Formation mechanism of layered microstructure and monotectic cell within rapidly solidified Fe_62.1Sn_27.9Si₁₀ alloy

Ternary Fe_62.1Sn_27.9Si₁₀ monotectic alloy is rapidly solidified in drop tube with the freely-falling-body techniqual and with melt spinning method separately. The phase separation, the microstructure characteristics, and the heat transfer of this alloy are investigated theoretically. Under free fall condition, the core-shell structure with two layers is formed because of Marangoni migration and surface segregation, where the Sn-rich phase is always located at droplet surface and the Fe-rich phase in the center. With the decrease of droplet diameter, both cooling rate and temperature gradient increase quickly, which facilitates the rapid growth of monotectic cell. With the increase of wheel speed, the cooling rate of alloy ribbon increases from 1.1×10⁷ to 6.5×10⁷ K/s, the fluid flow and the phase separation are suppressed to a great extent, and the "nine layers → two layers → no layer" structural transition occurs during the rapid solidification of Fe_62.1Sn_27.9Si₁₀ alloy obtained by the melt spinning method. Meanwhile, the FeSn+L₂→FeSn₂ peritectic transformation is also suppressed, thus resulting in different phase constitutions as compared with the case of free fall condition. The energy dispersive spectroscopy (EDS) analysis reveals that the αFe phase exhibits a conspicuous solute trapping effect during rapid solidification.