An assessment on the stability of the eutectic phases in high entropy alloys

Abstract To overcome the limited mechanical properties of single-phase FCC/BCC high entropy alloys, a large effort is being made towards the development of eutectic composites. The eutectic/near eutectic high entropy alloys (EHEAs) with alternate lamellar phases provide an optimum balance between strength and ductility. Therefore, CoCrFeNiNb x (0.45  x  0.65) and CoCrFeNiTa y (0.2  y 2 Nb/Co 2 Nb type Laves phase were synthesized by arc-melting and were characterized by x-ray diffraction, scanning electron microscopy and energy dispersive x-ray spectroscopy. Furthermore, a large number of EHEAs comprising of BCC/FCC solid solution phases and intermetallic compound/topologically closed packed (TCP) phases have been surveyed, as reported in the literature. The stability of the phases were assessed by considering the mixing enthalpy (Δ H mix ), valence electron concentration ( VEC ), and atomic size difference ( δ r ). The eutectic phases in all these EHEAs become stable when −18 ≤ Δ H mix  ≤ −6, 6 ≤  VEC ≤ 8.5 and δ r > 3%. The synergistic effect of Δ H mix , VEC, and δ r on the phase stability and the phase prediction in EHEAs, have been explored.