Composition Dependence on the Evolution of Nanoeutectic in CoCrFeNiNb_x (0.45 ≤ x ≤ 0.65) High Entropy Alloys

The effect of Nb addition in arc‐melted CoCrFeNiNb_x (0.45 ≤ x ≤ 0.65) high entropy alloys (HEAs) on the phase evolution, stability, refinement of the microstructure, and mechanical properties are investigated. Minor fluctuation of Nb modifies the microstructure from hypoeutectic (x = 0.45) to eutectic (x = 0.5) and hypereutectic (x = 0.55) containing 134–200 nm thin nano‐lamellar FCC γ‐Ni and HCP Fe₂Nb‐type Laves phases. The nano‐eutectic CoCrFeNiNb_0.5 HEA shows high yield strength (2060 ± 5 MPa) and strain hardening up to 2200 ± 10 MPa with 17.0 ± 0.5% compressive plasticity. Transmission electron microscopic studies of partially deformed specimen has been revealed that the activity of dislocations is present in the eutectic FCC/Laves lamellae and at their interface. The stability of the phases in CoCrFeNiNb_x and other eutectic HEAs as reported in the literature, has been assessed by estimating mixing entropy (ΔS_mix), mixing enthalpy (ΔH_mix), atomic size differences (δ), valence electron concentration, Pauling electronegativity (Δχ_P), and Allen electronegativity (Δχ_A) to predict the evolution and coexistence of eutectic phases.