Structure analysis (XRD and Neutrons) and hydrogen storage properties of Hf1-Ti NbVZr BCC high entropy alloys

The hydrogen storage properties of Hf 1- x Ti x NbVZr high entropy alloys (HEAs) synthesized by arc melting have been investigated. The first hydrogenation of the alloys was performed at room temperature under 20 bars of hydrogen pressure. Results show an increase in gravimetric hydrogen content with Ti substitutions. Upon hydrogenation, the multiphase alloys ( x = 0 and x = 0.25) exhibit a combination of faces-centred-cubic (FCC) hydride and C15 Laves phases, while single-phase alloys ( x = 0.5, 0.75, and 1) display FCC structures. The crystal structure evolution during dehydrogenation of HfNbVZr ( x = 0) and TiNbVZr ( x = 1) HEAs was examined using in-situ neutron diffraction. The analysis demonstrates temperature-dependent desorption behaviour, with HfNbVZr displaying lower desorption temperatures compared to TiNbVZr. Additionally, in-situ neutron diffraction experiments during deuterium desorption indicate a two-step phase transition from FCC dihydride to BCT monohydride, followed by a transition to BCC. • Ti substitution enhances gravimetric hydrogen capacity in Hf 1- x Ti x NbVZr HEAs. • Room temperature hydrogenation forms multiphase and single-phase structures. • HfNbVZr desorbs hydrogen at lower temperatures than TiNbVZr. • Neutron diffraction shows FCC to BCT to BCC phase transitions. • Results improve understanding of HEAs for hydrogen storage