Designing strong, ductile, and corrosion-resistant high-entropy alloys with dense coherent nanoprecipitation

In the present work, relying on computer-assisted thermodynamic calculations, we developed a series of corrosion-resistant nanoparticles-strengthened high-entropy alloys (HEAs) via elaborately tailoring Cr concentration in the (NiCo)_90−xCr_xAl₅Ti₅ (x = 5–20 at.%) system. The investigated alloys maintain a pure “face-centered cubic + L1₂” dual-phase structure across all these Cr levels, without forming detrimental brittle phases, such as hexagonal close-packed-type intermetallic compounds and σ phases. We found that increasing Cr content effectively enhances yield strength (from 874 to 1016 MPa) and ultimate tensile strength (from 1289 to 1414 MPa) while maintaining a respectable ductility (∼30 %), attributed to the increased volume fraction of L1₂ nanoparticles and reduced lattice mismatch. Crucially, the addition of appropriate levels of Cr (≥ 10 at.%) confers exceptional corrosion resistance to nanoparticles-strengthened HEAs, as evidenced by a sharp rise of pitting potential and reduced corrosion current density in 3.5 wt.% NaCl solution. The multi-scale characterization incorporating X-ray photoelectron spectroscopy, integrated differential phase contrast microscope, and atom probe tomography reveals that higher Cr promotes a continuous, amorphous, nanoscale passive film enriched with Cr₂O₃ (inner layer) and Al₂O₃/TiO₂ (outer layer), alongside a protective Ni-rich sublayer. Such a dual-layer passive film structure underpins the exceptional corrosion resistance.