Hierarchical Deformation Pathways Enable Multistage Strain Hardening in an Oxide-Dispersion-Strengthened Alloy

Oxide-dispersion-strengthening is a well-established strategy to enhance yield strength in metallic systems, but typically at the expense of ductility due to limited strain hardening. Here, we report a multistage strain hardening mechanism in an in situ formed ultrafine-grained oxide-dispersion-strengthened (ODS) Ni₅₀Co₃₅V₁₅ multiprincipal element alloy, which simultaneously achieves ultrahigh yield strength of 1326 ± 26 MPa, an enhanced yield-to-ultimate strength difference of 189 MPa, and an elongation of 12.1 ± 0.6%. This behavior arises from the sequential activation of distinct deformation substructures─ranging from planar dislocation slip bands and dislocation networks to hierarchical stacking faults and Lomer-Cottrell locks─whose interactions with dispersed nano-oxides sustain plasticity through successive stages of deformation. We show that structural heterogeneity, compositional inhomogeneity, and grain size disparity collectively enable strain-dependent transitions in hardening mechanisms. Our findings reveal a previously unrecognized synergy between dispersed oxides and evolving dislocation substructures, offering a generalizable pathway to overcome the strength-ductility trade-off in high-strength metallic materials.