Mathematical Modeling and Numerical Simulation of Splat Cooling in Plasma Spray Coatings

Particle deformation and cooling significantly affect the characteristics of thermally sprayed coatings, such as the adhesion and cohesion strength between a splat and a substrate and between splats, as well as the internal stresses of deposits. It is essential to understand these processes for the successful industrial application of thermal spray technology. However, to date, the microstructure of the boundary of a splat and the substrate has not been clarified, although much research has been conducted on splat formation and the cooling process. We have developed a microstructure model of the boundary between the splat and the substrate, based on splat morphology obtained from experiments. In the model, it is assumed that gaps, or voids, and contact areas are arranged on the splat boundary with the substrate in an orderly fashion. The model includes phase changes and heat resistance simulating the function of the microstructure during splat cooling. Assumptions in the model are that ambient gas trapped in the gaps, or voids, transfers heat only by conduction and not by convection or radiation. The results of the simulation indicated that the extent of gaps, or voids, significantly affects the rate of decrease of the average temperature of the splat surface, as well as the temperature distribution inside the splat.