DIRECTIONAL SOLIDIFICATION EXPERIMENTS IN MATERIALS SCIENCE LABORATORY OF THE INTERNATIONAL SPACE STATION

Solidification is taking place in industrial applications ranging from casting, welding, soldering to additive manufacturing. Even for materials that are shaped by plastic deformation or machining, the ingot or workpiece is generally produced by casting. Although application of these processes may modify solidification microstructure, the initial cast structure still plays a deterministic role in chemical and morphological distribution in the material. Material properties are highly dependent on these distributions as well as the microstructural features of the material. Therefore, investigating microstructure evolution during solidification is crucial. On Earth, due to convection in the liquid during solidification of alloys, 2D samples, i.e. thicknesses on the order of µm, must be used to avoid convection and obtain quantitative results. However, the wall thickness of cast components used in industry are at least mm-thick. In order to understand the fundamentals of the solidification process in 3D samples, and examine the direct effect of experimental parameters on microstructure selection, experiments were performed in microgravity conditions. Details of these microgravity experiments performed in the International Space Station as well as the ones performed on Earth in the Microstructure Evolution Laboratory are given in this article. Additionally, objectives of both µg and 1g experiments are summarized