Nano-twinning induced high strain hardening behavior in a metastable as-cast Co₃₀Cr₃₀Fe₂₀Ni₂₀ high entropy alloy at room temperature

High entropy alloys (HEAs) utilize multiple deformation mechanisms to overcome the strength-ductility trade-off by deformation treatment and low temperature conditions. To develop original engineering materials with strength-ductility synergy properties, we induced multiple deformation strengthening mechanisms into the as-cast face-centered cubic (FCC) HEAs at room temperature. A metastable as-cast Co₃₀Cr₃₀Fe₂₀Ni₂₀ HEA was designed by adjusting composition and prepared by melting. The tensile properties and deformation microstructure evolution were investigated. Co₃₀Cr₃₀Fe₂₀Ni₂₀ HEA has larger lattice distortion, stronger atomic binding force, and lower stacking fault energy (SFE) than equiatomic CoCrFeNi HEA. The low SFE and large grain size promote multiple slip systems (single slip, crossing slip, and blocked slip) activation and the formation of deformation twins. The as-cast Co₃₀Cr₃₀Fe₂₀Ni₂₀ shows excellent properties at room temperature, including yield strength of 267 MPa, tensile strength of 613 MPa, and fracture strain of 96.2%, which increases by 92.2%, 47.9%, and 10.50% than that of equiatomic CoCrFeNi HEA. The enhancement of yield strength results from solid solution strengthening and strong atomic binding forces. The tensile strength-ductility synergy is attributed to a high strain hardening rate by utilizing multiple slip interactions of dislocations and twinning-induced plasticity (TWIP).