Influence of Parameter Variations on WC-Co Splat Formation in an HVOF Process Using a New Beam-Shutter Device

The formation of single splats is the foundation for any thermal spray coating. Therefore, this study focuses on the investigation of single splat morphologies to determine the influence of spray parameters on the morphological distribution of particles inside the flame. A new method to create a footprint of a spray jet with an extremely short exposure time was used. The resulting field of splats enabled the assignment of each splat to its radial position in the spray jet. The footprints were analyzed and the quantities and morphologies of the splats were correlated to particle in-flight measurements and coating properties. A strong correlation between the particle velocity, the percentage of the so-called pancake-like splats, and the porosity of the coating could be revealed. The influence of the particle temperature was found to be of minor importance to the splat form and the porosity of the coatings. Still, the particle temperature had a good correlation with the coating hardness and the dissolving of the WC. Measurements of the splat size in different areas of the footprints revealed that the percentage of splats larger than 40 μm in diameter was generally higher in the center of the footprint than in the outer regions.