Thermomechanical engineering of nano-twin and dislocation structures for strength-ductility synergy in metastable high-entropy alloys

Abstract

Achieving an excellent strength-ductility synergy remains a central challenge for metastable face-centered cubic (FCC) high-entropy alloys (HEAs). In this study, a thermomechanical processing route consisting of warm rolling followed by annealing was employed to introduce pre-designed defect architectures into two metastable HEAs: a transformation-induced plasticity Cr₂₀Mn₂₀Fe₂₀Co_34.5Ni₅C_0.5 HEA and a transformation- and twinning-induced plasticity Cr₂₀Mn₂₀Fe₂₀Co₃₄Ni₅C₁ HEA. This processing produces unrecrystallized microstructures containing high densities of nano-twins and dislocations, leading to substantial yield strength enhancement while retaining good ductility compared with fully recrystallized counterparts. The C1 HEA achieves a higher yield strength of 1174 MPa with a total elongation of 22.2%, whereas the C0.5 HEA exhibits a lower yield strength of 894 MPa but a higher total elongation of 31.9%. Differences in mechanical response are associated with distinct deformation-induced microstructural evolution during tensile loading. In the C0.5 HEA, a higher fraction of deformation-induced martensite with multiple variants is developed, whereas in the C1 HEA, the transformation is more limited and predominantly involves single-variant martensite, which is associated with lower strain hardenability. These results demonstrate that tailoring defect structures via thermomechanical processing provides an effective pathway for optimizing the strength-ductility synergy in metastable FCC HEAs.