Morphological characterization and scaling behaviour of WC coatings deposited by HVOF thermal spray

We report experimental results on the morphological characterization of WC coatings deposited by High-Velocity-Oxygen-Fuel (HVOF) thermal spraying technique. Optical microscopy has been used to characterize film microstructure from the millimeter down to the micrometer scale; surface roughness and correlation length have been estimated as a function of film thickness. We have observed that analysed specimens display a self-affine morphology with Hurst exponent H=(0.33±0.05), in agreement with the scaling behaviour associated to the Kardar - Parisi - Zhang stochastic growth equation and to discrete ballistic deposition models. Our findings suggest that the introduction of scaling arguments within refined theoretical frameworks, realistically treating local splats interactions, could allow to directly predict the morphological evolution of coatings, partially overcoming the intrinsic complexity of the HVOF thermal spray process.