Characterizations of Hydrogen Absorption and Surface Properties of Ti0.2Zr0.2Nb0.2V0.2Cr0.17Fe0.03 High Entropy Alloy with Dual Phases

Abstract

In this study, we investigated the microstructures, hydrogen absorption kinetics, and surface oxides of aTi0.2Zr0.2Nb0.2V0.2Cr0.17Fe0.03high entropy alloy (HEA). The prepared HEA had a dual phase microstructure consistingof 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 roomtemperature without any thermal activation process. After hydrogenation, the FCC and BCC phases were transformed to amonohydride and a dihydride phase, respectively. To examine the hydrogen absorption behavior of each phase, two ingotshaving the same compositions as the BCC and the FCC phases were separately prepared. Though the BCC phase ingot didnot react with hydrogen, the FCC phase ingot absorbed hydrogen, which could result from the formation of a highly reactiveoxide layer on the FCC phase ingot. From the X-ray photoelectron spectroscopy results of the two ingots, although theBCC phase ingot contained Cr, no Cr was detected in the oxide layer. In contrast, the oxide layer on the FCC phase ingotdisplayed a high Cr concentration, and it seems that the reactivity of the oxide layer with hydrogen could be improved bythe presence of Cr in the surface oxides.