Characterizations of Hydrogen Absorption and Surface Properties of Ti 0.2 Zr 0.2 Nb 0.2 V 0.2 Cr 0.17 Fe 0.03 High Entropy Alloy with Dual Phases

In this study, we investigated the microstructures, hydrogen absorption kinetics, and surface oxides of a Ti 0.2 Zr 0.2 Nb 0.2 V 0.2 Cr 0.17 Fe 0.03 high entropy alloy (HEA). The prepared HEA had a dual phase microstructure consisting of body-centered cubic (BCC) phase (32.2Ti-13.1Zr-30.3Nb-18.6 V-5.8Cr) and face-centered cubic (FCC) phase (11.3Ti-19.6Zr-13.2Nb-24.7 V-25.7Cr-5.5Fe). The HEA ingot absorbed hydrogen under a hydrogen pressure of 5 bar at room temperature without any thermal activation process. After hydrogenation, the FCC and BCC phases were transformed to a monohydride and a dihydride phase, respectively. To examine the hydrogen absorption behavior of each phase, two ingots having the same compositions as the BCC and the FCC phases were separately prepared. Though the BCC phase ingot did not react with hydrogen, the FCC phase ingot absorbed hydrogen, which could result from the formation of a highly reactive oxide layer on the FCC phase ingot. From the X-ray photoelectron spectroscopy results of the two ingots, although the BCC phase ingot contained Cr, no Cr was detected in the oxide layer. In contrast, the oxide layer on the FCC phase ingot displayed a high Cr concentration, and it seems that the reactivity of the oxide layer with hydrogen could be improved by the presence of Cr in the surface oxides. Graphic abstract