High-temperature phase evolution and electrochemical corrosion behaviour of V30Nb16Ta8Cr30Mo16 refractory high-entropy alloy

Abstract The thermal and electrochemical stability of the refractory high-entropy alloy (RHEA) V 30 Nb 16 Ta 8 Cr 30 Mo 16 was systematically investigated to evaluate its suitability for extreme service environments. High-temperature X-ray diffraction (HT-XRD) using a Bruker D8 Advance diffractometer revealed that the alloy retains its dominant BCC solid-solution phases and Cr₂Nb Laves phase up to 1300 °C without evidence of decomposition or new-phase formation under the vacuum conditions tested; oxidation resistance in air was not evaluated in this study. Only minor thermal expansion-related peak shifts were observed, consistent with isotropic lattice expansion without evidence of phase transformation. Corrosion studies conducted in 3.5 wt% NaCl using open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and Tafel polarization indicated stable passivation behaviour. At high anodic potentials, a second, higher current plateau was observed rather than a continued current rise, with no electrochemical evidence of pitting or sustained breakdown within the investigated potential range; further analysis is required to confirm whether this reflects secondary passivation. A low corrosion current density (2.66 × 10⁻⁷ A/cm²), comparable to other Cr/Mo-bearing refractory high-entropy alloys, indicates favourable electrochemical stability. These results demonstrate that V 30 Nb 16 Ta 8 Cr 30 Mo 16 combines good short-term thermal phase stability and room-temperature corrosion resistance, supporting further evaluation of this alloy for high-temperature and marine structural applications.