A complete mathematical formulation has been developed to numerically solve the fluid dynamics, simultaneous solidification and heat transfer phenomena associated with a droplet impacting a fixed substrate in a typical thermal plasma spray process. The energy equation is solved for both droplet and substrate regions; the solution is based on the enthalpy method for the liquid and solidified parts of the droplet, and the conduction heat transfer in the substrate. The numerical solution for the complete NavierStokes equations is based on the modified SOLA-VOF method using rectangular mesh in axisymmetric geometry. The model permits any desired temperature distributions in the droplet and substrate before the impact, and different thermal boundary conditions at the substrate and droplet free-surface. In particular, the thermal contact resistance at the substrate is permitted. The splat shape, solidification front, velocity distribution, and temperature profile in the entire regions of the splat and substrate are obtained at any desired time elapsed after the impact. The results were obtained for typical DC and RF plasma spray operations through which, the effects of processing parameters and substrate conditions were extensively studied. The predictions were found to be in good agreement with the experimental data reported in the literature; this validated the model and its underlying assumptions.

Keywords