Thermoelectric and magne-tohydrodynamic effects on solidifying alloys

R. Moreau - O. Laskar - M. Tanaka

Laboratoire MADYLAM, Institut National Polytechnique de Grenoble et Centre National de la Recherche Scientifique, 38402 St. Martin d Heres Cedex, France

Abstract
When a solidification front is non-planar, in electrically conducting materials, such as metals or semiconductors, the Seebeck effect generates an electric current (density jTE) at the scale of each non isothermal deformation (dendrite, cell, ...) and Peltier effect causes cooling at its tip (heating at its base). Alone these thermoelectric effects, which are weakly destabilizing, do not significantly modify the solidification process. But, when an external magnetic field B is applied, the Lorentz force jTE´B drives a fluid motion, whose typical velocities may be higher than the speed of the moving front and which may influence the solidification phenomenon. Experiences demonstrate the relevance of such phenomena at all scales (dendrites, freckles, sample). Numerical models have been used in the particular case of vertical directional solidification in the presence of a vertical magnetic field to simulate in details the velocity and concentration fields around a dendrite-like shape. Figs 4, refs 4.