Dynamic evolution process of multilayer core-shell microstructures within containerlessly solidifying Fe(50)Sn(50) immiscible alloy.

Multilayer core-shell structures are frequently formed in polymers and alloys when temperature and concentration fields are well symmetrical spatially. Here we report that two- to five-layer core-shell microstructures were the dominant structural morphology of a binary Fe(50)Sn(50) immiscible alloy solidified under the containerless and microgravity states within a drop tube. Three dimensional phase field simulation reveals that both the uniformly dispersive structure and the multilayer core-shells are the various metastable and transitional states of the liquid phase separation process. Only the two-layer core-shell is the most stable microstructure with the lowest chemical potential. Because of the suppression of Stokes motion, solutal Marangoni migration becomes important to drive the evolution of core-shell structures.