Necessity of vacuum annealing of rare refractory metals

Vacuum annealing refers to the process of slowly heating a workpiece to a specified temperature under conditions below one atmosphere, keeping the temperature for a period of time, and then cooling the workpiece to room temperature according to a specified cooling method.

Application of vacuum annealing of rare refractory metals

Metals such as titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), and tungsten (W) are called rare metals because they are rarely found in nature, are sparsely distributed, and are difficult to extract from raw materials. They play an irreplaceable role in certain fields of cutting-edge industries such as high-end processing and manufacturing, electronics, atomic energy, new energy, and aerospace. For example, titanium has a low density and high specific strength, and is widely used in the manufacture of spacecraft. Some compounds and alloys of niobium (niobium-titanium and niobium-tin) have a high superconducting transition temperature and are widely used in the manufacture of various industrial superconductors, such as superconducting generators, accelerator high-power magnets, superconducting magnetic energy storage devices, and nuclear magnetic resonance imaging equipment. Niobium is also a very good “bioadaptive material”. Niobium sheets can be used to make up for skull damage, niobium wire can be used to suture nerves and tendons, niobium bars can replace broken bones and joints, and niobium yarn or niobium mesh made of niobium wire can be used to compensate for muscle tissue, etc. Tantalum can be used to manufacture high-power capacitors, transmitting tube electrodes, etc. in the electronics industry. Tantalum and niobium have good acid and alkali corrosion resistance. In the chemical industry, they can be used to make cooking vessels, heaters, coolers and material vessels; their high temperature strength is high, and they can be used to make heat-resistant engine parts for space shuttles, rockets, such as combustion chamber combustion ducts, turbo pumps, rocket accelerator nozzles, etc. Molybdenum and tungsten have high electrical conductivity, small expansion coefficient, and good thermal conductivity, and are suitable for electrode materials and electric vacuum components. Molybdenum wire is an ideal electrode wire for electric spark wire cutting machine tools, and tungsten wire is used to manufacture tungsten poles for welding machines, direct-heated cathodes and grids for electronic oscillator tubes, cathodes for high-voltage rectifiers, and side-heated cathode heaters in various electronic instruments. Molybdenum and tungsten have low high-temperature saturated vapor pressure and less evaporation, and are often used to manufacture electric heating elements and structural materials for vacuum high-temperature furnaces. Molybdenum can be used up to 2000°C in nitrogen, and molybdenum wire can be used close to the melting point in hydrogen and decomposed ammonia. Tungsten wire and tungsten rod can be used up to 3000°C when working in hydrogen gas, inert gas or vacuum. The common feature of the above metals is that they have high melting points and their processing often needs to be carried out at high temperatures, so vacuum annealing becomes a necessary process in their processing. The melting points of each metal are shown in the table.

Necessity of vacuum annealing of rare refractory metals

Molybdenum, tungsten, tantalum, cobalt, vanadium, zirconium and other metals have high melting points, are easily oxidized, and are easily contaminated by refractory materials. They have high strength and hardness during processing. If they contain gases such as hydrogen, oxygen, and nitrogen, the ductility of the material will deteriorate. In order to turn them into profiles, they must be softened after vacuum annealing before pressure processing.

Vacuum Annealing Furnace