Spheroidization of Alumina Powders for Additive Manufacturing Applications by DC Plasma Technology

Alumina is the most widely used oxide ceramic, and its applications are widespread in engineering and in biomedical fields. Its spheroidization was performed by a prototypal direct current (DC) thermal plasma, which was designed and installed at ENEA, investigating surface morphology, particle size distribution, crystallinity, spheroidization, and reactivity. Features such as morphology and porosity significantly influence the flowability of the powder on the printer bed and, consequently, the density of the printed parts. It has been reported that spherical powder shape is highly recommended in additive manufacturing (AM) due to its superior flowability compared to other shapes whose interaction between powder particles results in poor flowability. In this paper, the spheroidization process of alumina powders using two different DC plasma powers and two kinds of secondary gas is reported. The average value of the circularity of the powders, after plasma treatment, has always been greater than or equal to 0.8 with the degree of the spheroidization over 90% at high power. The best process parameters of the thermal plasma were properly selected to produce spherical powders suitable for AM applications, and powders with high circularity were successfully obtained. Forming, debinding, and sintering tests were performed to verify the processability and the densification of produced powders, with good results in terms of density (97%).