High impact resistance in a high-entropy alloy with thermally stable hierarchical heterostructures

Face-centred cubic high-entropy alloys offer remarkable strain hardening and damage tolerance, yet moderate strength limits their performance under dynamic loading. While nanostructures can greatly improve strength, they are thermally unstable. Here we design a thermally stable three-dimensional-heterostructured (FeCoNi)₈₆Al₇Ti₇ alloy. The hierarchical heterostructure, consisting of bimodal core-shell architecture, uniformly distributed nanoprecipitates and nanosized oxide particles (in the shell), remains stable up to 1,000 °C. The heterostructured alloy achieves high impact toughness, exhibiting 2.2-GPa yield strength and 1,100-MJ m^-3 energy absorption density at a strain rate of 5 × 10³ s^-1. The massive martensitic transformation accommodates strain under impact loading, forms nano-martensite networks that strengthen the material, and sustains plasticity. Strain partitioning between core and shell 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 high strength and impact toughness across extreme conditions.