Experimental Explorations and Lattice-Boltzmann Simulations for Macrosegregation Evolution Kinetics of Glass-Fluxed Immiscible Alloys

Immiscible alloys usually display various macrosegregation patterns induced by liquid phase separation. Here, the macrosegregation evolution kinetics for a model Fe65Cu35 immiscible alloy were systematically investigated by both glass fluxing experiments and lattice Boltzmann simulations. The glass-fluxed Fe65Cu35 melt was undercooled between 24 K and 291 K (0.17 TL). For an undercooling lower than 121 K, the sample shows a relatively homogeneous macrostructure without phase separation. With increasing undercooling above 189 K, metastable liquid phase separation occurs, which leads to the formation of two typical macrosegregation patterns. Meanwhile, both the phase separation undercooling and the phase separation time are linearly increased. In the undercooling range of 189 K to 248 K, the phase-separated morphology is mainly characterized by an eccentric three-layer core–shell structure consisting of a Cu-rich shell, an Fe-rich layer and a Cu-rich core eccentric towards the ground. As the undercooling temperature exceeds 248 K, a two-layer core–shell macrosegregation composed of an Fe-rich core and a crescent-like Cu-rich shell eccentric towards the ground is frequently preserved. A two-dimensional lattice Boltzmann model, which simultaneously considers the combined effects of Marangoni convection, surface segregation and the gravity field, is proposed to sufficiently clarify the evolution kinetics for typical macrosegregation patterns. Numerical simulations demonstrate that Marangoni convection, surface segregation and Stokes motion are dominant dynamic mechanisms responsible for the macrosegregation evolution under glass fluxing conditions. Furthermore, the temperature gradient at the time of occurrence of metastable phase separation together with the phase separation time is found to play a crucial role in the selection of the macrosegregation pattern.