Three-dimensional numerical simulation of splat formation on substrates in plasma spraying

Plasma sprayed coatings are built up by the accumulation of splats formed by the impacting, spreading and solidifying of molten droplets on the substrate. A three-dimensional computational model including heat transfer and solidification is established to simulate the formation process of a single splat using the computational fluid dynamics (CFD) software, FLUENT. The fluid flow and energy equations are discretized and solved according to typical finite volume method on an unstructured grid. A volume of fluid (VOF) tracking algorithm is used to track the droplet flow with free surface. In order to understand the splat formation mechanism, the process of splat formation caused by impacting and spreading of a molten nickel droplet on a polished mild steel surface is simulated. On this basis, the simulations of impact of a molten droplet on substrate with different conditions including the surface morphology, thermal conductivity, initial temperature of the substrate and the thermal contact resistance are presented. The results clearly show the effect of those parameters on the shape of the final splat and splash behaviors.