Abstract: A multi-phase heterogeneous FeCoNi-based high-entropy alloy is developed to overcome the trade-off between strength and ductility. By alloying with a small amount of Cu and employing a rapid recrystallization process, it exhibits a good combination of yield strength (roughly 1300 MPa) and ductility (approaching 20 %). Firstly, a multi-phase heterogeneous structure is tailored ranging from nano to micron. Cu is efficiently precipitated as nanoscale clusters (4.2 nm), high-density cuboidal L1₂ particles (20-40 nm) and L2₁ particles (500-800 nm) are found to be embedded in the matrix and a bimodal heterogeneous grain structure (1-40 µm) is constructed. Secondly, the introduction of Cu effectively suppresses the precipitation of coarse L2₁ phase at grain boundaries, reducing its volume fraction by 80 % and replaced by smaller-scale continuous precipitations within the grains. Thirdly, the high mixing enthalpy gap of Cu and the matrix leads to the formation of local chemical fluctuation and the consequential rugged topography in the matrix, which result in retarded dislocation motion and promotes dislocation plugging and interlocking during strain, enhancing yield stress and work hardening rate. This study provides a valuable perspective to enhance strength and ductility via enlarged local chemical fluctuation-tailored multi-phase heterogeneous structures.

Key words: Nanoscale clusters, Local chemical fluctuation, Heterogeneous structures, Dislocation motion, High-entropy alloy