High-Entropy Alloy: Formation, Microstructure, and Properties

Dear Colleagues,

High-entropy alloys (HEAs) that were developed by mixing equimolar or near-equimolar multiple principal elements into alloys have attracted research attention in recent years. This has opened a new field of “metal harmony” and has been further applied in many fields, such as transportation, structural materials, and biomedical science.

The most remarkable feature of HEAs is their high mechanical performance and their ability to achieve a balance between strength and toughness. Even under extreme conditions, such as high or low temperatures, some HEAs can still maintain high strength and high toughness. The excellent elevated temperature mechanical properties of HEAs produce outstanding wear resistance, while the superior oxidation resistance of HEAs also improves their wear resistance, according to the mild oxidational wear mechanism. In addition, HEAs exhibit good fatigue performance and specific strength.

The material properties of HEAs depend on not only the compositions but also the manufacturing processes. The HEAs’ manufacturing technology can be categorized into four groups, namely, solid-state processing techniques, liquid state processing, thin-film deposition techniques, and additive manufacturing technology. Moreover, the heat treatments of HEAs also considerably influence mechanical properties. The selection of processing methods is important because the performance of HEA products mainly depends on processing methods and their parameters.

Most HEAs produce a single phase with FCC, and/or BCC crystal structures. Some HEAs produce HCP crystal structure. Superior mechanical properties of HEAs can be obtained based on the type of crystal structure formation, the number of phases (single-phase, two-phase, multiphase), and processing routes. However, the phase formation of HEAs is mostly in multiphase (two or more), which also helps to enhance the properties according to the need.

The properties of HEAs are highly influenced by the phase formation, various processing methods, and types of elements present in HEAs. This Special Issue correlates the improvement of properties in terms of phase formations, microstructural variations, and stress-strain curves.

In particular, the topic of interest includes but is not limited to:

• Physical or mechanical properties of HEAs;
• Microstructure evolution of HEAs;
• Phase formations of HEAs;
• Processing methods of HEAs.

Dr. Yu-Chieh Lo
Guest Editors

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