Design of metastable complex-concentrated alloys through composition tailoring

To develop alloys with high strength and reasonable ductility, CoCrFeNi-based metastable complex-concentrated alloys were designed using composition–property contour maps. The map was constructed by exploring the phase stability and mechanical behaviors of a series of CoCrFeNi alloy thin films synthesized via solid-state alloying of multilayer thin films. The concentrations of Co and Ni were key to activate metastable deformation behaviors by reducing the stacking fault energy of alloys and improve solid-solution strengthening, as expected from the atomic-level complexity related to the electronegativity difference. By optimizing the Co and Ni concentrations based on the composition-phase/mechanical property contour maps, we activated the combined deformation behavior of mechanical twinning and phase transformation. This resulted in a Co₃₃Cr₂₅Fe₂₅Ni₁₇ metastable complex-concentrated alloy with excellent tensile properties—yield strength of 234 MPa, ultimate tensile strength of 720 MPa, and elongation to failure of 80%. The proposed approach provides a useful guideline for the design of complex-concentrated alloys with customized properties through property predictive control.