Morphological instability of cell and dendrite during directional solidification under a high magnetic field

The effects of a high magnetic field on the cellular and dendritic morphology in the Al-Cu alloy during directional solidification have been investigated, and results show that morphological instability of cell and dendrite has occurred. Indeed, at lower growth speeds, a high magnetic field of 10 T caused the cell and dendrite to twist and deflect from the solidification direction. Regular tilted structure forms at moderate growth speeds and the secondary dendritic arm in the upstream direction is more developed than the one in the downstream direction. In the case where the primary trunk has not deflected from the solidification direction, the field has caused the side-branching and the tip-splitting of the cell. These experimental results may be attributed to the thermoelectric magnetic force in the solid cell and dendrite and the change of the surface chemical potential and surface tension of the cellular and dendritic tip. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.