Fabrication of spherical WC–Co powders by radio frequency plasma and heat treatment

Spherical WC–Co powders used for the 3D printing were successful prepared by the radio frequency (RF) plasma and the subsequent heat treatment, using the granulated WC–30Co powders prepared by spray drying method as the raw materials. The effects of RF plasma spheroidization and heat treatment on the powder properties were studied. The results show that, the RF plasma has the remarkable spheroidization effect, and the spheroidization rate of the spray granulation powders can reach 100%. The spheroidized powders show the smooth surface and compact structure, containing a certain number of "Ferrero" particles with the rough surface. The RF plasma treatment can significantly improve the apparent density and flowability of the powders, and causes the serious decomposition of WC and the evaporation loss of Co. There are many harmful phases such as C, W₂C, and Co₃W₃C in the spheroidized powders, and the mass fraction of Co is reduced to 25.80%. The subsequent heat treatment can well control the phase and composition of the spheroidized powders. After the heat treatment at 900 ℃, the phase composition of the WC–Co powders is transformed into WC and Co, and the free carbon content is controlled at a reasonable level. Moreover, the heat-treated powders still maintain the good sphericity, apparent density, and flowability, which are suitable for the 3D printing as the raw materials.