Investigating element segregation and micromechanical heterogeneity in a directionally solidified Co25Fe25Mn20Ni25Ti5 high-entropy alloy

This study fabricated a Co 25 Fe 25 Mn 20 Ni 25 Ti 5 high-entropy alloy (HEA) via directional solidification technique, systematically investigating the formation mechanisms of microscale elemental segregation and micromechanical property heterogeneity under varying solidification rates. These findings reveal that directional solidification preserves the original phase composition of the alloy. Increasing solidification rates promote dendrite refinement, manifested by diminished primary and secondary dendrite arm spacing. Distinct elemental partitioning is observed: Fe and Co preferentially are enriched in primary dendrites and secondary dendrites, while Mn, Ni, and Ti accumulate in inter-secondary dendritic regions. This segregation behavior is primarily attributed to the combined effects of negative mixing enthalpy between components and solute redistribution during non-equilibrium solidification. Micromechanical characterization demonstrates progressive enhancement of local mechanical properties (e.g., nanoindentation hardness) with elevated solidification rates. The observed micromechanical heterogeneity arises from high-melting-point element segregation and lattice distortion, which collectively strengthen the alloy's resistance to plastic deformation at the microstructural level.