ADevelopment of refractory High Entropy Alloys: relationship between composition, structure, hydrogen absorption properties and corrosion resistance properties.

This study investigates light High Entropy Alloys (HEAs) Ti₂₅V₂₅Nb_25-xCr_25-xAl_2x and Ti₂₅V₂₅Nb_25-xFe_25-xAl_2x with compositions designed based on empirical criteria including valence electron concentration (VEC), mixing entropy, and enthalpy. The objective is to evaluate the impact of aluminium content on alloy structure, hydrogen sorption, and corrosion resistance. Substituting chromium with iron modifies the phase composition: chromium-based alloys exhibit a single BCC phase, while iron-containing alloys form multiphase structures (C14 + C15 + BCC). Increasing the aluminium content improves the corrosion resistance of chromium-based alloys, with a shift in corrosion potential (Ecorr) from –447.9 mV to –12.2 mV. The multiphase nature of iron-containing alloys promotes galvanic coupling, reducing corrosion resistance but enhancing hydrogen absorption. Iron-based alloys absorb between 1.0 and 1.5 wt.% hydrogen under standard conditions, whereas chromium-based alloys show negligible absorption unless pre-activated by ball milling under hydrogen, after which they reach 2.4 wt.%. Ageing tests show that surface oxidation reduces hydrogen absorption capacity, from 2.4 wt.% to 1.8 wt.%, and slows sorption kinetics. These findings highlight the importance of storage conditions and alloy ageing on the reproducibility of hydrogen storage properties. Electrochemical analyses provide complementary insights into the behaviour and performance of these HEAs.