High velocity spray deposition of WC cermets by an air-oxygen controlled combustion process

HVOF processes represent the state of art for the spray deposition of wear and corrosion resistant coatings since their supersonic gas velocities in combination with moderate flame temperatures allow the deposition of optimal coatings with very high bond strengths, fine surface finishes and low oxide levels. However, new generation coating materials (fine powders), stringent quality requirements and the high productivity demanded by the industry, push the HVOF technologies to their limits. Recently, a novel air-oxygen controlled high velocity combustion process has been development by Tecnalia. The system operates within the supersonic regime using a broad range of fuel/oxidant ratios thanks to the use of air-oxygen mixtures and a carefully designed gun. Extremely low flame temperatures can be achieved while keeping a supersonic flow of combustion products, thus allowing the solid state deposition of almost all industrially relevant metal alloys with superior deposit qualities. This work deals with the development of superhard cermet coatings using different types of conventional and fine WC-Co(Cr) powders. The process parameters and the system configuration have been optimised looking for the best coating properties and microstructure. Results are compared in terms of ascertained coating properties (microstructure, microhardness and toughness) and the functional performance under sliding wear.