MICROSTRUCTURAL AND MECHANICAL CHARACTERIZATION OF HYDROGEN-CHARGED Ti5Zr15Fe35Cr25V15Ni5 HIGH-ENTROPY-ALLOY

Hydrogen is widely recognized as a promising clean energy carrier for the transition toward sustainable energy systems. However, the development of safe and efficient hydrogen storage technologies remains a major challenge. Among the available solutions, solid-state hydrogen storage in metallic materials offers significant advantages in terms of safety and volumetric storage density. In this context, High Entropy Alloys (HEAs) have attracted considerable attention due to their compositional flexibility and the possibility of tailoring their microstructure and hydrogen-related properties. The present work investigates the effect of hydrogen on the local mechanical properties of a designed multiphase HEA with nominal composition Ti5Zr15Fe35Cr25V15Ni5 in at.%. The alloy composition was optimized through a CALPHAD-based approach to reduce the solidification range[LM2.1] and promote the formation of a controlled multiphase microstructure consisting of a dominant C14 Laves phase and a secondary BCC phase. The alloy was produced by Vacuum Induction Melting (VIM) and subsequently characterized through microstructural and mechanical analyses. Hydrogen was introduced into the material by electrochemical charging under controlled conditions. The influence of hydrogen on the micro-mechanical properties was evaluated using nanoindentation and Accelerated Property Mapping (XPM), enabling a direct comparison of hardness and reduced elastic modulus before and after hydrogen charging. Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM/EDS), Electron Backscatter Diffraction (EBSD), and X-ray Diffraction (XRD) analyses were performed to correlate mechanical behaviour with phase distribution and microstructural features. The results confirmed the presence of the designed multiphase microstructure and revealed the formation of hydrogen-induced hydride phases after electrochemical charging. Nanoindentation measurements showed an increase in hardness immediately after hydrogen charging, particularly within the C14 Laves phase, indicating a localized hardening effect associated with hydrogen uptake. After 24 hours, a partial reduction in hardness was observed, suggesting hydrogen redistribution or release from the microstructure. Variations in the reduced elastic modulus were less pronounced than those observed for hardness. Overall, this study provides insight into the phase-dependent mechanical response of a multiphase HEA exposed to hydrogen and contributes to the understanding of hydrogen–microstructure interactions in advanced materials for hydrogen storage applications.