Controlling Freckle Defect Formation using Magnetic Fields

The application of a static magnetic field has been shown to have a significant effect on channel formation in the GaIn freckle defect forming alloy. The underlying mechanisms are via Thermoelectric Magnetoydrodynamics (TEMHD) driving inter-dendritic fluid flow. Thermoelectric currents form due to the inherent thermal gradient and spatial variation in composition due to solute partitioning. In the presence of a magnetic field these currents interact generating the flow driving Lorentz force. Convective solute transport then alters solidification behaviour. This causes spatial repositioning of the channel, preferential growth, secondary effects such as plume migration and complex grain boundary interactions.
TESA (ThermoElectric Solidification Algorithm) is a parallel Cellular Automata Lattice Boltzmann based numerical model that has been validated against Xray synchrotron experiments. Using TESA the dependency of the magnetic field orientation and magnitude has been explored, providing further predictions for controlling the channel.