Fig. 1. Microstructure of as received Nb-Cr-V-W-Ta HEA. Table shows the overall composition of the alloy as determined by the EDS in SEM. EDS analysis also shows the compositions of the phases at points marked 1 through 5. Color x-ray mapping identifies the locations of dominant metals in various phases.

Fig. 2. Cyclic oxidation curves of Nb-Cr-V-W-Ta HEA at 600, 700, and 800 °C. each cycle is for 12 h of heating. Thus the number of cycles can be converted to heating time.

Fig. 3. Samples after 1 through 6 cycles of heating for 12 h at 600, 700, and 800 °C. Samples are also shown for static heating at 600 and 800 °C for 12 and 24 h. Oxide growth at 800 °C is conspicuous.

Fig. 4. Static oxidation curves of Nb-Cr-V-W-Ta HEA from 600 to1400 °C for 12 and 24 h.

Fig. 5. Static oxidation curves of Nb-Cr-V-W-Ta HEA from 600 to1400 °C at heating rates of 3 and 10 °C to the oxidation temperature. Each heating cycle was for a 24 h duration.

Fig. 6. Samples after oxidation in a range of temperatures from 600 to 1400 °C at a heating rate of 3 °C/min to the oxidation temperature. Figure shows the shapes of the samples after oxidation for 12 and 24 h at the indicated temperatures. a =600 °C, b =800 °C, c =900 °C, d =1000 °C, e =1200 °C, f =1400 °C.

Fig. 7. X-ray mapping for the microstructures of the oxides developed at 1000 °C for 24 h. Crystals of various oxides can be seen.

Fig. 8. X-ray mapping for the microstructures of the oxides developed at 1200 °C for 24 h. Crystals of various oxides can be seen.