HARD METAL COATINGS FOR INNER DIAMETERS SPRAYED BY HIGH VELOCITY AIR FUEL (HVAF)

Thermal spray techniques are a family of “state of the art” surface engineering processes used to deposit protective coatings on mechanical components. Among thermal spray techniques, HVAF (High Velocity Air Fuel) spraying is a recently developed method, whose performances are very promising. The HVAF coating properties are still under investigation in particular when inner diameters are concerned, since HVAF is a line of sight process. Therefore, the options are either the development of special guns for inner diameters, keeping the optimal 90° spraying angle, or spraying at lower angles with a standard HVAF. Besides, this latter option can be limited by the component diameter and size. The purpose of this master thesis is to study hard metals coatings on inner diameters, sprayed both by an HVAF inner diameter gun (ID7 gun) and a standard HVAF M3 gun. A Design of Experiments (DOE) approach has been used to find the best working parameters for the ID7 gun. Thanks to the DOE results, the best parameters and powder hard metal powder feedstock have been found. The properties of the coatings sprayed with ID7 and M3 guns have been compared investigating their microstructure and wear resistance.