Rapid solidification of undercooled Cu-Ge peritectic alloy

Bulk samples of Cu-14.4 wt% Ge peritectic alloy has been undercooled by up to 200 K (0.166 T_L) with a glass fluxing technique. The solidified microstructures are mainly characterized by α-Cu dendrites plus ζ phase which forms in the interdendritic areas within the whole undercooling regime. With the increase of undercooling, both the secondary arm spacing of primary α-Cu dendrite and the layer thickness of the peritectic ζ phase decrease. The primary trunk and secondary arm of α-Cu dendrites show round shape under small undercooling condition, whereas they keep a good dendritic shape within a large undercooling regime, indicating that the peritectic reaction proceeds for a relatively longer period of time in the former case. The volume of peritectic ζ phase increases with undercooling, but that of α-Cu dendrite shows a decreasing tendency. Furthermore, drop tube experiments were also performed to reveal the competitive nucleation and growth mechanisms of primary α-Cu dendrite and peritectic phase ζ. Calculations based on the current dendritic growth model are made to analyze the crystal growth kinetics during the rapid solidification of undercooled Cu-Ge peritectic alloy.