Metal alloy solidification in thin capillaries - a study of the solid-liquid interfacial energy anisotropy using a novel approach

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The anisotropy of the interfacial energy of the solid-liquid phase boundary is central with respect to various aspects of metal solidification processes and exerts a crucial influence on the solidified microstructure. The experimental separation of the anisotropy effects from other causes, e.g., morphology changes through melt convection is, however, extremely challenging. Existing methods for the measurement of the anisotropy parameters require considerable experimental effort and lead to substantial scatter of measured values.The present project aims to study the solidification of metallic alloys in thin capillaries with diameters in the order of magnitude of 1µm. Experiments with metal alloys previously documented in the literature did not achieve diameters below 200µm. In the capillaries used in the present project convection effects are suppressed down to the minimum experimental attainable amount which allows the investigation of the shape of the solid-liquid interface quasi free of fluctuations. The interface is crated in a setup for directional solidification with parameters chosen to force morphological instability. By decorating the interface with a secondary phase during quenching its shape remains observable post mortem by scanning electron microscopy. Combining focused ion beam tomography and electron backscatter diffraction, the three dimensional interface shape will be investigated in dependence of its crystallographic growth orientation.Numerical investigations will be conducted using our recently developed "Meshless Front Tracking" (MFT) method for the simulation of phase transformations, which will be extended to the conditions of the solidification in capillaries. In contrast to the established simulation methods, the MFT method is free of any anisotropic influence of the spatial discretization on the simulation results, which renders it especially suited for the examination of anisotropy effects. With this method the influence of both the interfacial energy anisotropy and the crystallographic growth orientation will be numerically investigated. Furthermore, by combining experiments and simulation the anisotropy parameters can be determined. The present project is therefore both a proof of concept for a novel measuring method and a study of the influence of the solid-liquid interfacial energy anisotropy on solidification.