Characterisation of Spheroidised tungsten carbide metco 32c powder using radio frequency plasma

Abstract

Metco 32C is a coarse grey powder, which mostly consists of tungsten carbide and cobalt; with small traces of nickel, chromium, boron, iron silicon and carbon. Metco 32C powder has the role of supporting oxidation and corrosion resistance at high temperatures as well as increasing the hardness of the coated materials. The spheroidal morphology of Metco 32C improves flowability during layer application methods such thermal spraying. There has been a growing interest in the development / improvement of methods producing powders of cast tungsten carbide and other high-melting-point materials of uniform composition, characterised by a high sphericity of the particles and having higher physical-mechanical properties. Spherical particles are generally preferred in the additive manufacturing process as they pack together for uniform powder bed density, better flowability in machinery, eliminate internal cavities and fractures resulting in a better quality of final product. Similarly, thermal spraying processes also require dense, spherical particles to ensure consistency and reproducibility of the feeding mechanism as well as interaction between the feedstock and thermal spraying heat source. The process of transforming irregularly shaped powder particles into spherical shapes is known as the spheroidisation process and this can be achieved by plasma spheroidisation. It was found that the spheroidisation ratio of the powder increased as the plasma plate power increased. A decrease in density was observed as plasma power increased. The spheroidised powders have a smaller particle size distribution (PSD) than the feed powders (un-spheroidised). The XRD results showed that as the plasma plate power increased the WC phase composition decreased, subsequently the phase composition of W2C increased.