Abstract: Lightweight high-entropy alloys or complex-concentrated alloys have demonstrated great potential for engineering applications due to their high strength and lightweight. However, a weak strain-hardening ability and a limited tensile ductility remain their major hindrance. Here, a multistage strain-hardening effect is developed to ensure a high strength and still a sufficient ductility in a rolled and annealed (Ti₄₄V₂₈Zr₁₄Nb₁₄)_98.5Mo_1.5 (at.%) lightweight refractory complex-concentrated alloy (M1.5A-LRCCA). This multistage strain-hardening behavior is related to the microstructure and the corresponding initial average dislocation density and distribution by comparison with rolled and annealed Ti₄₄V₂₈Zr₁₄Nb₁₄ (M0-LRCCA) and as-cast (Ti₄₄V₂₈Zr₁₄Nb₁₄)_98.5Mo_1.5 (M1.5C-LRCCA). The microstructure, with homogeneously distributed submicron precipitations, a moderate initial average dislocation density, and uniform dislocation distribution (e.g., M1.5A-LRCCA), is susceptible to producing various deformation substructures, such as dislocation substructures (slip bands, Taylor lattices, microbands, DDWs), shear bands, and deformation twins, which results in the multistage strain-hardening behavior. This method of achieving multistage strain hardening behavior through a microstructure modulation is significant for engineering applications of lightweight high-entropy alloys or complex-concentrated alloys, and it might be extended to other lightweight and high-strength alloys.

Key words: High-entropy alloy/complex-contracted alloy, Lightweight, Strain hardening, BCC, Mechanical properties