Packing of sedimenting equiaxed dendrites

International audienceThe packing of free-floating crystal grains during solidification has a strong impact on the phase- change process as well as on the structure and the defects in the solidified material. The packing fraction is affected by the particular dendritic morphology of the grains and by their low inertia re- sulting from the small density difference between solid and liquid. Understanding the grain packing phenomenon during metal alloy solidification is not experimentally possible since packing is coupled to many other phenomena. We therefore investigate the packing of equiaxed dendrites on a model system, consisting of fixed-shape non-convex model particles sedimenting in conditions hydrodynam- ically similar to those encountered in solidifying metals. We perform numerical simulations by a discrete-element (DEM) model and experiments with transparent liquids in a sedimentation column. The combination of experiments and simulations enable us to determine the packing fraction as a function of: (i) the grain morphology, expressed by a shape parameter, and (ii) the hydrodynamic conditions, expressed by the particle Stokes number