NUMERICAL SIMULATION OF THE INJECTION OF SOLUTION SPRAYS INTO A PLASMA JET

Plasma spraying using solution precursors is a relative new thermal spray technology which enables to elaborate finely structured ceramic coatings with nano-and sub-micrometric features. This process involves the injection of a solution spray of ceramic salts into a plasma jet either as a liquid stream or gas atomized droplets. Solution droplets or the stream interacts with the plasma jet and break up into fine droplets. The solvent vaporizes very fast as the droplets travel downstream followed by precipitation and pyrolysis. Depending on the heating and trajectory history of droplets, different states of particles are formed and impact on the substrate to generate coatings. The deposition process and the properties of the coating are extremely sensitive to the process parameters, such as torch operating conditions, injection modes, injection parameters, and substrate temperatures. This paper describes a 3D model to simulate the transport phenomena and the trajectory and heating of the solution spray in a plasma jet. A simplified model is employed to simulate the evolution process and the formation of the solid particle from the solution droplet. The temperature and velocity fields of the jet are predicted. The effect of the injection angle, injection velocity, the torch operating power and the substrate position on the heating and trajectory of injected droplets is discussed. The particle/droplet size distributions on the substrate are predicted for different process parameters.