Solidification microstructure evolution and its corresponding mechanism of metastable immiscible Cu80Fe20 alloy with different cooling conditions

Undercooling greatly influences the resultant solidification microstructure of an alloy, especially for metastable immiscible Cu-Fe alloy. In the present paper, solidification microstructure evolution of metastable immiscible Cu80Fe20 alloy was studied under different cooling conditions. For the first time, it is found that the liquid-liquid phase separation in Cu-Fe alloy is triggered by constitutional undercooling ahead of the solid-liquid interface. When the cooling rate is about 50-100 K/s, the liquid-solid transformation primarily takes place, and the liquid-liquid phase separation only exists in a small region or the interdendritic region about several tens to hundreds of microns. The liquid-liquid phase separation is ascribed to the large constitutional undercooling according to the calculation and occurs behind the liquid-solid transformation, which is different than found in previous studies. However, only normal liquid-solid transformation occurs and the morphology of the Fe-rich phase remarkably changes from cellular to developed dendrites in a cooling rate range of 350-560 K/s. The results provide significant guidance for industrial preparation and a necessary consideration for the study of metastable immiscible Cu-Fe alloy.