High-Entropy Alloy and Compositionally Complex Alloys: Challenges and Prospects for Applications in Corrosive Environments

Dear Colleagues,

In the last decade, high-entropy alloys (HEAs) have gained increased attention as a new class of metallic materials with improved mechanical properties and corrosion resistance for environments where high-temperature strength and corrosive challenges prevail. HEAs are multi-component alloys which consist of equiatomic mixtures or near-equal proportions of five or more elements. They tend to form simple solid-solution structures due to their high mixing entropy, with single-phase crystal structures being more studied. The sluggish diffusion and severe lattice distortions of HEAs have a large effect on their microstructures and properties. These characteristics are considered to be of critical importance for providing the good properties of HEAs, such as high hardness and strength, corrosion, and wear resistance.

Recently, distinction has been made between single-phase high-entropy alloys and multi-phase compositionally complex alloys (CCAs), which both fulfill the initial definition criteria. There are many different kinds of multi-component alloys. Whether they have a large number of components in equal or near-equal proportions depends on their alloying method, constituent species, manufacturing method, and resulting phase structure and microstructure. The combination of the unique structure, excellent mechanical properties, and corrosion and oxidation resistance have given these materials a position as promising candidates for structural applications in corrosive environments. These application fields can be various, including: geothermal, oil and gas, and nuclear industry, biomedical coatings, electronics industry, and lightweight casing for mobile facilities, battery anode materials, and the transportation industry.

The requirement for near-equiatomic mixtures can also lead to the high cost of these alloys if more exotic or costly elements are required. The deposition of HEAs and CCAs as a coating onto an inexpensive substrate could be an economical way to exploit the advantageous properties of these materials.

This Special Issue welcomes original research on topics concerning the microstructure, corrosion resistance, and mechanical properties of different types of bulk HEA and CCA materials, as well as coatings based on these constitutes. This includes characterization of the HEAs obtained from the thermodynamical point of view, microstructural (SEM/EDS) and crystal structural (XRD) analysis, as well as mechanical and corrosion testing, or any relevant test that will prove the hypothesis and results presented.

We hope that this Special Issue will provide a platform to share new results on the properties and structure of HEAs and CCAs for coatings and bulk materials.

Prof. Dr. Sigrún Nanna Karlsdóttir
Prof. Ioana Csaki
Guest Editors

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