Harnessing Bifunctional Nitrogen‐Dislocation Interactions for a Record Ultra‐Strong‐and‐Ductile Duplex Titanium Alloy

Abstract Duplex (α+β) Ti alloys often manifest limited uniform elongation (ε u ) mainly originating from the lack of < c + a > dislocations for insufficient work hardening capability and semi‐coherent α/β interfaces for strain incompatibility. The strength–ductility trade‐off of duplex Ti alloys is further amplified by interstitial atoms‐poisoning effects (e.g., N and O). Here, by selecting N atoms with the strongest hardening ability in Ti alloys, a counterintuitive strategy is proposed that harnesses bifunctional N‐dislocation interactions in a model duplex Ti–Cr–Zr–Al alloy to construct a heterogeneous lamella structure, involving the elongated α p grains decorated with N‐rich low‐angle grain boundaries (LAGBs) and densely coherent interstitial‐N α′‐nanotwinned martensites in β‐grains. This structural heterogeneity achieves extremely high yield/tensile strength of ≈1532/1869 MPa in our alloys, which in turn promotes the emission of massive < c + a > dislocations from N‐rich LAGBs and coherent interfaces through stress‐activated bow‐out and cross‐slip processes for relatively large ε u ≈10.2%. This work thus opens an avenue, via bifunctional interstitial atom‐dislocation interactions, to construct a unique microstructure, toward ultrahigh strength and large ductility in interstitial‐strengthening Ti alloys.