Hierarchical nano-orderings enable extraordinary cryogenic strength-ductility synergy in a medium-entropy alloy.

Abstract

Cryogenic alloys simultaneously achieving ultrahigh yield strength (YS ≥ 2.0 GPa) alongside substantial uniform elongation (UE) are critically needed, yet fundamentally constrained by the strength-ductility trade-off. Guided by Eshelby's inclusion theory, we reconcile this challenge by designing a novel hierarchical nano-ordering (HNO) architecture within an ultrafine-grained NiCoCr-based multi-principal element alloy, fabricated via combining additive-manufacturing and tailored post-processing. The HNOs-featuring a controlled size distribution and interfacial properties-comprise dispersed incoherent σ-dispersoids (~70 nm), a high density of bimodal coherent L1₂ precipitates (~5 and 26 nm) and widespread, highly-distorted local-chemical-orderings (~0.7 nm). This configuration introduces a stepwise increase in elastic strain energy, which in turn triggers the sequential activation of potent dislocation sources. The resulting mobile dislocations engage in extensive and varied interactions with the nano-orderings during deformation, thereby activating cooperative strain-hardening mechanisms. These nano-architectures thus function simultaneously as dislocation generators, strain-hardening enablers, and strengthening agents. Consequently, this HNO-mediated self-hardening and self-ductilizing mechanisms yield an exceptional cryogenic (77 K) property set: YS of ~1.96 GPa, ultimate tensile strength of ~2.35 GPa, and UE of ~22%, surpassing both the cast counterpart and all previously reported advanced alloys. This strategy establishes a transformative paradigm for designing ultrastrong-yet-ductile materials through integrated manufacturing approaches.