High temperature electrical properties and oxidation resistance of V-Nb-Mo-Ta-W high entropy alloy thin films

Abstract High entropy alloys (HEA) show outstanding thermodynamic, mechanical or thermal properties as compared with pure metals or binary alloys. Among several kinds of HEAs, the refractory element containing HEAs exhibit relatively high thermal stability and better mechanical properties at elevated temperature. In this study, the V19.2Nb19.4Mo20.3Ta19.5W21.6 high entropy alloy thin films were deposited on the AISI 304 stainless steel substrates by a magnetron sputtering process. The oxidation behavior and electrical conductivities of HEA thin films at different temperatures were evaluated. The body-centered cubic (BCC) structure of HEA thin film can be kept up to 500 °C oxidation, and it transferred to V-Nb-Mo-Ta-W based oxides and then turned to iron contained oxide phases when the oxidation temperature increased to 700 °C. The electrical resistivity of thin film increased with oxidation temperature. The electrochemical impedance spectroscope (EIS) analysis showed that the total apparent resistivity values of 304SS substrate coated with V19.2Nb19.4Mo20.3Ta19.5W21.6 high entropy alloy thin film at 600, 700 and 800 °C were 5.80, 6.91, and 7.71 Ω·cm, respectively. The electrical resistance of the HEA coated sample was contributed by the oxide resistance and interface polarization. Through the electrical property analysis at high temperatures, the HEA thin film can provide a protection layer to the 304SS substrate and kept the sample's high temperature apparent resistivity to a relatively lower value.