Verification of a scaling relation for dendritic solidification with interdendritic convection; simulation and experiment. Part I: Simulation

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Alloy solidification under terrestrial conditions is inevitably influenced by buoyancy flow due to high density gradients in the melt caused by segregation. Most available models to predict casting microstructures neglect this effect which significantly affects transport of species and is known to cause detrimental defects like freckles in single crystal solidification. Based on recent phase-field studies in 2D approximation a scaling relation was proposed which predicts the minimum and average spacing of primary dendrites in directional solidification in dependence of the alloy, the process conditions and the vector of gravity. Using today’s computational facilities these predictions shall be verified using 3D simulations. Since it is impossible to quantitatively evaluate the interdendritic flow by experiments, critical experiments which allow an indirect verification of the simulations are planed for a second project period. Phase-field simulation of alloy solidification will be coupled to Lattice-Boltzmann simulation of fluid flow. The simulation will be performed using adaptive multi grid strategies on massive parallel architectures. The project is expected to give a complete picture of the complex mechanisms determining dendritic solidification structures under terrestrial conditions. The scaling theory will pinpoint a route to improved microstructure models to be used in optimization of casting processes.