Influence of a high magnetic field on columnar dendrite growth during directional solidification

The influence of a high magnetic field on the growth of MnBi, alpha-Al and Al3Ni dendrites in directionally solidified Bi-Mn, Al-Cu and Al-Ni alloys have been investigated. Results indicate that the magnetic field changes the dendrite growth significantly. Indeed, the magnetic field aligns the primary dendrite arm and the effect is different for different dendrites. For the MnBi dendrite, an axial high magnetic field enhanced the growth of the primary dendrite arm along the solidification direction; however, for the alpha-Al and Al3Ni dendrites, the magnetic field caused the primary dendrite arm to deviate from the solidification direction. At a lower growth speed, a high magnetic field is capable of causing the occurrence of the columnar-to-equiaxed transition (CET). Moreover, it has also been observed that a high magnetic field affects the growth of the high-order (i.e., secondary and tertiary) dendrite arms of the alpha-Al dendrite at a higher growth speed; as a consequence, the field enhances the branching of the dendrite and the formation of the (111)-twin planes. The above results may be attributed to the alignment of the primary dendrite arm under a high magnetic field and the effect of a high magnetic field on crystalline anisotropy during directional solidification. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.