Spherical metal powders are essential feedstock for a wide range of Additive Manufacturing (AM) processes. They are usually produced on an industrial scale by gas atomization of liquid melts with high inert gas consumption. Increasing the gas temperature during atomisation offers the potential to significantly reduce gas consumption while maintaining or even improving powder quality. As the gas temperature rises, the gas density decreases, resulting in a lower mass throughput, while the gas velocity and viscosity increase. These effects contribute to the production of smaller particles at higher gas temperatures. Current industrial hot-gas atomization already operates at gas temperatures up to 400°C. However, flow simulations indicate that a further reduction in gas consumption and an increase in gas velocity are possible at even higher gas temperatures [1], contributing to cost reduction, especially when using expensive argon, and a better CO2-balance.

In order to investigate the effect of high gas temperature on the atomization of molten metals, a novel high-temperature Close-Coupled Atomizer (H-CCA) was developed, capable of operating with gas temperatures up to 1000°C. Experimental investigations using the H-CCA configuration demonstrated highly promising results for steel powder production. At a constant gas pressure, a reduction of gas consumption of up to 50% was achieved in the 700°C to 800°C range compared to cold gas atomization. In addition, at a gas temperature of 800°C and 14-16 bar gas pressure, the fine fraction of the powder (<20 μm) increased by 25% to 30%. This is attributed to the reduced gas density and simultaneous increase in gas velocity and viscosity at higher temperatures. Copper powder (CuSn6) generated during hot-gas operation is evaluated to determine particle cooling rates based on measurements of dendrite arm spacing. Numerical flow simulations were performed to analyse in detail gas flow and particle behaviour within the powder plant. The simulated cooling rates are validated against the experimental results, and an existing cooling model is adapted and extended for hot-gas conditions.

This work aims to establish the design principles for future H-CCA systems, including the prediction of median particle sizes and solidification rates, to enable industrial adoption of this highly efficient and resource-saving technology.

References
[1] S. Hussain, C. Cui, L. He, L. Mädler, V. Uhlenwinkel, Journal of Materials Processing Technology, 2020, 282, 116677, https://doi.org/10.1016/j.jmatprotec.2020.116677.