ABSTRACT Simultaneously achieving high strength, adequate ductility, and low anisotropy remains challenging for additively manufactured medium‐entropy alloys (MEAs), particularly without relying on post‐processing. Here, a Co 28 Cr 18 Ni 42 Al 6 Ti 6 MEA was fabricated by laser‐directed energy deposition (LDED), enabling effective in situ strengthening through nonequilibrium solidification and intrinsic thermal cycling. As a result, a hierarchical microstructure was developed, consisting of fine‐grain clusters enriched with high‐angle grain boundaries, coherent L1 2 nanoprecipitates, and distinctive γ‐Al 2 O 3 /β‐Ti core–shell structures. Fine‐grain clusters together with spatially distributed heterogeneities contributes to the reduced mechanical anisotropy. As a result, the alloy exhibited high strength while retaining good ductility, exhibiting yield strengths of 880 ± 6.2 MPa and 850 ± 7.2 MPa, ultimate tensile strengths of 1200 ± 32.1 MPa and 1150 ± 55.4 MPa, and fracture elongations of 19% ± 3.5% and 21% ± 5.5% along the building and scanning directions, respectively. The enhanced mechanical performance was attributed to multiscale strengthening arising from the synergistic L1 2 nanoprecipitates and core–shell structures, which impeded dislocation motion across multiple length scales while accommodating interfacial strain, thereby sustaining work hardening and retaining ductility.
Wang et al. (Fri,) studied this question.