Numerical Model of Rapidly Solidified Droplets of Al-33 Wt Pct Cu Eutectic Growth

Rapid solidification of Al-Cu droplets of eutectic composition was carried out using Impulse Atomization (a type of drop tube). Two distinct morphologies were observed: an irregular undulated eutectic assumed to form during recalescence, followed by a regular lamellar eutectic. The volume fraction of each morphology was measured and used to deduce the nucleation undercooling based on the hypercooling limit. A model of the eutectic solidification was developed assuming that the kinetics of the undulated and regular regions is the same and follows scaling laws established experimentally. The simulated solid fraction forming during recalescence matches the experimental undulated eutectic fraction. Furthermore, the heat balance confirms the adiabatic nature of the solidification during recalescence. Good agreement is found between the model and experimental measurements of lamellar spacing for the regular eutectic. However, the predicted spacing of the undulated eutectic is much lower than what is observed experimentally. This difference as well as the nature of this morphology is attributed to coarsening during the remaining of solidification of the very fine eutectic formed during recalescence.