Microstructures and hydrogenation properties of (ZrTi)(V_1-xAl_x)₂ Laves phase intermetallic compounds

Abstract In this work, the (ZrTi)(V_1-xAl_x)₂ (x = 0.02, 0.05, 0.10, 0.15, 0.25) Laves phase intermetallic compounds were prepared by the arc-melting method. The microstructure and phase compositions were examined by SEM and XRD. Hydrogen absorption pressure composition isotherms (P-C isotherms) were obtained by the pressure reduction method using a Sievert type apparatus at different temperatures. The thermodynamic and kinetic properties of the alloys were investigated in this work. The results show that the (ZrTi)(V_1-xAl_x)₂ alloys consist of a dominant C15 Laves phase with cubic structure and a V-based solid solution phase with BCC structure. With further increasing Al content, C15 cubic type Laves phase and C14 hexagonal type Laves phase coexist in the range x ≥ 0.15 in this (ZrTi)(V_1-xAl_x)₂ alloys. The crystal lattice parameter of the C15 phase increases with the increase of Al content. The PCT curves give the evidence that the maximum hydrogen absorption capacity decreases with the increase of Al content, which results from the existence of ZrAl₂ which hardly absorb hydrogen. There is no obvious hysteresis between absorption and desorption in the (ZrTi)(V_1-xAl_x)₂ alloys at 823 K. The (ZrTi)(V_1-xAl_x)₂ alloys with x = 0.25 preserves higher temperature of phase transformation (β → α). The existence of C14 phase (including ZrV₂ and ZrAl₂) decreases the stability of hydrides.