Study of ternary eutectic microstructures using 3D phase-field simulations and directional solidification experiments of Al-Ag-Cu

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The microstructure evolution of three-phase eutectics in 3D contains a broad variety of morphologies and is by no means understood, especially not the conditions for the occurrence of the various regular and irregular structures. The aim is to achieve substantial progress in understanding the microstructure formation in Al-Ag-Cu by a suitable combination of 3D phase-field modeling and dedicated experiments for a selected range of velocity jumps and compositions. A particular focus of the collaborative project is a mutual development of an integrated postprocessing framework to characterize simulated and experimental 3D microstructures by implementing appropriate programming interfaces and by applying identical tools. On the basis of the joint framework, the simulation results will be compared with experimental photographs and measured structural quantities.The team at KIT will employ a new quantitative phase-field model and performance improved simulation method developed in the first funding period to get insight into 3D microstructure formation such as brick structures, two phase rods, spirals and coupled growth. A thermodynamical data set of Al-Ag-Cu is incorporated in the phase-field model. In coordination with the experiments in Cologne, we aim to systematically vary the imposed pulling velocity jumps and alloy composition and analyze the resulting concentration profiles and microstructural properties such as morphology type, phase fraction, spacing and surface area. Based on the parallel nature of the code, 3D simulation studies will be carried out on high performance clusters and enable to derive morphology transition diagrams and correlation functions between the microstructure characteristics and solidification conditions. A particular focus will be the investigation of the effect of solid-solid anisotropy on the pattern formation and morphological pathways.The team at DLR will perform directional solidification experiments using the so-called ARTEMIS facilities, aerogel based furnaces which, due to the utilization of silica-aerogels, control a flat solid-liquid interface, the solidification velocity and the temperature gradient ahead of the interface over the processing length. The experiments will be performed in a velocity range of 0.1 mu m/s to 5 mu m/s with a temperature gradient of 3 K/mm. The microstructure evolution will be analyzed with newly developed methods such as nearest neighbor (NN) probabilities, NN distances for the different phases, average phase particle areas, and particle number densities. Besides light microscopy, we will use SEM with EDX and EBSD for local and global composition variations, determination of phase compositions, and local orientation of the phases. Some of the samples will be analyzed in 3D using x-ray tomography as established in the first period. We plan to apply external measurement capabilities like those at BESSY, DESY and ESRF.