2012 Volume 76 Issue 4 Pages 240-245
In order to investigate the mechanism for equalization of primary dendrite arm spacing, in-situ observation of solutal field using succinonitrile-H2O-dye system has been carried out. The brightness, which corresponds to the concentration of dye, has been characterized by an image analyzer along the centerline of interdendritic region. When the local primary dendrite spacings were uneven, the brightness along the centerline of interdendritic region was low in case of local primary dendrite arm spacing was large. After growth with rather long distance, the local primary dendrite arm spacings became even and the brightness along the centerline of interdendritic region became uniform. The solutal profile along the interdendritic region qualitatively agreed with the calculation results of newly developed model. A dendrite trunk is prone to grow toward the wide-spacing-region because the solute concentration of this side is lower than that of the other side. This leads to equal primary spacing.
