Effect of phase composition and cluster structure on de-/hydriding kinetics of as-cast and heat-treated Ti33V37Mn30-xCrx alloys

Abstract

To enhance the hydrogen storage property, elements Mn in Ti₃₃V₃₇Mn₃₀ alloy were partially substituted with varying concentrations of elements Cr. The Ti₃₃V₃₇Mn₂₄Cr₆ variant, which exhibited superior performance, was selected for further analysis. Ti₃₃V₃₇Mn₂₄Cr₆ samples were first heat-treated separately at 773K, 973K and 1173K for 2h, and then water-quenched. The effect of Cr substitution and heat treatment on the microstructure and de-/hydriding properties of Ti₃₃V₃₇Mn_30-xCr_x alloys were investigated. As-cast alloys were composed of BCC phases mainly, along with some C14 Laves phases and Ti-rich phases. The lattice parameter of BCC phases in Ti₃₃V₃₇Mn₂₄Cr₆ increased to 3.053 Å. Cr substitution changed the tetrahedral gap of the alloy. At 298K, the initial hydrogen absorption capacity and the maximum hydrogen desorption capacity of Ti₃₃V₃₇Mn₂₄Cr₆ were raised to 3.07 wt% and 1.81 wt%, respectively. The lattice parameter of Ti₃₃V₃₇Mn₂₄Cr₆ alloys heat-treated at 773K also enlarged to 3.056 Å. Elevating the heat treatment temperature to 973K and 1173K significantly raised the proportion of C14 Laves phases in the alloy. Hydrogen storage performance of heat-treated alloys was examined at 298K. The results suggested that the heat-treated alloys could be fully activated after one hydrogen ab-/desorption cycle. Ti₃₃V₃₇Mn₂₄Cr₆ alloy heat-treated at 773K achieved the maximum hydrogen desorption capacity of 1.83 wt%, with an accelerated hydrogen ab-/desorption rate.