This study investigates the solid particle erosion performance of cold sprayed tungsten carbide-nickel coatings using alumina particles as erodent material. After coating fabrication, specimens were annealed in an electric furnace at a temperature of 600 °C for 1 hour. The coatings were examined in terms of microhardness and microstructure in the as-sprayed (AS) and annealed (AN) conditions. Subsequently, the erosion tests were carried out using a General Full Factorial Design with two control factors and two replicates for each experimental run. The effect of the annealing on the erosion behavior of the coating was investigated at the two levels (AS and AN conditions), along with the impact angle of the erodents at three levels (30°, 60°, 90°). Finally, two regression models that relate the impact angle to the mass loss were separately obtained for the two cold spray coatings.

HVOF spraying process is widely used to improve component life in service due to the high bond strength of the coatings, which is a result of the high particle velocity upon impact, and consequent low coating porosity. However, many parameters can affect metallic coatings properties, especially unmelted particles and oxidation level. Flame parameters, such as calorific power, combustion ratio and temperature, are of prime importance. Moreover, the fuel gas employed in this spraying process can lead to various coating properties and deposition efficiency. The aim of this work was focused on the influence of some fuel gases, namely propane, propylene (LPG) and hydrogen, on stainless steel coating characteristics. A specific domain common for those three gases was determined in order to effectively compare those gases with the same flame parameters. Flame characteristics were computed using a simple model for all the fuel gases considered. Temperature as well as calorific power were fixed. For different substrate temperatures, obtained through a special CO 2 cooling nozzle system, richness was varied from 1.4 to 1.6. Microstructure investigation as well as oxide content and microhardness measurements were conducted. For the same kinetic torch parameters, thickness-per pass gave an idea of the deposition efficiency. In the range studied, deposits properties were quite similar for both LPG fuel gases. Hydrogen led to better characteristics in term of oxide content, although its deposition efficiency was a bit lower. A general law was established to link oxide content within the coatings to the flame parameters. A reasonable regression analysis was obtained for all the coatings sprayed. The combination of cooling efficiency (i.e. CO 2 flow rate) and flame characteristics (i.e. interaction of the particle in flight) led to a good correlation. These correlations were further verified by spraying another metallic powder, namely Inconel 625.

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.

Although high-velocity oxyfuel (HVOF) spray coating is a relatively new thermal spraying process, interest is growing rapidly along with the pace of development in areas such as torch design, powder quality, and modelling. The gases used in HVOF spraying are also important because they directly influence the state of the particle striking the substrate. This presentation reviews the HVOF combustion process with an emphasis on the gases used and their influence on coating quality.