Microstructure and Mechanical Properties of FeCoNiCuB_0.1 High‐Entropy Alloy after Casting, Cold‐Rolling Deformation, and Annealing

This study examines microstructural evolution and mechanical properties of FeCoNiCuB 0.1 high‐entropy alloy annealed at 500–1000 °C. The as‐cast alloy exhibits a dendritic FCC matrix with Cu segregation forming interdendritic precipitates and B‐rich bands at grain boundaries. Cold‐rolling produces broken grains, microbands, and deformation twins, dominated by dislocation slip; recrystallization begins above 800 °C. A heterogeneous structure forms at 900 °C, while 1000 °C yields complete recrystallization with annealing twins (grain sizes: 3.9 μm at 900 °C, 8.1 μm at 1000 °C). Mechanically, annealing at 1000 °C increases ultimate tensile strength (560 to 607 MPa) and elongation (15% to 25%). Strain hardening is multistage after 900 °C and 1000 °C annealing, contrasting the monotonically decreasing rate in the as‐cast state. Fracture morphology transitions from mixed‐mode (as‐cast/cold‐rolled) to flatter surfaces with shallow dimples at 900 °C, and finally to fully ductile fracture with deep dimples and reduced cleavage at 1000 °C.