Plasma spheroidization of metal and ceramic powders

The paper presents the results of plasma spheroidization of metal and ceramic powders. The aim of the study was to conduct a comparative analysis of two methods for feeding powders into a plasma jet – under the nozzle section (plasma torch F-4) and along the axis of the plasma jet (plasma torch PM-1). Metallic (Cu, NiCr) and ceramic (Al2O3, ZrO2) powders were used as objects of research. To implement the spheroidization process, a specialized water-cooled reactor has been developed that provides controlled cooling of molten particles. Numerical modeling of thermal processes in the reactor confirmed the efficiency of the cooling system: the stationary thermal regime is established 286 seconds after the start of operation of the plasma torch, and the increase in the temperature of water in the reactor, measured experimentally, is consistent with the data obtained by calculation and is 5 °C. It has been established that the PM-1 plasma torch provides homogeneous and finely dispersed powders, however, when processing materials with a low melting point (copper), the powder begins to melt in the inlet channel of the plasma torch, settles on the walls of the nozzle and, over time, clogs it. Spheroidization with the supply of powder under the nozzle section makes it possible to process any materials, however, larger particles with a wide granulometric distribution are formed, especially when processing refractory powders. Based on a comprehensive analysis of the microstructure and granulometric composition of spheroidized powders, technological recommendations have been formulated for choosing the type of plasma torch depending on the required powder properties: the PM-1 plasma torch is preferred for obtaining homogeneous fine powders, and the F-4 plasma torch is preferred for processing low-melting materials and ensuring the maximum degree of spheroidization.