Synergistic strengthening and toughening of a harmonic-structured (FeCoNi)₈₆Al₇Ti₇ high-entropy alloy via nanoscale precipitation

Achieving a superior strength–ductility synergy remains a critical challenge in the development of high-entropy alloys (HEAs) for advanced structural applications. In this work, a bulk (FeCoNi)₈₆Al₇Ti₇ HEA with a harmonic (heterogeneous core–shell) structure was successfully fabricated by blending gas-atomized coarse and fine pre-alloyed powders at a 1:1 mass ratio, followed by consolidation via spark plasma sintering (SPS). The as-sintered alloy exhibited an ultimate tensile strength (UTS) of 1402.64 MPa with an elongation of 10.59%. To further optimize mechanical performance, systematic aging treatments were conducted at 780 °C for varying durations, and their effects on microstructural evolution and mechanical properties were comprehensively investigated. Aging promoted the uniform precipitation of coherent L1₂ and incoherent L2₁ nanoscale phases within the FCC matrix. Through the synergistic interplay between these nanoprecipitates and the harmonic structure, the alloy aged for 32 h achieved a remarkable combination of high strength and enhanced ductility, with a UTS of ∼1430 MPa and an elongation of ∼22%, representing more than a twofold improvement in ductility compared with the as-sintered state, without loss of strength. The underlying mechanisms, including hetero-deformation induced (HDI) strengthening, precipitation strengthening, and back-stress hardening arising from the heterogeneous microstructure, were elucidated in detail. This study demonstrates that the strategic coupling of powder architecture design (harmonic structure) and precipitation engineering provides a promising pathway to overcome the conventional strength–ductility trade-off in HEAs.