Superior cryogenic strength-ductility synergy in a multiphase lamellar-structured metastable high-entropy alloy

Abstract

Deep space exploration demands materials with exceptional strength and toughness under cryogenic conditions. In this study, we optimize the cryogenic mechanical performance of a metastable Fe₄₆Co₃₀Cr₁₀Mn₅V₅Si₄ (at.%) high-entropy alloy (HEA) through a simple and efficient two-step continuous rolling strategy that combines warm rolling with cold rolling (WRCR). This processing route enhances production efficiency while refining the microstructure into a multiphase lamellar architecture, effectively suppressing deleterious σ phase precipitation. The WRCR-processed alloy exhibits outstanding cryogenic mechanical properties, including a yield strength (YS) of 1.8 GPa, ultimate tensile strength of 2.1 GPa, and a uniform elongation of 16.8% at 77 K. Tailored phase transformation kinetics, driven by high-density dislocations, enable ultrahigh YS while sustaining transformation-induced plasticity (TRIP) effects, thereby enhancing ductility at cryogenic temperatures. Furthermore, the refined lamellar structure promotes crack path deflection and delamination fracture modes, significantly improving fracture resistance. The interplay between movable dislocations and strain hardening governs the yield-point behavior, influencing both the stress drop and the extent of Lüders band deformation. Notably, pre-activated dislocations and martensitic transformation in the WRCR sample effectively suppress Lüders band propagation. This work provides critical insights into the control of heterogeneous deformation and presents a scalable strategy for designing metastable HEAs with superior cryogenic performance.