Influence of C14 Laves phase and Zr-rich phase interactions on the hydrogen storage properties of Ti_32.5V_27.5Zr_7.5Nb_32.5 high entropy hydrogen storage alloy

TiVZrNb high entropy alloys possesses excellent hydrogen storage properties as hydrogen storage materials. This is due to the fact that all four elements are composed of hydrogen-absorbing elements with large differences in atomic size. In this study, the effects of C14 Laves phase content and Zr element distribution on the hydrogen storage properties of Ti_32.5V_27.5Zr_7.5Nb_32.5 alloy with different heat treatment time are studied. The as-cast alloy is a single BCC phase, and the structure is dendrites. With the increase of heat treatment time, the alloy shows the transformation of BCC phase to C14 Laves phase and the increase of C14 Laves phase content. And the Zr-rich phase dendrites gradually dissolved with the increase of heat treatment time. The activation time of the alloys decreases with increasing heat treatment time, which is due to the gradual increase of the C14 Laves phase. With the extension of heat treatment time, the low-temperature hydrogen absorption content shows an opposite trend to the high-temperature hydrogen absorption content. This is a result of the major influence of the Zr-rich phase at low temperatures, the significant role of grain boundaries and the C14 Laves phase at high temperatures. In the process of hydrogen absorption, both the BCC phase and the C14 Laves phase participate in the hydrogenation reaction and are mainly transformed into the FCC structure.