Influence of HVOF spraying parameters on in-flight characteristics of Inconel 718 particles and correlation with the electrochemical behaviour of the coating

The high velocity oxy fuel (HVOF) process is currently used to produce metallic coatings on a wide variety of surfaces, imparting to the base material improved wear, high temperature or electrochemical corrosion resistance. However, HVOF spraying of metals in the atmosphere typically leads to the formation of embedded oxides within a coating. In many service applications, the presence of oxides results in poor coating performance. The gas dynamics of the HVOF spray are particularly important in terms of oxide contents. Therefore, the objective of the present work is to determine the effect of the oxygen/fuel ratio on the particle characteristics during their flight in the jet. A comparison between the oxide contents in Inconel 718 coatings was established as a function of the spray parameters. Electrochemical measurements were performed, giving information on the role of the oxides present in the coating in relation to its corrosion behaviour. Finally, directions are proposed to optimise coating properties obtained with the HVOF process in relation to the in-flight particle characteristics.