Microscopic and thermodynamic insights into Ti-enriched high-entropy intermetallic formation during solidification of a multicomponent alloy.

The effect of Ti addition on solidification and intermetallic phase formation in the FeMn40Co10Cr10C0.5 HEA was investigated by combining advanced microscopy with CALPHAD thermodynamic calculations. The Ti-free FeMn40Co10Cr10C0.5 alloy solidified predominantly as an FCC dendritic structure with limited elemental partitioning. In contrast, the addition of 2 at% Ti produced a multiphase microstructure comprising 78.4 vol% FCC matrix, 20.3 vol% Ti-enriched intermetallic phase, and 1.3 vol% TiC, with a mean TiC particle size of ∼0.89 μm. Elemental mapping and line-scan analyses showed relatively uniform distributions of Fe, Mn, Co, and Cr within the FCC matrix, localized Ti enrichment within the interdendritic constituent, and pronounced Ti and C enrichment in discrete carbide particles. The Ti-enriched phase formed an interconnected network along the interdendritic channels. Thermodynamic calculations indicated that this phase becomes stable near the terminal stage of solidification. The results demonstrate that the Ti-enriched intermetallic phase nucleates from the compositionally enriched residual liquid through the combined influence of solidification-induced microsegregation, negative mixing enthalpies between Ti and the transition-metal constituents, and Ti-induced atomic-size mismatch, while TiC precipitates from the remaining liquid.