Formation mechanisms of self-organized core/shell and core/shell/corona microstructures in liquid droplets of immiscible alloys

Formation mechanisms of self-organized core/shell (CS) and core/shell/corona (CSC) microstructures observed in liquid droplets of immiscible Cu–Fe-based alloys produced by gas atomization processing are investigated with computer simulations. The simulation method is based on a phase field approach that incorporates spinodal decomposition, subsequent coarsening, decomposition-induced fluid flow and Marangoni motion of second-phase droplets immersed in a major liquid-phase matrix. The roles played by each of these processes at different stages during the formation of CS and CSC structures are analyzed systematically as a function of droplet size. Other concurrent mechanisms responsible for the CS and CSC formation, such as coalescence and collisions, and attractive interactions between second-phase droplets, are identified. The differences in volume fraction and surface energies between the Cu-rich and Fe-rich liquid phases are also investigated to ascertain the final morphologies of CS and CSC microstructures. The simulations demonstrate that the influence of the physical process varies (determined by system size) at each stage of the evolution during CS and CSC formation.