Abstract
Cold spray process is an emerging technique that produces high density coatings. Particles are carried by a supersonic gas stream through a De Laval nozzle and, finally, impact on a substrate with high kinetic energy. Low gas temperatures make it possible to maintain sprayed material in solid state during the whole process. Beyond a given velocity, called “particle critical velocity”, particles can bind to the surface and create a coating. This velocity is clearly dependent on both sprayed material and substrate properties. This study deals with the investigation of the influence of the substrate hardness on nickel coating properties. Substrates with different hardness but same chemical composition were used. Samples are then coated with pure nickel or NiCrAlY under the same operating conditions. The measurements of some coating properties and process parameters (deposition efficiency (D.E.), level of porosity, micro hardness) allow the analysis of the effect of substrate hardness on sprayability. It was found that only D.E. is widely influenced by hardness of the substrate. It decreases drastically (especially for NiCrAlY) since hardness of the substrate is higher than hardness of the particle. Porosity level and coating hardness remain constant whatever substrate hardness is.
