Observations and simulations for phase separation process of immiscible Fe50Sn50 alloy droplets placed on a chilling surface

Liquid phase separation and microstructure evolution mechanisms of immiscible Fe50Sn50 alloy droplets placed on a chilling surface have been investigated by both arc melting experiments and lattice-Boltzmann simulations. The pattern selection of phase-separated morphologies strongly depended on the sample diameter. With the reduction in sample size, phase separation time was shortened, two-layer macro -segregation morphologies first transformed into intermediate phase-separated morphologies and finally changed into a homogeneously dispersed microstructure. The farther away from the sample bottom the longer the phase separation time and the larger the Sn-rich phase. A heat transfer equation was proposed to analyze the temperature field characteristics of Fe50Sn50 alloy droplets placed on the surface of a water-cooled copper mold. Theoretical analyses revealed that the sample gradually cooled from the bottom to the top of the sample. There existed a relatively high temperature gradient of several hundred Kelvins per millimeter between the top and the bottom of the arc melted sample, which induced the occurrence of an extremely intense Marangoni convection. The smaller the sample size the larger the temperature gradient and the greater deviation-degree of Fe-rich zone in two-layer macrosegregation structure from the bottom of the sample. The simulated two-layer phase-separated morphology agreed well with the experimental observations. Numerical simulations demonstrated that the effect of Marangoni convection on the phase separation was significantly stronger than the Stokes motion, and Fe-rich globules with a larger density tended to move upward to form a Fe-rich zone deviating from the bottom of the sample.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

The liquid phase separation and microstructure evolution mechanisms of immiscible Fe50Sn50 alloy droplets on a cooling surface were studied using arc melting experiments and lattice-Boltzmann simulations. The selection of phase-separated morphologies was strongly influenced by the sample diameter. As the sample size decreased, the phase separation time shortened and the two-layer macro-segregation morphologies transformed into intermediate phase-separated morphologies before finally becoming homogeneously distributed microstructures. A heat transfer equation was used to analyze the temperature field characteristics of the droplets on a water-cooled copper mold, revealing that the sample cooled gradually from bottom to top. The effect of Marangoni convection on phase separation was found to be stronger than Stokes motion, with Fe-rich globules tending to move upward and deviate from the bottom of the sample in a larger density region.