Microstructure, hardness, oxidation, and corrosion behavior of TiNbTaVW refractory high entropy alloy in 3.5 wt% NaCl and 1 M H2SO4

Abstract

Refractory high entropy alloys (RHEAs), which comprise high-melting-point refractory elements, have been regarded as potential candidates that can substitute nickel-based superalloys used in high-temperature applications. This study investigated the microstructure, hardness, corrosion, and oxidation behavior of the TiNbTaVW RHEA compared with commercial-grade IN718 alloy. The equiatomic TiNbTaVW RHEA was produced using an arc melting furnace. The microstructure of the as-cast RHEA consisted of a body-centered cubic solid-solution phase with a dendritic structure corresponding to the empirical phase prediction. The RHEA exhibited a higher hardness of 522 ± 10 HV than the IN718 alloy with 301 ± 14 HV. The higher hardness is due to solid-solution strengthening and grain refinement. The RHEA had a lower corrosion rate in 3.5 wt% NaCl (0.0003 mm/yr) and 1 M H2SO4 (0.0009 mm/yr) than the commercial IN718 alloy (0.054 mm/yr and 1.12 mm/yr, respectively). At 850 °C after 15 h and 1050 °C after 15 h, the IN718 alloy exhibited a mass gain of 4.41 mg/cm2 and 10.84 mg/cm2, respectively, while the TiNbTaVW RHEA exhibited a mass loss of − 23.58 mg/cm2 and − 45.92 mg/cm2, respectively, indicating that the IN718 alloy exhibited the best oxidation resistance. Thermal and growth stresses contributed to the pores, voids, cracks, and oxide layer spallation observed in the TiNbTaVW RHEA.