Improving the Wear Behavior of WC-CoCr-based HVOF Coating by Surface Grinding

WC-CoCr-based high velocity oxy fuel (HVOF) coatings are being used for several components which are prone to severe erosion or abrasion. In this study, the HVOF coating was applied by liquid fuel-based equipment. These coated samples were subjected to surface grinding of various depths (100, 200, and 300 mu m). Hardness test after surface grinding showed that the coating hardness increased by 33% after grinding to a depth of 200 mu m (1472 Hv). The residual stress after different depths of grinding was measured using x-ray diffraction. It showed that the compressive residual stress of coating increased with grinding. Increase in hardness of the coating (after grinding) is believed to be due to the increase in compressive residual stress. The abrasive wear resistance increased after grinding to a depth of 100 mu m thickness and remained constant during successive grinding. In contrast, the erosive wear resistance increased the most when the grinding thickness was 200 mu m. It is concluded that the surface grinding of coatings helps in increasing abrasive and erosive wear resistance. The increase in microhardness of the coating is believed to be the reason for high wear resistance. SEM studies of worn out surface show carbide grain pull out due to removal of softer phase, i.e. cobalt and chromium, and is followed by tungsten carbide grain pull out.