The role of solid-state phase transformation mechanisms on the hydrogenation of multicomponent TiZrFeNi and Ni-Zr binary alloys

This study investigates solid-state phase transformations during hydrogenation of multicomponent TiZrFeNi and Ni-Zr binary alloys sharing the Ni 10 Zr 7 phase. The multicomponent alloy was designed using semi-empirical criteria and predicted by CALPHAD calculations. The phase equilibria revealed that it crystallizes into a dual-phase microstructure comprising C14 Laves and Ni 10 Zr 7 phases, with an elemental gradient. Both TiZrFeNi and Ni-Zr alloys (C1 and C2) rapidly absorb hydrogen at room temperature, without thermal activation for the C1 and C2 compounds. PCI curves reveal high hydrogen solubility in the α-Ni 11 Zr 7 phase, while steep regions at higher pressures suggest γ-hydride formation. A hydrogen-induced transformation (HIT) is observed in Ni 11 Zr 9 phase, converting it to NiZr during the first hydrogenation and thereby affecting absorption kinetics. The hydrogen storage capacity of TiZrFeNi is attributed to the combined contribution of C14 Laves and Ni 11 Zr 7 phases. These results highlight HIT as a key mechanism governing hydrogen absorption of the phases present in C14 Laves alloys. The findings contribute to a better understanding of the role of secondary intermetallic phases in the hydrogen storage properties of multicomponent alloys by elucidating the phase transformation during hydrogenation and its impact on the properties of TiZrFeNi alloy.