A Thermally Stable Hierarchical Heterostructure for Outstanding Impact Resistance in a High-Entropy Alloy

Face-centered cubic high-entropy alloys (FCC HEAs) offer remarkable strain hardening and damage tolerance, yet moderate strength limits their performance under dynamic loading. While nanostructures can largely improve strength, they are thermally unstable. To tackle this dilemma, here we design a thermally stable 3D-heterostructured (FeCoNi) ₈₆ Al ₇ Ti ₇ alloy. The hierarchical heterostructure, consisting of bimodal core-shell architecture (grain sizes: core ~14.4 μm / shell~500 nm), uniformly distributed nano-precipitates and nanosized oxide particles (in shell), remains stable up to 1000 °C. The heterostructured alloy achieves outstanding impact resistance, exhibiting 2.2 GPa yield strength at a strain rate of 5 × 10 ³ s ^-1 . It is demonstrated that the massive martensitic transformation accommodates strain under impact loading, forms networks of nano-martensite that strengthen the material and sustains plasticity. Strain partitioning in the core-shell heterostructures provides potent back-stress hardening, while profuse interfaces facilitate martensite nucleation. The synergy of heterogeneous deformation, precipitation strengthening, and thermally stabilized nanostructures establishes a robust design pathway for alloys with exceptional strength and impact resistance across extreme conditions.