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Description
Medium-entropy alloys (MEAs) are multi-principal element systems in near-equimolar ratios (5 – 35 at. %) that provide a versatile platform for the development of solid-state hydrogen storage materials. In particular, alloys with a body-centered cubic (BCC) structure are attractive due to their high density of interstitial sites available for hydrogen accommodation. This study investigates a series of heat-treated (TiZrNbTa)100−xAlx medium-entropy alloys (x = 0 - 10 at. %) to evaluate the influence of aluminum addition on microstructure, mechanical response, and hydrogen sorption behaviour.
The alloys were prepared by arc melting followed by homogenization heat treatment and characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), density measurements, microhardness testing (HV0.2), nanoindentation, and hydrogen sorption measurements under isobaric conditions. Aluminum addition systematically modified the microstructure, resulting in pronounced changes in phase morphology. Increasing Al content reduced alloy density, while hardness and elastic modulus exhibited composition-dependent, non-linear trends. Hydrogen absorption behaviour was strongly influenced by alloy composition, affecting both activation temperature and hydrogen storage capacity during repeated absorption cycles.
Among the investigated compositions, the alloy containing 5 at. % Al exhibited the most balanced combination of hydrogen capacity, activation characteristics, and mechanical stability, demonstrating its potential as a promising candidate for hydrogen storage applications. These results highlight the importance of controlled alloy design in optimizing the performance of TiZrNbTa-based medium-entropy alloys for solid-state hydrogen storage.
Acknowledgements
This work was supported by the Slovak Research and Development Agency under Contract No. APVV-23-0030, VEGA Project No. 1/0122/25, KEGA Project No. 011TUKE-4/2025, and under Contract No. VV-MVP-24-0264. This research was funded in part by the international project M-ERA.NET 3/2022/235/H2MobilHydride. This work was also supported by the Technology Agency of the Czech Republic under the THÉTA 2 Programme, Project No. TS02030229, High-Entropy Alloys for Sustainable and Efficient Hydrogen Technologies, co-financed from the state budget of the Czech Republic. The authors also acknowledge the support of the Early Stage Grants TUKE (ESG TUKE) project, funded by the European Union – NextGenerationEU through the Recovery and Resilience Plan of the Slovak Republic under Project No. 09I03-03-V05-00015.
