Excellent strength-ductility synergy enabled by modulating grain heterogeneity in a tri-modal heterostructured CoCrNi multi-principal element alloy with highly retained deformed grains

Abstract The rational design of metallic materials with simultaneous ultrahigh strength and high ductility remains a fundamental challenge, as conventional strengthening strategies often exacerbate plastic instability. Here, we reveal that this trade-off can be overcome in a single-phase tri-modal heterostructured CoCrNi multi-principal element alloy with a high fraction of deformed grains by modulating grain heterogeneity. Synthesized via precisely controlled sub-critical annealing, this structure, comprising deformed grains (DGs, ∼22.5%), fine grains (FGs, ∼22.5%), and ultrafine grains (UFGs, ∼55.0%), delivers exceptional yield strength of 1.35 GPa and elongation of 33.4%. This synergistic effect originates from the sequential activation of strengthening mechanisms: initially triggered by the formation of deformation twins (DTs) and Lomer–Cottrell locks within the FGs at 5% strain, followed by the generation of DTs within the UFGs at 20% strain. Such a sequentially activated process promotes sustained hetero-deformation induced stress within the tri-modal heterostructure, providing the essential strain-hardening increment and thereby effectively circumventing the premature saturation typical of bi-modal heterostructures. This unique structural design satisfies the requirements for prolonged strain hardening at ultrahigh stress levels, offering a viable paradigm for exploiting hierarchical heterogeneity to activate staged deformation sequences in high-performance structural alloys.