5th International Conference on Advances in Solidification Processes (ICASP-5) 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5)

Directionally solidified binary eutectics are of great practical interest as self-organized composite materials with tunable microstructural features. In a first approach, eutectic microstructures can be classified into rod-like and lamellar ones. Their formation dynamics, which results from a complex diffusion controlled dynamics of coupled-growth front patterns, has been extensively studied by in situ experimentation and time-resolved numerical simulations. Important results have thus been obtained on the morphological stability of eutectic growth shapes and some pattern selection processes. However, the problem of the possible coexistence of rod-like, lamellar, and other more complex shapes in a given sample, in brief, the lamellar-to-rod transition, still remains poorly explored. We have developed an in-situ experiment method that permits to visualize optically the evolution of coupled-growth front patterns in real time in transparent eutectic alloys. In the succinonitrile-(D)camphor system, we identified and located the stability limits (rod elimination, and rod splitting, respectively) of the stability interval of hexagonal eutectic-rod patterns. In this system, we also discovered a transition from rods to lamellae in the presence of a finite-size effect in semi-thin samples. These conclusions could be drawn from laboratory experiments during which thermosolutal convection in the liquid was negligible. On ground, this narrows the range of explorable parameters (composition, thermal field) and prevents one to undertake a systematic study of the lamellar-to-rod transition in large samples. We undertook a science-in-microgravity project (ESA/NASA) called TRANSPARENT ALLOYS (TA). An apparatus for in situ directional solidification experiments in large samples has been installed on board the ISS/MSG (Dec. 2017). We will present the results of the first TA campaign (January-March 2018 ; SEBA program) in collaboration with U. Hecht and V. Witusiewicz (Access e.V., Aachen, Germany).