Microstructure and corrosion behavior of the Ti-V-Cr-Nb high-entropy alloys in 3.5 wt% NaCl solution

Novel high-entropy alloys (HEAs) of the Ti(30–x)VCrNb(x) (x = 0, 5, 10, 15, and 20 at%) system were designed, synthesized, and characterized. The microstructural features were investigated by XRD, SEM, and EDS. The corrosion behavior was evaluated in 3.5 wt% sodium chloride (NaCl) solution of pH 5 at 25 °C by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The investigated HEAs exhibited a single-phase BCC solid solution with dendritic microstructures. The polarization curves showed the Ti10V35Cr35Nb20 (Nb20) HEA exhibited the best corrosion resistance with the lowest corrosion current density (2.24 µA/cm2) and corrosion rate (1.15 × 10–2 mm/yr). The interpretation of an equivalent electric circuit (EEC) suggested the formation of a stable passive oxide film on the HEAs, as indicated by good capacitive behavior and high impedance values (>104 Ω cm2) at low frequencies and phase angles close to − 80°. This study demonstrated that an appropriate Nb content can stabilize the BCC phase and significantly enhance the corrosion resistance of the HEAs.