Containerless Solidification Processing and Phase-Field Simulation for Ternary Fe-Cu-Co Peritectic Alloy Under Reduced-Gravity Conditions

We experimentally and theoretically investigated the rapid solidification and microstructural evolution of freely falling droplets of the ternary Fe₄₅Cu₄₀Co₁₅ peritectic alloy, with the critical undercooling temperature of metastable liquid phase-separation initiation being measured to be 38 K. We found that liquid phase separation occurs when the droplet diameter ranges from 80 to 980 μm, resulting in the formation of either microscopically or macroscopically segregated microstructures. The peritectic solidification microstructure was produced when the droplet diameter either exceeded 980 μm or was below 80 μm. The dispersed morphology of the large alloy droplets possessed nonuniformly dispersive characteristics, i.e., proximity to the droplet surface is negatively associated with the size of Cu-rich globules. With the further reduction of the droplet size, the phase-separated morphology first transformed into a core–shell structure and finally displayed a homogeneously dispersed structure. Our theoretical calculations showed that the residual Stokes motion, Marangoni convection, and surface segregation are the dominant dynamic mechanisms for the phase separation and microstructural evolution under reduced-gravity conditions inside the drop tube.