Plasma spray forming shows overwhelming advantages in rapid fabricating parts and moulds. The coating microstructure is strongly dependent on the splat morphology and inter-splat contact nature. Therefore,it is necessary to investigate the splat formation mechanism in order to analyze the coating properties. A dynamical process of a single fully molten droplet impacting onto a smooth surface was investigated. At the same time,the interaction between the two molten droplets in the horizontal and vertical directions was also simulated. Finally,the simulations of impact of a molten droplet on an inclined plane and a sharp edge were presented. It is concluded that the relative distance of the two droplets strongly influences the dynamics of the two droplets interaction. The various surface conditions have direct effects on the dynamics of splat formation. When a droplet impacts onto an inclined surface and a sharp edge,the splat morphology changes obviously and the phenomenon of break up is observed.
A two-dimensional axisymmetric model,with 8700 and 7500 quadrilateral elements for the fluid and substrate zone separately,was developed to simulate the impacting and flattening process. The volume of fluid technique was employed to track the interface between the air and droplet. The relationships between the droplet pre-impact parameters and the flattening time as well as the flattening ratio were investigated by altering one of the parameters while remaining the others unchanged. The results show that the droplet height reaches its minimum value at approximately half of the spreading time,which also indicates the finish of vertical fluid flow at that time. The flattening ratio increases with the increase of the three pre-impact parameters-droplet diameter,temperature and velocity,even though the flattening time decreases when the droplet velocity increase.
