Simultaneously achieved ultra-high crack tolerance and superior strength-ductility synergy in metastable fcc high-entropy alloys containing brittle intermetallic compounds

A novel metastable Fe_48.5Mn₃₀Cr₁₀Si₁₀C_1.5 high-entropy alloy (HEA) was designed by tailoring its dual-phase microstructure—refining equiaxed face-centered cubic (fcc) grains to ∼100 μm and relocating a reduced fraction of brittle β-Mn phase into grain/twin boundaries. This engineered architecture simultaneously elevates yield strength (411 MPa), ultimate tensile strength (840 MPa), and elongation to fracture (45.7 %), effectively overcoming the traditional strength–ductility trade-off. Under tensile loading, the refined fcc matrix activates extensive deformation twinning and progressive deformation-induced fcc → hcp martensitic transformation, generating dense dislocation barriers and volumetric strains that continuously blunt and arrest microcracks within the β-Mn phase. The constrained β-Mn phase, enhanced grain-boundary strengthening, and dynamic TWIP/TRIP hardening sustain a high strain-hardenability and deliver exceptional crack tolerance. This work provides a new strategy for achieving extraordinary strength-ductility synergy and damage tolerance in HEAs.