| Abstract: |
WC-Co-Cr thermally sprayed coatings are widely used in wear resistant applications due to their excellent tribological properties. The use of nanoscale WC grain or finer feedstock particle are two possible methods of improving the properties and performance of WC-Co-Cr coatings further. Previous work has shown that reducing the WC grain size to the nanoscale can increase hardness and improve wear resistance; however, both the nanostructured and finer powders are more susceptible to decarburisation, leading to the presence of undesirable phases that reduce the coating performance. Finer powders are being pursued for the development of coating internal surfaces, as less thermal energy is required to melt the finer powder compared to coarse powders, permitting spraying with a shorter nozzle and smaller stand-off distances. Three WC-10Co-4Cr coatings, with two different particle size and two different carbide grain sizes, were sprayed using a next generation high velocity oxy-air fuel (HVOAF) thermal spray system developed by Monitor Coatings Ltd., UK. The powder and coating microstructure were characterised using XRD, SEM and EDX. Vickers microhardness, porosity and fracture toughness were also studied, and dry sliding wear performance was investigated using a ball-on-disc tribometer with a WC counter-body. This article will discuss the key findings including the decomposition of WC to W2C, porosity and oxidation mechanisms and the effect of stand-off distance on coating microstructure and wear performance when spraying with the next generation HVOAF spray system. The potential applications of HVOAF coatings in future internal spraying setups will be discussed in detail.
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