Strain-energy minimization by G/L2₁ core-shell heterostructure enables homogeneous nanoprecipitation in multicomponent alloys

Achieving a high-density and homogeneous dispersion of nanoprecipitates is paramount for strengthening alloys but remains particularly challenging for incoherent phases, which preferentially nucleate heterogeneously at crystal defects (e.g., grain boundary). Here, we report a new pathway to homogeneous precipitation of the typically incoherent G-phase silicide at a high number density with an order of 10²³ m⁻³ in a ferritic steel. This feat is accomplished by forming a core-shell heterostructure, where the G-phase core is encased by a L2₁-Fe₂TiSi shell. Using aberration-corrected scanning transmission electron microscopy, three-dimensional atom reconstruction, and first-principles calculations, we deciphered the atomic structure and interfacial characteristics of this heterostructure. The homogeneous dispersion is enabled primarily by coherent strain energy minimization: the L2₁ shell acts as a buffer layer to mitigate the large lattice mismatch between the G-phase core and the ferritic matrix. Multiple coherent/semi-coherent habit planes at the G/L2₁ interface facilitate effective strain relaxation, thereby significantly lowering the nucleation barrier and promoting intragranular precipitation. Furthermore, chemical intermixing at the interface reduces interfacial energy and suppresses coarsening. This work establishes a novel materials design principle: engineering core-shell heterostructures to manage coherent strain energy can override the conventional interfacial-energy-dominated nucleation paradigm, opening a general pathway to ultra-strong precipitation-hardened alloys.