Quantitative neutron characterization of dislocation-nanoprecipitate synergistic strengthening in additively manufactured FeCoNiAlTi high-entropy alloy with ultrahigh yield strength

Introducing dislocations and nanoprecipitates is an effective strategy to strengthen alloys, but reliable bulk quantification of dislocation density and coherent nanoprecipitate content remains challenging. Here, FeCoNiAlTi high-entropy alloys with high-density dislocation network and coherent nanoprecipitates were fabricated by selective laser melting and subsequent aging. Neutron diffraction reveals that aging introduces ∼35 vol% coherent L1₂ nanoprecipitates with an ultralow lattice mismatch (∼0.050%) to the FCC matrix. Small-angle neutron scattering determines an average radius of ∼10.2 nm for the L1₂ nanoprecipitates. Line-profile analysis shows the dislocation density decreases from (13.9 ± 0.3) × 10¹⁴ m⁻² in the as-built state to (6.1 ± 0.1) × 10¹⁴ m⁻² after aging. Correspondingly, the yield strength increases to 1300 ± 20 MPa, dominated by the synergistic strengthening of L1₂ nanoprecipitation (618 MPa) and dislocation hardening (310 MPa). This work establishes a quantitative correlation between dislocation structures, coherent nanoprecipitation and mechanical performance in additively manufactured HEAs.