Hierarchical Ordering Induced Ultrahigh Cryogenic Strength and Strain Hardening in a Ni ₂ CoFeV Medium‐Entropy Alloy

ABSTRACT Conventional metallic materials for cryogenic engineering are typically single‐phase face‐centered cubic (fcc) alloys with limited yield strength, whereas ordered phases enhance strength at the expense of ductility, in some cases even causing a ductile‐to‐brittle transition. Here, we overcome this long‐standing limitation by designing a non‐equiatomic fcc Ni ₂ CoFeV medium‐entropy alloy featuring hierarchically ordered, intragranular κ and L1 ₂ intermetallic phases. The resulting tri‐phase alloy achieves a high yield strength of 1.4 GPa at 77 K, enabled by severe lattice distortion from V enrichment together with synergistic strengthening from coherent phase interfaces. Notably, exceptional strain hardening, characterized by an ultrahigh strain hardening rate of ∼7 GPa and a large exponent of 0.85, drives a tensile strength exceeding 2 GPa while retaining a high ductility of 28% at 77 K, surpassing that of most reported fcc‐based high‐/medium‐entropy alloys. The superior cryogenic performance arises from the sequential activation of multiple deformation mechanisms, involving high‐density superlattice dislocations and stacking faults in the coupled fcc/L1 ₂ phases and dislocation multiple slip in the κ phase. This work establishes hierarchical intermetallic ordering as an effective paradigm for cryogenic materials design.