Single-phase material bonding allows precise control of the composition.
Cast aluminium, tool manufacturing and radiation shielding.
Tungsten alloys (WNiFe / WNiCu) are used because of their corrosion resistance against molten metal and high thermal conductivity for chill-mould casting processing of aluminium. Yet, also in tool manufacture and for shielding from alpha and gamma radiation, the heavy metal with its density comparable to gold is indispensable. However, 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 enable the use of tungsten for those more demanding geometries and thus to increase the efficiency and longevity of the components, Bayerische Metallwerke GmbH, which belongs to the Traunstein-based Gesellschaft für Wolfram Industrie mbH, has developed a new manufacturing process for the tungsten alloys WNiFe and WNiCu and patented it in early 2021. This is characterised by the fact that 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 the field of cast aluminium,” says Nabil Gdoura, research and development engineer at Bayerische Metallwerke GmbH.
“The very high density of 19.25g/cm3 in its pure form also makes it a good alternative to the harmful lead, which is still used for radiation shielding in medicine, for example.”
In the case of casting moulds, also known as chill-moulds, used in aluminium processing, the aim is often to have long but at the same time very thin and sometimes conically shaped cooling channels of less than 1mm in diameter in order to ensure the most uniform and rapid heat dissipation possible.
Otherwise, the material quality of the end product can be adversely affected by the formation of cracks. Such precise and sometimes curved shapes are impossible to model from the hard heavy metal, whose extremely high melting point is between 3 387 and 3 422 °C, using conventional machining or forming processing techniques. Therefore, for these complex components for the purposes mentioned, it has so far been necessary to switch to hot-work steel, which can be brought into almost any desired shape with the help of 3D printing techniques.
New tungsten alloy in powder form suitable for 3D printing
After completing the two-year development phase, Bayerische Metallwerke applied for a patent for their new manufacturing process for a tungsten alloy product and its further use at the beginning of 2020, which was finally granted in January of this year.
“The special feature of our tungsten-nickel-iron alloy is that we obtain it in the form of a pre-alloyed powder,” explains 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.”