Germany-based metal processing company Bayerische Metallwerke GmbH, a subsidiary of Wolfram Industrie, has developed and patented a new material production process specifically for tungsten alloy.
The process is special in that it’s able to yield high-concentration tungsten pre-alloy mixes (WNiFe and WNiCu) in a powder form, enabling the materials to be used in both 3D printing and coating processes. Backed by a two-year development phase, the company believes its new process will pave the way for more complex part geometries made of tungsten, offering new options for applications such as tool manufacturing and 3D printed radiation shielding.
“The special feature of our tungsten-nickel-iron alloy is that we obtain it in the form of a pre-alloyed powder,” explains Dr. Hany Gobran, research and development manager at Bayerische Metallwerke. “This is suitable as a starting product for 3D printing and coating processes.”
Tungsten alloys: useful but stubborn
Tungsten alloys are well-known for their excellent corrosion resistance and high thermal conductivity, making them a perfect candidate for the chill-mold casting of aluminum parts. The heavy metal is also extremely dense, coming in at 19.3 g/cm³. With a density comparable to that of gold, tungsten sees extensive use in tool manufacturing and alpha and gamma radiation shielding in healthcare.
“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. “The very high density in its pure form also makes it a good alternative to harmful lead, which is still used for radiation shielding in medicine, for example.”
Unfortunately, tungsten also has the highest melting point of all chemical elements (3,400°C) and a Mohs hardness of 7.5, rendering it extremely difficult to work with. As such, tungsten parts with more complex geometries such as curves and bores are often just made of hot-work tool steel instead, due to its ease-of-use and 3D printability.
Tungsten alloy production for 3D printing
According to Bayerische Metallwerke, all commercially available tungsten 3D printing alloys to date have been produced with relatively high concentrations of iron and nickel, often without any pre-alloying. Since the melting points of these metals are significantly lower than that of tungsten, high-temperature additive manufacturing processes such as powder bed fusion often result in their uncontrollable evaporation.
The new Bayerische Metallwerke process addresses this issue by pre-alloying the powder mix before processing. By combining all three elements as a multiphase material in each individual powder particle, the composition and distribution of the final alloy can be very closely controlled. As such, the metal can be processed at high temperatures without losing any of the iron, nickel, or copper.
The company states that its new process is capable of producing alloys with 80% – 98.5% (weight) tungsten, 0.1% – 15% nickel, and 0.1% – 10% iron and/or copper, depending on the desired application. With densities of 17 – 18.8 g/cm3, the alloy materials are more than suitable for tungsten’s conventional use cases in aluminum casting, tool manufacturing, and radiation shielding. As a bonus, the patented process also enables the flow behaviour and grain size of the powder particles to be determined.
“The higher the proportion of tungsten in the end product, the more resistant it is to molten aluminium and the better its thermal conductivity,” concludes Gobran. “If, on the other hand, good ductility and mechanical machinability play a greater role, the proportion of tungsten in the alloy can also be reduced accordingly. The composition can therefore always be adapted to the specific application and the respective complexity of the shape.”
Powder production for industrial additive manufacturing
Though it may be in the background, the powder production sector is absolutely crucial for the success of industrial additive manufacturing. Earlier this year, Pyrogenesis, a specialist in plasma atomization technology, announced the successful testing of its Additive Manufacturing NexGen powder production line. Following a strategic decision to delay commercial production, the Montreal-based firm was able to implement improvements and has now tested for batch to batch consistency in its production line.
Elsewhere, Canadian mining and metals firm Rio Tinto recently developed a new steel 3D printing powder using water atomization technology. While it is widely believed that only high-cost gas and plasma atomizers are capable of producing industrial-grade powders, the company’s new steel powder has shown that water atomization is a more affordable route to 3D printing powder production.
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Featured image shows tungsten alloy powders produced by Bayerische Metallwerke. Photo via Bayerische Metallwerke.