Novel insight into evolution mechanism of second liquid-liquid phase separation in metastable immiscible Cu-Fe alloy

Abstract

The metastable immiscible Cu80Fe20 alloys with different diameters were systematically investigated under conventional solidification. Experimental results indicated that the primary and second liquid-liquid phase separation simultaneously occur during solidification. The average size of primary phase-separated Fe-rich spherulites and the interior morphological pattern of minority Cu-rich phase can be greatly influenced by cooling rate due to the dynamic coupling between thermodynamic and kinetic effects. Moreover, various morphological patterns of minority Cu-rich phase in Fe-rich spherulites were observed, which discloses the dynamic evolution process during self-driven second liquid-liquid phase separation. The Marangoni migration, coalescence and coagulation, and Ostwald ripening are the dynamic mechanisms mainly responsible for various morphological patterns of minority Cu-rich phase after phase separation. Such a clear experimental observation of dynamic microstructure evolution for minority Cu-rich phase provides a strong and visualized evidence for the asynchronous crystallization behavior of primary phase-separated Fe-rich spherulites. Phase field simulation was also performed to reveal the dynamic evolution of minority Cu-rich phase during liquid-liquid phase separation. Besides, the experimental Cu80Fe20 alloys exhibit soft ferromagnetic characteristics possessing relatively low coercivity and high saturated magnetization. This present study provides a new strategy to design immiscible alloy with anticipated microstructure possessing tailored properties and desired functionalities.