Plasma spheroidization utilizing a plasma spray gun has been demonstrated for water-atomized stainless steel SUS316L powder. The angular particles were successfully spheroidized, and the D50 size of particles were decreased from 35 μm to 24 μm with 9 kW of processing power and to 15 μm with 17 kW of processing power. It was found that the high processing power of 17 kW generates a significant number of fine particles with the size of under 1 μm. By contrast, the powder formed on low processing power of 9 kW has better flow-ability and low cohesiveness, suggesting that an appropriate processing power exists to form the spherical powder suited for additive manufacturing

Inductively coupled radio frequency (RF) plasma spraying, powered by high-frequency oscillating electrical current, performed an important role in fine powder manufacture. It was used in the present study to prepare fine spherical bioceramic powders of hydroxyapatite (HA) whose chemical composition similar to those of natural bone. The as-sprayed powders consisted of both micron-sized spherical particles and nano-sized particles. In addition to the spheroidization effect, rf plasma treatment led to the decomposition of HA into secondary calcium phosphate phases including tri-calcium phosphate (TCP), tetra-calcium phosphate (TTCP) and calcium oxide (CaO). The microstructure investigation showed that the spheroidized particles were either fully dense or hollow structure with a shell. The reason for the formation of hollow spheres was contributed to the higher density of the solidifying surface layer compared with the molten phase during solidification.