Synergistic improvement of strength and ductility in dual-phase Fe67(CoCrNiMn)33 high-entropy alloy via heterostructure design

This study addresses the challenges of low strength and susceptibility to ductility degradation in face-centered cubic (FCC) high-entropy alloys (HEAs). Using the dual-phase Fe 67 (CoCrNiMn) 33 HEA as a model, we introduced a heterogeneous microstructure via cold rolling followed by short-time annealing to explore the synergistic optimization of strength and ductility. It demonstrates that annealing at 640 °C yields the most favorable combination of mechanical properties, with a tensile strength of 770 MPa and a uniform elongation of 25.4 %. It reveals that approximately 50 % of the cold-deformed structure is preserved after annealing, creating a hard-soft phase hetero-interface that facilitates coordinated strain distribution. The deformation process is further enhanced by the interaction of stacking faults, twinning, and the TRIP effect (FCC→HCP→BCC phase transformation), which collectively improve plasticity. Simultaneously, the presence of Lomer-Cottrell locks contributes to strengthening the material. The alloy retains its dual-phase FCC+BCC structure throughout the treatment, underscoring the effectiveness of the heterogeneous microstructure and the multi-mechanism synergy in optimizing the mechanical properties of the HEA.