Structurally Complex Precipitates Enhance Strength-Ductility Synergy in a Duplex Medium Entropy Alloy

Chemically homogeneous intermetallic nanoprecipitates (INPs), despite their high strength, are intrinsically hard and brittle and often suffer from glide-plane softening, which can strengthen alloys but severely degrade uniform elongation. This strength–ductility trade-off is further exacerbated at cryogenic temperatures by the inherent brittleness of bcc-based phases in precipitate-strengthened fcc/bcc duplex alloys. Here we propose a strategy that overcomes these limitations through the design of structurally complex INPs, i.e., the ductile B2 multicomponent INPs (MINPs) assembled with dispersive nanocores and a chemical-heterogeneity shell, in duplex fcc/bcc Fe₅₈Ni₁₆Cr₁₆Al₁₀ (at%) medium-entropy alloys (Fe-MEAs). Within the bcc constituent, these coherent core–shell B2 MINPs serve the dual role of dislocation sources and obstacles, analogous to the ordinary incoherent B2 MINPs that trigger twinning-induced plasticity in the fcc constituent, yet they are substantially more effective in load transfer for high yield strength and in self-hardening for large uniform elongation. Critically, the core–shell nanostructure suppresses the glide-plane softening typical of conventional INPs and promotes the activation of unusual ⟨111⟩ dislocation multiplication and interactions under cryogenic conditions. This work demonstrates a structural complexification strategy for designing self-hardening MINPs, opening a pathway to ductile, high-strength materials for advanced cryogenic structural applications.