Preparation-Dependent Microstructure and Hydrogen Storage in High-Entropy Alloys

Area of Science:

• Materials Science
• Solid-State Chemistry
• Hydrogen Storage Technologies

Background:

• High-entropy alloys (HEAs) show promise for solid-state hydrogen storage due to tunable properties.
• Hydrogen storage behavior in HEAs is complex and not solely predictable by composition.
• The preparation method significantly impacts the resulting microstructure and thus performance.

Purpose of the Study:

• To examine how different preparation routes influence the microstructural states of HEAs.
• To correlate these distinct structural states with hydrogen accommodation, diffusion, and reversibility.
• To evaluate key structural descriptors for understanding hydrogen storage in HEAs.

Main Methods:

• Analysis of HEAs prepared via arc melting and homogenization.
• Investigation of HEAs produced by mechanical alloying and reactive ball milling.
• Evaluation of structural descriptors: phase constitution, grain size, defect density, and chemical homogeneity.

Main Results:

• Arc melting yields bulk alloys with simpler average phase constitutions.
• Mechanical alloying and ball milling produce defect-rich, metastable, non-equilibrium structures.
• Similar compositions exhibit different hydriding pathways based on their realized structural state.

Conclusions:

• Microstructure, determined by preparation route, is the critical factor governing HEA hydrogen storage.
• Future advancements require focusing on microstructure-hydrogen-storage relationships over composition screening alone.
• Developing transferable relationships across route-defined structural states is key for progress.