In metals and alloys, solute segregation at grain boundaries typically undermines cohesion and ductility. Here, we overturn this paradigm by showing that solvent Fe atoms can preferentially enrich low-angle grain boundaries (LAGBs) in a ferrous alloy, dramatically enhancing ductility. Cold rolling and aging generate coherent nanoprecipitates, a high dislocation density, and abundant LAGBs in an austenitic matrix, yielding an ultrahigh tensile yield strength of ∼ 1.74 GPa. Moreover, the solvent Fe enrichment at LAGBs lowers local stacking fault energy and activates austenite-to-martensite transformation under load. This transformation-induced plasticity effect stabilizes plastic flow, enabling a uniform elongation of ∼ 26.2 % despite the alloy’s exceptional strength. Our findings challenge conventional views of segregation and offer a new design strategy for ultra-strong, highly ductile alloys.

Ultrahigh-strength bulk alloys with martensitic structures are essential for heavy-duty applications and infrastructure. However, they often contain small-angle grain boundaries (SAGBs), which enhance ductility but weaken resistance to dislocation motion. This limitation restricts tensile strength to below 2.5 GPa, even when nanoprecipitates or hierarchical architectures are introduced. Here we overcome this limitation by developing a near-single-phase martensitic alloy with a tensile strength exceeding 3 GPa. In the model (Fe₄₉Co₄₀Mo₁₁)_99.6B_0.3C_0.1 (at.%) alloy, cold rolling followed by low-temperature annealing introduces a high density of dislocations and drives Mo, C and B atoms to cosegregate at the SAGBs, forming interface complexes. These complexes stabilize the SAGBs, reinforce barriers to dislocation motion and still permit dislocation transmission across boundaries. As a result, the alloy achieves a tensile yield strength of 3.05 GPa and a fracture elongation of 5.13%, setting a benchmark for ultrahigh-strength, ductile alloys. This simple, scalable process integrates seamlessly with existing manufacturing methods and opens a path to next-generation structural materials.

Coherent precipitation-hardened alloys often struggle to achieve both ultrahigh strength and exceptional ductility due to their limited resistance to dislocation motion and vulnerability to glide plane softening. Here, we tackle these challenges by introducing multicomponent precipitates with much increased antiphase boundary (APB) energy. In a model Ni₃Al-type (L1₂) precipitation-hardened face-centered cubic (FCC) NiCo-based alloy, we incorporate multiple elements at the Al sublattice sites within the precipitates, reducing antisite defects and enhancing ordering degree. This process yields multicomponent precipitates with an ultrahigh APB energy (~308 ± 14 millijoules per square meter), which notably strengthens the alloy. Moreover, the exceptionally high APB energy transforms the deformation mechanism from dislocation shearing to stacking fault shearing, thereby avoiding glide plane softening. These result in a tensile yield strength of 1616 ± 9 megapascals, an ultimate tensile strength of 2155 ± 22 megapascals, and a uniform elongation of 10.1 ± 0.3% for the alloy.

NiTi-based composites possess great potential for concurrently improving both mechanical and functional properties. However, relying on traditional alloy design principles limits the design space and greatly hinders the advancement of high-performance NiTi-based composites. The concept of high-entropy alloys has expanded the compositional landscape, unveiling unique structural characteristics for alloy design and providing new prospects for addressing these limitations. Here, we report a compositionally complex NiTi-based composite that exhibits exceptional strength and ductility, along with remarkable recoverable strain. The composite, Ni ₄₀Ti ₄₀(NbMoTaW) ₂₀ (at.%), comprises a 78.0 % B2 NiTi matrix, a 19.2 % Nb-Mo-Ta-W-Ti-Ni compositionally complex body-centered cubic (BCC) phase, and a small amount of Ti ₂Ni. Notably, this composite demonstrates an engineering compressive strength of 3274 MPa, with a compressive fracture strain of 44.2 % and a maximum recoverable strain of 7.3 % (5.6 % elastic strain and 1.7 % inelastic recoverable strain). These outstanding mechanical properties result from the unique structural characteristics of the compositionally complex phase and the lattice strain matching induced by phase transitions. The substantial recoverable strain was obtained through the reversible B2⇌R⇌B19′ phase transition. This work not only innovates a new category of high-performance NiTi-based composites but also extends the applicability of the high-entropy concept.