Novel (CoFe2NiV0.5Mo0.2)100-xNbx Eutectic High-Entropy Alloys with Excellent Combination of Mechanical and Corrosion Properties

The emergence of eutectic high-entropy alloys (EHEAs) offers new insights into the design of next generation structural alloys, which is due to their stable dual-phase microstructure and outstanding mechanical properties from room to elevated temperatures. In this work, a series of (CoFe2NiV0.5Mo0.2)(100-x)Nb-x (0 <= x <= 12) EHEAs were designed and prepared via vacuum arc-melting. Typical eutectic microstructure composing lamellar face-centered cubic solid solution phase and C14 Laves phase appears in the as-cast EHEA when x = 9. The microstructure turns to hypoeutectic or hypereutectic when x is below or beyond that critical value accordingly. The volume fraction of the hard Laves phase is proportional to the Nb addition, leading to the strength increment yet at the expense of ductility at room temperature. In particular, the EHEA having 4 at% Nb shows a compressive strength of 2.1 GPa with an elongation to fracture of 45%, while EHEAs containing 9 and 10 at% Nb exhibit ultrahigh yield strengths of over 1.4 GPa. The effect of Nb addition on the corrosion resistance of this Cr-free EHEA system was also studied. The EHEA containing 9 at% Nb has the best anti-corrosion performance in the 3.5 wt% NaCl solution at 298 +/- 1 K, indicating a good combination of mechanical and corrosion properties.