The manufacturing value of tungsten alloys is found in their corrosion resistance against molten metal and high thermal conductivity for chill mould casting processing of aluminium. Yet, because it is a heavy metal, with a density comparable to gold, tungsten is highly valued for tool manufacturing and for shielding from alpha and gamma radiation.
Note, however, that at around 3 400°C, tungsten has the highest melting point of all chemical elements and is therefore very difficult to work with, as well as due to its Mohs hardness of 7.5. As a result, components with more complex shapes, such as curves or conical bores, often have to be switched to hot-work tool steel, which is easier to form.
In order to make tungsten available for use for those more demanding geometries, and thus to increase the efficiency and longevity of the components to be formed, Bayerische Metallwerke GmbH has developed and patented (2021) a new manufacturing process for the tungsten alloys WNiFe and WNiCu. This process is noteworthy because the multi-phase mixed crystal alloy is obtained in a powder form that is suitable as a starting material for 3D printing and coating processes.
“Due to its resistance to corrosion and erosion from molten metals, as well as its excellent thermal conductivity, tungsten is the material of choice in aluminium casting processes,” explained Nabil Gdoura, research and development engineer at Bayerische Metallwerke. “The very high density of 19.25 g/cm3 in its pure form also makes it a good alternative to (toxic) lead, which is still used for radiation shielding in medicine, for example.”
In the particular case of moulds used for aluminium casting, frequently the designer aims to establish long but at the same time very thin and sometimes conically shaped cooling channels, less than 1 mm in diameter, in order to ensure the most uniform and rapid heat dissipation. Otherwise, the material quality of the end product may be adversely affected by crack formation.
Tungsten alloy powders. Following a two-year development phase, in early 2020 Bayerische Metallwerke made a patent filing for its new manufacturing process for a tungsten alloy product and its further use. The patent was finally granted in January 2021.
“The special feature of our tungsten-nickel-iron alloy is that we obtain it in the form of a pre-alloyed powder,” explained Dr.-Ing. Hany Gobran, research and development manager at Bayerische Metallwerke and inventor of manufacturing technology. “This is suitable as a starting product for 3D printing and coating processes.”