Design of a nickel–cobalt based eutectic high entropy alloy (NiCo)<inf>1.7</inf>AlCrFe with hierarchical microstructural length scales

A combined nickel–cobalt-based eutectic high entropy alloy (Ni-Co-based HEA) has been designed based on the valence electron concentration (VEC) value. The microstructure of the developed alloy consists of a face-centered cubic (FCC) and ordered cubic (B2) structure, which was validated using CALPHAD. The microstructure is hierarchical with length scales in micrometers (lamellar eutectic morphology) and nanometers (B2 length scale). B2 phase precipitation was observed in the supersaturated FCC primary phase. The orientation relationship (OR) between the phases exhibited a strong Kurdjimov-Sachs (KS) type OR, typical of FCC/BCC interface structures. This EHEA displayed good yield strength at room temperature and strain rate insensitivity in the 10−3–10−1 strain rate range.