Burnishing with Grinding Wheel-Shaped Alloy Tool and Its Effect on Surface Integrity and Erosion Behavior of WC-10Co-4Cr HVOF Coating

High-velocity oxy-fuel (HVOF) thermal spray cermet coatings have shown good resistance to erosion-corrosion. High level of porosity on the coating surface hinders the erosion performance, particularly at high particle flux. The work in this paper aims to investigate the influence of burnishing with a grinding wheel-shaped alloy tool, on the surface integrity and solid particle erosion (SPE) behavior of WC-10Co-4Cr high-velocity oxy-fuel (HVOF) thermal spray coating on SS 304. The normal and tangential forces were measured during the burnishing process with the help of a dynamometer. The tangential forces applied by the burnishing tool helped in the flow of plastically deformed surface peaks of the coating. A larger normal force component enforced by the burnishing tool helped to push them into the nearby valleys and the local frictional heat helped to plastically deform them. The burnishing process resulted in large reduction in surface porosity and increased micro-hardness. The optical surface profiles exhibited a major fall in the surface roughness after burnishing. The effect of the burnishing process could also be seen under the coating surface as a decrease in porosity and increase in micro-hardness in the cross-section. As compared to the as-sprayed surface, larger compressive residual stresses, as measured through XRD, were also observed in the burnished surface. The room- and high-temperature SPE weight loss in air-jet erosion testing, at oblique and normal impact angles, improved by about three times after burnishing. The morphology of the surfaces after SPE was studied through SEM micrographs. This indicated that the reduced porosity and higher compressive residual stresses after burnishing provided large improvement in the erosion performance.