| Abstract: | Directional solidification was performed in Cu 30Ni alloy melt undercooled in the range 105-155 K, and the structure was investigated. The results indicated that the dendrite arm spacings are first dependent on undercooling prior to nucleation. As undercooling increases, the thickness of thermal diffusion field and solute diffusion field decreases due to the ascent of dendrite growth velocity, and the dendrite remelting occurring in solidification abates. So primary and secondary arm spacing all decrease. At the undercoolings higher than 150 K, however, secondary arms degenerate because of the further closing of the primary branches, and enlarge their spacing. The dendrite arm spacings are also related to the position in specimens. At the two ends of specimens, especially the initial end of solidification, the favorable heat dissipation condition leads to smaller spacings. Primary as well as secondary arm spacings always reach their maximum at the central part of the specimens where the local solidification time is the longest. |
