Liquid phase separation and rapid dendritic growth of undercooled ternary Fe₆₀Co₂₀Cu₂₀ alloy

Liquid ternary Fe₆₀Co₂₀Cu₂₀ alloy was undercooled by up to 357 K (0.21 T_L) with glass fluxing method and its rapidly solidified microstructures were investigated by EDS and EBSD technologies. The ternary Fe₆₀Co₂₀Cu₂₀ alloy rapidly solidifies with rapid dendritic growth of the primary γ-Fe phase within 37–243 K undercooling range. When the alloy melt is undercooled to 243 K, an obvious phase separation takes place and the uniform alloy melt separates into (Fe, Co)-rich and Cu-rich phases within 243–357 K undercooling range. The primary γ-Fe phase takes place in a solid-state phase transformation and becomes α-Fe phase in the final microstructure. The microstructure of α-Fe phase transforms from coarse dendrite at small undercoolings to equiaxed grain at large undercoolings. EBSD analysis reveals that the coarse α-Fe dendrites grows anisotropically with a &110 &preferred orientation on condition that undercooling is less than 178 K, whereas no apparent preferred growth orientation is found in the equiaxed grains once undercooling exceeds this critical value. The growth velocity of primary γ-Fe dendrite increases up to 37 ms⁻¹ as undercooling increases to 243 K, but it decreases as undercooling further increases, ascribing to that the dendrite growth is impeded by phase separation.