Electronic-structure-driven intrinsic toughening and nanoscale B2/L2₁ ordering in Cu-Zr-based dual-phase alloys

The contradiction between ultra-high strength and high ductility remains a critical challenge in structural materials. Here, a design strategy based on the electronic density of states is proposed to intrinsically toughen the brittle long-range ordered phases that inevitably precipitate during fabrication of large-sized metallic glass composites. Using the Cu-Zr system as a model, Nb is introduced based on the valence electron concentration compensation principle. Surplus Nb-4d electrons precisely fill the pseudogap at the Fermi level, transforming rigid covalent bonds into flexible metallic bonds. This electronic-state softening not only promotes the formation of a fully coherent nanoscale structure made up of B2 and L2₁ phases, but also lowers the generalized stacking fault energy by 64% while preserving the ideal work of separation. As a result, the Rice-Thomson ductility index rises from approximately 2.1 to 6.2, creating a pathway for macroscopic coherent slip transmission. Molecular dynamics simulations further show that L2₁ ordering takes place through diffusionless rearrangement within a single lattice constant. Overall, this work converts the toughening challenge into a predictable electron-transfer strategy, offering new templates for strengthening advanced materials that are limited by brittle phases.