metals Article Plasma Spheroidisation of Irregular Ti6Al4V Powder for Powder Bed Fusion Nthateng Nkhasi 1, *, Willie du Preez 2 and Hertzog Bissett 3   Citation: Nkhasi, N.; du Preez, W.; Bissett, H. Plasma Spheroidisation of Irregular Ti6Al4V Powder for Powder Bed Fusion. Metals 2021, 11, 1763. https://doi.org/10.3390/met11111763 Academic Editors: Marco Mandolini, Paolo Cicconi and Patrick Pradel Received: 3 September 2021 Accepted: 28 October 2021 Published: 2 November 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Mechanical and Mechatronics Engineering, Central University of Technology, Bloemfontein 9301, Free State, South Africa 2 Centre for Rapid Prototyping and Manufacturing, Faculty of Engineering, Built Environment and Information Technology, Central University of Technology, Bloemfontein 9301, FreeState, South Africa; wdupreez@cut.ac.za 3 Applied Chemistry, South African Nuclear Energy Corporation SOC Ltd. (Necsa), Pretoria 0001, Gauteng, South Africa; hertzog.bissett@necsa.co.za * Correspondence: nthatengnp@gmail.com Abstract: Metal powders suitable for use in powder bed additive manufacturing processes should ideally be spherical, dense, chemically pure and of a specified particle size distribution. Ti6Al4V is commonly used in the aerospace, medical and automotive industries due to its high strength-to- weight ratio and excellent corrosion resistance properties. Interstitial impurities in titanium alloys have an impact upon mechanical properties, particularly oxygen, nitrogen, hydrogen and carbon. The plasma spheroidisation process can be used to spheroidise metal powder consisting of irregularly shaped particles. In this study, the plasma spheroidisation of metal powder was performed on Ti6Al4V powder consisting of irregularly shaped particles. The properties of the powder relevant for powder bed fusion that were determined included the particle size distribution, morphology, particle porosity and chemical composition. Conclusions were drawn regarding the viability of using this process to produce powder suitable for additive manufacturing. Keywords: plasma spheroidisation; additive manufacturing; Ti6Al4V powder; powder bed fusion 1. Introduction South Africa has a vision to raise its profile on the global business stage by adding value to its titanium-bearing mineral resource through turning it into metal powder that would be suitable for additive manufacturing (AM). In 2020, South Africa was rated the second largest mining producer of ilmenite (1000 t) and the third largest mining producer of rutile (100 t) in the world [1]. In South Africa, the Council for Scientific and Industrial Re- search (CSIR) built a pilot plant that produces commercially pure titanium powder [2]. The titanium powder is produced in this plant through the continuous stepwise metallothermic reduction of titanium tetrachloride in a molten salt medium. These titanium powders pro- duced at the CSIR are intended to be used in various downstream manufacturing processes, such as AM, powder metallurgy and investment casting. However, the titanium metal powder produced through the CSIR-Ti process is either spongy or crystalline, depending on the process parameters [3]. For use in powder bed fusion (PBF), the metal powder should ideally be spherical, dense and chemically pure. An irregularly shaped particle is less desirable for PBF processes, because it increases the flow time and could reduce the packing density [4]. Powder consisting of spherical particles is usually produced by atomisation methods or plasma spheroidisation (PS) [5]. Titanium alloys primarily stand out due to high specific strength and excellent cor- rosion resistance. This also explains their preferential use in the aerospace sector, the chemical industry, medical engineering and the leisure sector [5]. Titanium and its alloys are well-established for their combination of relatively high strengths, low densities, and Metals 2021, 11, 1763. https://doi.org/10.3390/met11111763 https://www.mdpi.com/journal/metals