Effect of element V on the as-cast microstructure and mechanical properties of Al0.4Co0.5VxFeNi high entropy alloys

The as-cast microstructure characteristic and room temperature mechanical properties of Al 0.4 Co 0.5 V x FeNi high-entropy alloys (HEAs, where x = 0, 0.2, 0.4, and 0.6 in molar ratio, denoted as AC0, AC1, AC2, and AC3, respectively), fabricated by the vacuum arc melting method, were investigated by a combination of optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and tension and compression tests. The vertical section of phase diagrams of Al 0.4 Co 0.5 V x FeNi HEAs were calculated with the Pandat software to show the equilibrium phases in the alloys at varying temperatures. The results show that Al 0.4 Co 0.5 V x FeNi HEAs have dual-phase structures. AC0, AC1, and AC2 show a typical dendritic structure composed of dendritic and interdendritic phases. AC3 shows a typical dual-phase structure with the characteristics of a eutectic structure. The comprehensive performance of the Al 0.4 Co 0.5 V x FeNi HEAs is remarkably enhanced by vanadium alloying. AC0 has a microhardness of about 2.79–2.90 GPa, which is three times lower than that of AC3. With an increase of V from 0.4 to 0.6, the structure of FCC-L12 transforms into an FCC phase. The AC1and AC2 HEAs present excellent strength and ductility, with elongation of tension tests at break exceeding 30%. Compared to the tension strength of AC1 and AC2, the yield strength of AC3 increases distinctly and its ultimate strength of extension increases, which is in trade off elongation. The fractured surfaces of AC1 and AC2 are ductile fractures, but the fracture surface feature of AC3 is mainly trench-like microstructures. During tensile deformation, the FCC phase is stretched by ductile fracturing while the BCC-B2 phase shows barely deformed cleavage fracturing, which causes the FCC phase to become thinner and with protruding edges. • Al 0.4 Co 0.5 V 0.6 FeNi HEA show a typical duplex-phase structure with the characteristics of a eutectic structure. • With an increase of V from 0.4 to 0.6, the structure of FCC-L12 transforms into an FCC phase. • The AC1and AC2 HEAs present excellent strength and ductility, with elongation of tension tests at break exceeding 30%.