Deformable precipitates locally modify fault-mediated plasticity for strength-ductility synergy

Precipitates in structural alloys are conventionally understood as passive obstacles to dislocation motion. Here we show that semi-coherent hexagonal close-packed precipitates in a low-stacking-fault-energy Ni50Co30Ru20 multi-principal element alloy cooperate with planar-fault plasticity in the face-centered cubic matrix. In-situ neutron diffraction, high-resolution electron microscopy, and first-principles calculations reveal that these precipitates interact with and locally modify Shockley-partial-mediated fault structures, are associated with confined, deformation-related interfacial stacking rearrangement, and generate heterogeneous stress fields that sustain work hardening. Phase-resolved diffraction shows that the precipitates yield at an applied stress of ∼1020 MPa and that the load they carry directly is bounded at ∼6–10% of the yield strength, so their contribution mainly acts through the precipitate-matrix interfaces, resulting in a tensile strength of 1038 MPa and 39% uniform elongation. These findings establish a design strategy: coupling low fault energy with deformable phase heterogeneity amplifies planar-fault-mediated strain hardening.Impact statementSemi-coherent precipitates interact with and locally modify planar-fault plasticity, accommodating interfacial rearrangements, and sustaining heterogeneous stress fields, suggesting a design strategy for strong and ductile alloys.