Influence of the Spray Angle on the Properties of HVOF Sprayed WC-Co Coatings Using Fine Powders (-10 + 2 µm)

Thermally sprayed WC-Co coatings are widely used to protect tools, parts and machine components against wear. These applications typically feature a high dimensional and shape accuracy which have to be preserved after the coating process. HVOF spraying of fine powders with agglomerate size < 15 µm represents an innovative approach to manufacture nearly dense coatings with very low surface rougness, which can meet highest demands regarding the wear protection even at low coating thicknesses. Therefore, the concept is well-suited for the manufacturing of near net-shape coatings.

Most industrial applications usually posses a complex surface so that a multi-axis robot is necessary to perform the coating operation. Whereas the coating of planar surfaces is well-established and leads to uniform coating characteristics, coating of complex geometries places high demands on the handling operations during the spray process. The major problem represents the limited kinematic of the robot system. Depending on the substrate geometry a perpendicular spray angle cannot always be maintained, leading to a worthening of the coating properties and / or inhomogenous coating thicknesses. In order to improve the coating process, it is fundamentally necessary to understand the influence of the spray angle on the coating properties.

In this study we investigate the influence of the spray angle on deposition rate, the mechanical properties and the microstructure of coatings manufactured by using a fine WC-12Co powder with agglomerate size of -10 + 2 µm and 400 nm carbides in the HVOF process.