Additively manufactured high strength-ductility 9Cr ODS alloy: Inducing multi-heterogeneous structure via Y₆WO₁₂@W core-shell nanoscale precursor

Overcoming the strength-ductility trade-off in additively manufactured 9Cr oxide dispersion strengthened (ODS) alloys is a significant challenge in structural materials design. In this work, multi-heterogeneous microstructures are orchestrated to overcome the strength-ductility trade-off by employing Y₆WO₁₂@W (YWO@W) nanoscale core-shell precursor. The multi-heterogeneous structures comprise YWO@W/YWO nanoparticles (NPs), bimodal grains, heterogeneous defects, and heterogeneous deformation zones. The W shell alleviates the density mismatch between YWO NPs and molten matrix, thereby suppressing YWO NPs flotation during additive manufacturing. Concurrently, partial dissolution of W triggers asynchronous martensitic transformations and forms heterogeneous defect zones. The heterogeneous structure interfaces generate substantial geometrically necessary dislocations, resulting in a back stress strengthening of 357 MPa. The uniformly dispersed ∼25 nm YWO/YWO@W NPs provide a contribution of 123 MPa from Orowan strengthening. Quantitative strengthening modeling incorporating Orowan, grain boundary, dislocation, solid solution and back stress contributions predicts a yield strength of 880 MPa, consistent with experimental measurements. During plastic deformation, the low-defect and deformation zones within the heterogeneous structures facilitate dislocation storage, while the YWO/YWO@W NPs promote dislocation cross-slip. The non-coherent interface between YWO NPs and the matrix may induce dislocation slip along the {1 2 1}<1 1 1> system, which in turn enables multi-slip systems to operate simultaneously. Finally, the YWO@W sample exhibits tensile strength of 1214 MPa and elongation of 10.3%, representing increases of 45.6% and 145.2%, respectively, compared to Y₂O₃ sample. This work offers a novel strategy to overcome the strength-ductility trade-off in additively manufactured ODS alloys.