Improvements in hardness and wear resistance of thermally sprayed WC-Co nanocomposite coatings

In this study, a porous spray-dried WC-Co nanocomposite powder has been modified by a protective Co surface layer, and then high velocity oxyfuel sprayed onto a substrate to form a coating. The WC-Co nanocomposite coatings from spray-dried powder and Co-coated powder have been investigated in terms of microstructural features, WC decomposition, porosity, hardness and wear resistance. The microstructure of both as-sprayed WC-Co coatings comprised a layer structure built up of many individual splats, and contained retained WC and large amounts of non-WC phases. The Co-coated powder promoted coarser size of splats, lower degree of WC decomposition and higher retained carbon content in the coating, compared to the spray-dried powder, mainly because of a limited powder melting. Improvements in hardness and abrasive wear resistance were obtained from the Co-coated powder coating, and the results were attributed to more retained WC and consequently a lower amount of non-WC phases whose presence is detrimental to wear resistance.