Simulation of the solidification of gas-atomized Sn-5mass%Pb droplets

A simulation method was developed to predict the solidification microstructure of gas-atomized Sn-5mass%Pb droplets. Both internal nucleation caused by a catalyst present in the melt and surface nucleation caused by oxidation are considered. For a given set of atomizing conditions, the model predicts the mode of nucleation, the undercooling, the recalescence time and duration, the post-recalescence plateau duration, the fraction solid at the end of recalescence, and the dendrite growth rate, composition and tip radius during and after recalescence. Predicted droplet microstructures are presented in contour diagrams of dendrite growth rate, composition and tip radius. A separate analysis indicates that dendrite fragmentation is not likely in gas-atomized Sn-5mass%Pb droplets. The developed model provides a scientific basis for improved classification of gas-atomized powders.