Improving the Performance of HVOF Sprayed WC-Co Coatings Using Statistical Design

Abstract

This study reports the statistical optimization of experiments, designed by Taguchi, to improve the wear-resistance of the tungsten carbide/cobalt-based coatings applied using high-velocity oxygen-fuel (HVOF) spraying processes. In this study, a group of needlelike textures appeared in the HVOF WC-Co coatings. The structures were evenly distributed and compacted closely, showing a more dense and homogenous configuration. The coating that formed with a large amount of pores, microcracks and unmolten particles was much looser, and the interface was locally prone to defects. The coatings were obviously not homogenous. Experimental results show that the wear-resistant coatings are highly dense, with an elastic lamellar structure. The tribological properties were significantly improved and the surface textures showed uniformity, in a molten droplet flattened formation. A homogenous, morphological structure, with local small aggregation, was more obvious after HVOF WC-Co coating. Accordingly, it is clear that the surface properties determined proved favorable to the mechanical properties of the WC/Co coatings. In addition, we compared the linear models with the quadric models, using RSM methods, in all the experiments. Statistically, the linear models produced an average error of 8.285％, while the quadric models generated an average error of 1.399％. It is clear that the RSM models successfully fitted the HVOF WC-Co coating process and the quadric models yielded more accurate predictions than the linear models, in most cases. The proposed procedure was applied to HVOF spraying of WC-CO coatings. The results demonstrated its feasibility and its effectiveness in improving the HVOF WC-Co coating.