Exploring three approaches of carbon addition to WC-Co feedstock to mitigate in-flight carbon loss

In contrast to sintered hardmetal/cemented carbide production, thermal spraying occurs in a much more oxidising environment and at a higher temperature, where it is not possible to control the carbon potential to the levels required to retain the desired high carbon content carbide phases. In-flight oxidation of the carbides, or more readily the carbon dissolved within the molten binder, reduces the powder carbon content, resulting in the formation of deleterious sub-carbides exhibiting poorer wear characteristics. This work presents the preliminary results from three conceptual approaches to enrich a WC-17wt%Co feedstock powder with carbon, in an attempt to compensate for that lost in flight such that the desired carbide phases are retained in the coating: 1) Decomposition of sugar to carbon within the WC-17Co powder internal porosity 2) Addition of nano-carbon particles to milled WC-17Co via spray drying followed by sintering 3) Addition of milled Ni/carbon particles to milled WC-17Co via spray drying followed by sintering The powder and coating compositions and microstructures were contrasted with those heat treated at 950-1000°C, which were assumed to have come to equilibrium, to assess the effectiveness of the carbon additions on mitigating carbon loss during spraying. The postulated mechanism of response are discussed.