Additively manufactured heterogeneous precipitation-strengthened high-entropy alloys with high strength and ductility

Heterogeneous-structured (HS) materials have drawn particular attention due to their extraordinary strength-ductility combinations. Benefiting from the large thermal gradient and high cooling rate, additive manufacturing (AM) enables structural and compositional heterogeneity at the multiscale, which provides new routines for high-performance HS materials. Here, we successfully fabricated a cellular-structured CoNiCrFeAlTi-based high-entropy alloy (HEA) by using the directed-energy deposition (DED) technology. Subsequent thermal treatment produces a distinctly different microstructure consisting of single-phase (face-centered cubic, FCC) interior and dual-phase (FCC + L12) wall, which leads to an ultrahigh tensile strength of ∼1148 MPa combined with a large ductility of ∼28 %. We attribute the high strength to the pronounced ordering strengthening from high-density L12-type precipitates in the wall while the large ductility primarily comes from the improved plastic deformation stability via hetero-deformation-induced strain hardening and deformation-induced stacking faults (SFs). Our current work is expected to open up a new area for designing high-performance HS multiple-principal-element alloys.