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

Abstract

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 Co 30 Cr 30 Fe 20 Ni 20 HEA was designed by adjusting composition and prepared by melting. The tensile properties and deformation microstructure evolution were investigated. Co 30 Cr 30 Fe 20 Ni 20 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 Co 30 Cr 30 Fe 20 Ni 20 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). • A metastable as-cast Co 30 Cr 30 Fe 20 Ni 20 HEA was designed by adjusting Co and Cr composition. • Co 30 Cr 30 Fe 20 Ni 20 HEA has large lattice distortion, strong atomic binding force, and low stacking fault energy. • As-cast Co 30 Cr 30 Fe 20 Ni 20 shows excellent strength-ductility synergy at room temperature, including tensile strength of 613 MPa and elongation of 96.2%. • Properties improvement is attributed to high strain hardening rate by utilizing multiple slip interactions of dislocations and twinning-induced plasticity.