Tungsten Rhenium Alloy
The alloy based on tungsten with rhenium is a kind of tungsten alloy. The typical rhenium contents in the alloy are 1%, 3%, 5%, 10%, 20%, 25% and 26%, etc. Microcracks are often formed on the interface of tungsten. The propagation of these microcracks is an important reason for the fracture of tungsten. It is easy to form twins in W-Re alloy during deformation, which reduces stacking fault energy and grain boundary impedance of dislocation movement, which leads to the increase of dislocation mobility and the softening of tungsten solution. This phenomenon is called rhenium plasticizing effect. In the series of W-Re alloys, the plasticizing effect of rhenium is obvious at low rhenium concentration, and decreases at high rhenium concentration.
Performance tungsten rhenium alloys have a series of excellent properties, such as high melting point, high strength, high hardness, high plasticity, high recrystallization temperature, high resistivity, low vapor pressure, low electron work of escape and low plastic brittle transition temperature. In addition to the above properties, the low rhenium alloy and the high rhenium alloy wire are matched to form a thermocouple with high thermoelectric potential.
There are two preparation methods of W Re alloy: powder metallurgy method and melting method. The powder metallurgy process for producing W-Re alloy is as follows: preparation of W-Re prealloyed powder → hydrogen reduction → pressing (die pressing or isostatic pressing) → sintering (vertical melting sintering or medium frequency induction sintering) → pressure processing (including extrusion, rolling, rotary forging and wire drawing). Tungsten and rhenium prealloyed powders are prepared by solid solid method (mixed tungsten powder with rhenium powder, tungsten oxide powder and ammonium rhenium), solid liquid method (mixed tungsten powder with ammonium rhenate solution, tungsten trioxide and ammonium rhenate solution), liquid liquid method (ammonium tungstate solution and ammonium rhenium solution mixed by spray drying or other methods). The tungsten rhenium alloy powder reduced by hydrogen can be formed by mechanical pressing, steel die pressing or isostatic pressing (the density of compact is uniform). W-Re alloy bars with relative density of 92% - 95% can be obtained by direct electric vertical melting sintering or indirect medium frequency induction sintering. Isostatic pressing and medium frequency induction heating sintering can obtain the best quality billet, and its uniformity and consistency are the best among all production methods.
Application tungsten rhenium alloys are mainly used as structural materials in high temperature field and widely used in electronic technology, nuclear technology, aerospace technology and temperature measurement technology. At present, there are three most widely used aspects: (1) low rhenium alloy wire and high rhenium alloy wire are matched to form a thermocouple, which has a wide temperature range (0-2500 ℃), high thermoelectric potential, fast response speed and good corrosion resistance. Therefore, tungsten rhenium thermocouple wire is widely used in temperature measuring instruments. It is not only used in vacuum, reducing atmosphere and inert atmosphere, but also used to replace platinum rhodium thermocouple in oxidizing atmosphere when anti oxidation measures are taken. (2) Tungsten rhenium alloy bar is cut into round pieces and used as electrical contact material. Its contact resistance is small, arc starting current and arc starting voltage are very small. It has the best arc stability and low arc erosion resistance. It is widely used to replace platinum contact material. (3) Tungsten rhenium alloy wires are widely used as hot wires for electron tubes, picture tubes and light bulbs, which not only improve their reliability, but also greatly prolong their service life.
