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 microst ructures are mainly characterized by alpha-Cu dendrites plus zeta phase whi ch forms in the interdendritic areas within the whole undercooling regime. With the increase of undercooling, both the secondary arm spacing of primar y alpha-Cu dendrite and the layer thickness of the peritectic zeta phase de crease. The primary trunk and secondary arm of alpha-Cu dendrites show roun d shape under small undercooling condition, whereas they keep a good dendri tic shape within a large undercooling regime. indicating that the peritecti c reaction proceeds for a relatively longer period of time in the former ca se. The volume fraction of peritectic zeta phase increases with undercoolin g, but that of alpha-Cu dendrite shows a decreasing tendency. Furthermore, drop tube experiments were also performed to reveal the competitive nucleat ion and growth mechanisms of primary alpha-Cu dendrite and peritectic phase zeta. Calculations based on the current dendritic growth model are made to analyze the crystal growth kinetics during the rapid solidification of und ercooled Cu-Ge peritectic alloy. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.