Processing and treatment of tungsten and its alloys
Recently, the research team from the University of Bath recently published the latest research progress on the processing and treatment of tungsten (W) and its alloys. W belongs to group 6 of the periodic table, together with molybdenum, chromium and boron. It is a refractory metal (the highest of all known pure metals), with extraordinary heat resistance and wear resistance. In addition to its very high melting temperature, W is known for its high density, high elastic modulus, high thermal conductivity, and excellent mechanical properties at high temperatures. W is an ideal material for high temperature structures in fusion energy and other applications.
The demand for electricity is growing at an unprecedented rate, and the total final energy consumption of electricity is expected to increase from 19% in 2018 to 24% in 2040. Under the influence of climate change, some countries have set the goal of net zero emissions in the middle of this century to achieve the goal of the 2015 Paris Climate Agreement. However, according to the recent emission gap report of the United Nations Environment Programme (UNEP), these ambitious goals are not without obstacles. Even if these goals are achieved, the global temperature will still rise by more than 3 ℃ from the pre industrialization level in this century, which will far exceed the 2 ℃ stipulated in the Paris Agreement. It is urgent to carry out technological innovation and sustained policy intervention on a global scale to reverse this trend.
Since the 1950s, nuclear fission has been widely used as a source of electricity. On the other hand, nuclear fusion has its inherent advantages, helping to encourage its application in modern energy infrastructure. Among other benefits, nuclear fusion will not cause harmful emissions, and its reaction can be better controlled. The careful design of the reactor leaves room for efficient, cheap and safe energy. In order to achieve reliable and large-scale nuclear fusion, technological and scientific progress is required in manufacturing radiation resistant materials that can withstand extreme conditions in reactors.
W's rich history, from the discovery of its ores and compounds to the later important technological discovery, stimulated the early widespread application. The discovery of W mineral can be traced back to tin mines in Saxony Bohemia and Cornwall in the Middle Ages, far earlier than the separation of the element itself. Although the separation of W was first proposed by Torbern Bergmann in 1781, Juan Jos é de Elhuyar and his brother Fausto prepared this metal by reducing tungstic acid with charcoal powder in 1783. This metal is also named wolframite, which is still its official name in German and Swedish today.
The earliest application of W is to produce special steel as an alloy element. Soon, it gained a prominent position as the filament of the incandescent lamp, replacing the carbon filament. Since then, this material has been widely used in various fields, including aviation, automobile, electronics, medicine, military, chemistry and sports. Its applications include heating wires, electronic transmitters, radiators, heating elements and radiation shielding in high-temperature furnaces, kinetic energy penetrators, balance weights in racing cars and aerospace, rotors in the clock industry, heavy electrical contact materials and welding, plasma and X-ray electrodes.
Although W's properties are beneficial to its application, W's ductility and high melting point also lead to some challenges in large-scale manufacturing of components made of W and its alloys, which limits the production of these complex geometric shapes. In this paper, the researchers emphasized that processing methods, such as powder metallurgy and additive manufacturing, can produce components that are similar to meshes. However, this requires post-processing techniques to complement these methods. They explored and discussed the different manufacturing methods of W in depth, and identified the challenges and gaps related to each method. It includes traditional and unconventional processing technologies, as well as research on improving the ductility of tungsten by various methods, such as alloying, thermodynamic treatment and grain structure refinement.
