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

Abstract

The effect of Nb addition in arc‐melted CoCrFeNiNbx (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 CoCrFeNiNb0.5 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 CoCrFeNiNbx and other eutectic HEAs as reported in the literature, has been assessed by estimating mixing entropy (ΔSmix), mixing enthalpy (ΔHmix), atomic size differences (δ), valence electron concentration, Pauling electronegativity (ΔχP), and Allen electronegativity (ΔχA) to predict the evolution and coexistence of eutectic phases.