A gas shroud nozzle for HVOF spray deposition

Properties of MCrAlY coatings obtained by High Velocity Oxy-Fuel (HVOF) thermal spray process operated in a standard configuration were compared with those obtained using a gas shroud attachment to the HVOF gun. Our measurements show that the attached gas (nitrogen) shroud nozzle considerably reduces the oxygen content in the coating without an appreciable change in the microstructure. The particle temperatures were decreased by an average of 100 C at a standoff distance of 0.275 m (11 inches). There was also a large reduction in the particle velocity at this distance. Both these effects were related to the excessive amount of nitrogen used for shroud.ing.