Microstructure evolution of undercooled iron-copper hypoperitectic alloy

Fe(50)Cn(50) hypoperitectic alloy has been undercooled and rapidly solidifi ed by glass fluxing technique and drop tube processing. It is found that in both procedures metastable phase separation occurs if this alloy melt is u ndercooled to a certain extent. In the glass fluxing experiment, the obtain ed maximum undercooling is 81 K, and the sample is macroscopically separate d into one upper Fe-rich part and one lower Cu-rich part. These two parts s ubsequently exhibit secondary phase separation, which is characterized by C u-rich blocks precipitated in the Fe-rich part and Fe-rich spheres disperse d in the Cu-rich part. During drop tube processing, a 'dendritic-partially separated-entirely separated-mixed structure' microstructural evolution tak es place in the rapidly solidified particles. Macroscopic phase separation appears as the central Fe-rich part and surrounding Cu-rich part, while sec ondary phase separation is characterized by Cu-rich spheres distributed in the Fe-rich part and Fe-rich spheres scattered in the Cu-rich part. The pri mary gamma -Fe dendrite growth is mainly controlled by solute diffusion and conspicuous solute trapping has taken place. As for the coalescence of sep arated Fe-rich droplets, the Stokes motion is dominant in glass fluxing exp eriment, whereas in drop tube it is weakened and the effect of Marangoni mi gration becomes evident. (C) 2001 Elsevier Science B.V. All rights reserved .