Analysis of solidification in the spray atomization process

Spray atomization is a process for the production of net or near net shape products. In this process, a molten stream of metal is disintegrated into a fine dispersion of droplets by high velocity gas jets. The resulting semisolidified droplets are directed towards a substrate where they impact and collect as rapidly solidified splats. High rates of solidification are achieved as a result of the thinness of the splats and the rapid heat extraction during fight in the inert atmosphere. In this paper, a mathematical formulation for spray atomization, based on classical nucleation and growth theory and kinetics, is presented. The model deals with the following: the production of metallic droplets by high pressure inert gas atomization, including the droplet-gas interaction and the resulting droplet size distribution; the expected mode of nucleation of the solid phase, correlated to the droplet size; the thermal and solidification histories of the droplets in flight. The influence of the process parameters, such as the atomization gas pressure, the wetting angle, the geometrical features of the atomizer and feeding crucible, the distance between the atomization nozzles and the substrate, on the final microstructure is evaluated. As a result of this analysis, the optimal choice of the process parameters can be made, for the production of the desired microstructure.