Numerical Analysis of Radio-Frequency Inductively Coupled Plasma Spheroidization of Titanium Metal Powder Under Single Particle and Dense Loading Conditions

Abstract

In order to allow more practical prediction of RF (radio-frequency)–ICP (inductively coupled plasma) spheroidization results of titanium metal powder, numerical analyses under single particle and dense loading conditions were carried out and the results were compared. First, both of the numerical results for Ar inductively coupled plasma with the power level of 30 kW revealed that the injected particles can experience not only spheroidization by melting, but also size reduction by evaporation. In addition, this size reduction was found to strongly depend on the initial sizes of the injected particles, due to the relatively short heating time. For example, the 100 µm Ti particles were computed to hardly experience size reduction by evaporation regardless of feeding rates. However, relatively small Ti particles < 100 µm can be rapidly heated up to boiling points during the short flight of plasma, resulting in the size reduction by the surface evaporation. In particular, numerical results under dense loading condition showed that the final sizes of these small Ti particles can be changed depending on the feeding rate. For example, a single 60 µm Ti particle was calculated to be a 51 µm spherical Ti particle due to the excessive heating. However, with the increase of feeding rate up to 1.0 kg/h, the final sizes of the as-treated Ti powder could be improved to 55 µm due to the plasma temperatures decreasing through complicated plasma–particle interactions. By predicting the relationships between the feeding rates and the initial diameters of Ti powders at a given plasma power level, numerical modellings under single particle and dense loading conditions can help in optimizing the RF–ICP spheroidization process of titanium metal powder.