In-Situ Observation of Flow of Residual Liquid Deducing from the Movement of Bubbles Generated at the End of Solidification

Abstract

In-situ observation of flow of residual liquid has been deduced from the movement of bubbles generated at the end of solidification. Succinonitrile-water alloy system was used for experiment. At the final stage of solidification, some bubbles formed at the interdendritic region, because of the limit of solubility of air in the liquid phase. These bubbles grew and traveled as the solidification proceeded, keeping the position where the fraction solid was approximately constant. The loci of some bubbles were characterized, changing the solidified structure from columnar to equiaxed. In case of columnar dendrites, the bubbles moved along and normal to the primary trunks. On the other hand, in case of fine equiaxed grains, the loci of bubbles were very smooth. In case of coarse equiaxed grains, the loci of bubbles were very complex. Since the bubbles could not penetrate the equiaxed grains, they went around the equiaxed grains along the boundary. Therefore, the path was circuitous and complex. These observations suggested that the complex shape of solidified structure may increase the resistance of liquid flow at the final stage of solidification.