Owing to high particle velocity upon impact, and consequently low porosity and high bond strength of so-obtained coatings, HVOF spraying process is widely used to improve components life in service. However, many parameters can affect metallic coatings properties, especially un-melted particles and oxidation level. Flame parameters, such as calorific power, combustion ratio and temperature, are of prime importance. The aim of this work was focused on the influence of these parameters on stainless steel coatings characteristics. For different substrate temperatures, maintained through CO2 cooling nozzles, those parameters varied independently. Flame characteristics were computed using a simple model for propylene as fuel gas. Microstructure investigation as well as oxide content measurements and microhardness were obtained. It appeared that combustion temperature, in the range studied (2600-2750K) was not a critical factor. However, combustion ratio and calorific power greatly influenced coating properties: an increase of oxide content, and consequently a higher microhardness, was observed when combustion ratio decreased as well as when calorific power increased.

Among the different wires used in arc spraying, copper is a material of choice in some applications. Its malleability is used to allow an easy machining procedure after spraying. This article focuses on the limitations of the oxidation of copper during arc spraying and its influence on coating process and properties. The aim of this series of experiments was to improve coating properties of copper sprayed with the electrical wire arc spraying process by substituting compressed air with nitrogen. These experiments show that coating properties, as well as electric wire arc spraying process, are strongly influenced by the gas employed as the atomising element.