Modeling the Fluid Flow for Recent Solidification Experiments in Microgravity Electromagnetic Levitation

Abstract

Microgravity electromagnetic levitation provides a unique processing environment for solidification experiments. The contactless processing allows for greater access to the undercooled region of the melt by isolating the sample from its environment and reducing the available heterogeneous nucleation to consistently achieve deep undercoolings. In the ISS-EML, a variety of solidification studies have investigated the relationship between nucleation temperature and flow conditions in metallic melts. These studies include recent work by Kelton et al. in which the coupled flux nucleation model was used to explore solidification in supercooled liquids using glass forming alloys: Vit106, Cu50Zr50, and Ti39.5Zr39.5Ni21. The relationship between fluid flow and nucleation is also a critical factor in recent experiments investigating dynamic nucleation. Unexplained solidification events occurred during both Spacelab Missions IML-2, MSL-1R, and ISS-EML. These experiments encompassed both steady and transient, accelerating flows. Repeatable, anomalous solidification was observed in both flow conditions. The conditions are consistent with dynamic nucleation, which relies heavily on the flow conditions within the sample for nucleation to occur. During these experiments, flow is not directly observable; however, magnetohydrodynamic models allow the flow to be calculated using the properties of the melt and the experimental conditions. These models provide key insights into the flow conditions and the impacts of flow on nucleation in these experiments.