Tailoring of dendritic microstructure in solidification processing by crucible vibration

Directional solidification of alloys, which allows the independent control of growth parameters (pulling velocity, temperature gradient), is an experimental method of choice for the investigation of many fundamental problems (e.g. microstructure formation and selection, segregation of chemical species) encountered in the processing of structural materials. Upward directional solidification is carried out on hypoeutectic Al-Ni alloys, under natural and controlled fluid-flow conditions. First, the influence of natural convection on solidified dendritic microstructure is analyzed as a function of growth parameters. Then, directional solidification experiments with axial vibration are performed. It results that crucible vibration can be used to either damp or control fluid flow in the melt, and thus tailor columnar or “equiaxed” dendritic mush. Advanced modeling and numerical simulation are essential to clarify and quantify the various physical effects. Microgravity benchmark experiments under diffusion transport, and possibly with crucible rotation, are foreseen using the Materials Science Laboratory of ESA on ISS.