TIME-RESOLVED IMAGING OF THE MICROSTRUCTURE EVOLUTION DURING DENDRITIC SOLIDIFICATION BY USING SYNCHROTRON RADIATION

摘要

Formation of stray crystals due to fragmentation and development of channel-type segregation in Sn-Bi alloys was observed in-situ by time-resolved X-ray imaging. Sn-13at%Bi alloys were solidified in a mold with a re-entrant channel. Detachment of the fragmented dendrite arms was observed after the planar interface broke down. Fragmentation also occurred after dendrites passing the re-entrant corner grew laterally at rather high growth rates. In both cases, the detachment followed deceleration of the growth rate. In the horizontal solidification of the Sn-Bi alloys, development of the solute-enriched channels was observed in the mushy region. The channels moved toward the solidifying front and incorporated with other channels. Solute transfer in the channels controlled the movement.