mixed with alloying element powder or other additive powder, and can also be added in the tungsten oxide powder in the form of nitrate and other compound solution according to the alloy chemical composition. Then, the alloy powder with highly dispersed additives is prepared by evaporation, drying and hydrogen reduction method. Then pressing forming, pre-knot, sintering and other processes into alloy ingots, and ingots of plastic processing can be made into bars, wire, sheet and so on. There is also a process, the first tungsten billet sintering, but retain a certain amount of through hole, and then impregnated copper, silver, and made of "tungsten infiltration of copper", "tungsten infiltration of silver". Another kind of alloy, such as W-Re-Hf-C alloy, is made by electric arc furnace, electron beam furnace smelting.
