Thermoelectric magnetohydrodynamic effects on solidification of metallic alloys in the dendritic regime

Abstract

In solidiying metallic alloys, an internal thermoelectric current is present and may influence the solidification structure. On the microscopic scale, this internal current causes Peltier cooling at the tip (heating at the base) of a dendrite, which is a destabilizing effect. On the mesoscopic scale, the thermoelectric current in the presence of an external magnetic field causes fluid motion within the mushy zone, which in turn generates coarseness of the dendritic structure and enhancement of convectice phenomena. Several ways have been used to investigate these thermoelectric magnetohydrodynamic (TEMHD) effects. Experiments realized with binary alloys of different thermoelectric powers demonstrate the relevance of these effects and their influence on the solidification process. Numerical models give first estimates of the typical interdendritic flow velocities due to the TEMHD effects. For the microscopic phenomena, the theoretical analysis shows that the Seebeck and Peltier effects have a destabilizing influence on the liquid-solid interface, even without any external electric or magnetic field. To characterize these phenomena, a new dimensionless parameter Se is introduced, which is a function of the properties of the solidified material.