MICROSEGREGATION MODELING OF MULTIPLE PHASE TRANSFORMATIONS - ATOMIZATION OF AL-NI ALLOYS

A microsegregation model for the solidification of binary alloys is presented. It accounts for diffusion in all phases, and for the nucleation undercoolings and the growth kinetics of the solidifying microstructures forming from the liquid state. The model successively considers the occurrence of several phase transformations taking place in the presence of liquid, including one primary dendritic reaction, one or several peritectic reactions and one eutectic reaction. Volume averaged conservation equations for the mass of solute specie in each phase and at each interface are coupled with a heat balance of the domain assuming a uniform temperature. The diffusion fluxes at the interfaces between phases are calculated through the definition of characteristic microstructural diffusion lengths for which analytical expressions are derived. The model is applied to simulate the solidification of aluminium-nickel droplets produced by atomization. The model predicts the occurrence of a recalescence during the growth of each microstructure, and the progress of peritectic transformations consuming previously formed solid phases, as well as the average composition of each phase.