Influence of process variables on the qualities of detonation gun sprayed WC–Co coatings

Detonation gun (D-gun) spraying is one of the most promising thermal spray technology for high quality wear resistant coatings. Of all the ceramic materials that can be D-gun-sprayed, WC is the most widely established and these coatings have already gained industrial acceptance for diverse applications. The use of D-gun-sprayed WC–Co coating as protection against aggressive environment requires a precise knowledge of the influence of spraying process parameters on the coating characteristics and properties (porosity, adherence, roughness, hardness, etc.). In this article, experimental results are presented in terms of the structure, including surface roughness, XRD patterns and porosity, as well as adhesion strength, hardness, and fracture toughness of D-gun-sprayed WC–Co coatings as a function of spraying distance from nozzle exit to substrate and ratio of O2:C2H2. It is found that both the spraying parameters influence structure and properties of D-gun-sprayed WC–Co coatings. The decarburization of WC–Co powders during the spraying is little even when the highest oxygen–fuel ratio was employed. When the higher oxygen–fuel ratio was employed, hardness and adhesion increase, while, porosity and fracture toughness decrease, which can be attributed to the higher temperature and velocity feed powders obtained from the detonation wave. On the other hand, denser microstructure, higher adhesion strength and higher hardness appear when the coating was deposited at spraying distance of 110–20 mm, while fracture toughness is a little lower, which may come from the best compromise of decreasing velocity and lagging of heat transfer process for the particles to obtain a good molten state.