Synthesis and Hydrogen Decrepitation of High-Entropy TiVCrNbZr and TiVCrNbCo Alloys

Abstract

This study reports the synthesis and structural characterization of two equimolar high-entropy alloys, TiVCrNbCo and TiVCrNbZr, which are promising hydrogen storage materials. The alloys were produced via vacuum arc melting of elemental powders under an argon atmosphere; then their phase composition and microstructure were characterized using X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM–EDS), both before and after hydrogen decrepitation (HD process). The TiVCrNbCo alloy predominantly crystallizes in the hexagonal Laves C14 phase, whereas the TiVCrNbZr alloy forms a structure consisting whereas the TiVCrNbZr alloy forms a structure consisting of mixtures of cubic Laves C15 and body-centered cubic (BCC) phases. Hydrogen process transforms both alloys into finely dispersed powders, leaving residual hydrogen contents of 0.19 wt % for TiVCrNbCo and 1.8 wt % for TiVCrNbZr. Phase analysis after HD process shows that TiVCrNbCo retains the hexagonal C14 phase along with a secondary C14 + H phase, which likely corresponds to a solid solution of hydrogen. In contrast, the HD-crushed TiVCrNbZr powder contains the cubic Laves C15 phase and an face-centered cubic (FCC), phase, indicating a BCC-to-FCC transformation characteristic of hydrogenation-induced structural changes. In situ XRD measurements reveal no significant structural rearrangement upon heating of the HD-crushed samples; however, clear changes in reflection intensities are observed due to thermal lattice expansion and progressive hydrogen desorption. Hydrogen release occurs at approximately 200°C for TiVCrNbCo and 500°C for TiVCrNbZr.