Editorial Feature

What Are High Entropy Alloys?

High entropy alloys (HEAs) are a novel class of metallic materials that have attracted significant attention in the materials science community in recent years due to their unique combination of mechanical, thermal, and physical properties.

What Are High Entropy Alloys?

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An Introduction to High Entropy Alloys

The term “high entropy” refers to the fact that these alloys contain five or more elements in roughly equal amounts, resulting in a complex microstructure and high configurational entropy.

This high configurational entropy results from the presence of many different types of atoms in the alloys, which leads to complex and heterogeneous structures that can be manipulated to achieve desirable properties.

High entropy alloys are typically composed of elements with different crystal structures and exhibit several unique properties compared to conventional alloys. HEAs often possess high strength, hardness, wear resistance, thermal stability, and corrosion resistance.

They can exhibit improved thermal and electrical conductivity and magnetic properties, making them suitable for a wide range of applications in various fields, such as aerospace, energy, transportation, and biomedical engineering.

HEAs are typically produced through various synthesis methods, such as casting, powder metallurgy, and mechanical alloying.

The properties of HEAs can be tailored through variations in composition, microstructure, and processing conditions. For instance, the microstructure of HEAs can be controlled by adjusting the processing conditions, including temperature, cooling rate, and heat treatment.

This enables engineers to produce HEAs with specific mechanical, thermal, electrical, and magnetic properties that are optimized for specific applications.

Applications of High Entropy Alloys

High entropy alloys have been identified as having potential for a wide range of applications due to their unique combination of mechanical, thermal, and physical properties.

As indicated by Dada, HEAs may be used for high-temperature applications, such as in jet engines and hypersonic vehicles, due to their high-temperature strength and thermal stability.

High entropy alloys have also been considered for use in automotive applications due to their high strength and toughness, making them suitable for structural components, such as engine parts, suspension systems, and drivetrain components.

Another area in which HEAs can play an important role is orthopedic implants. de Oliveira showed that HEAs have excellent corrosion resistance and biocompatibility, making them suitable for use as biomaterials for medical applications.

Challenges Faced by High Entropy Alloys

Although HEAs have garnered significant attention for their unique combination of properties, there are still a number of challenges associated with their synthesis, processing, and characterization.

One of the main challenges is the development of cost-effective and scalable synthesis techniques for these complex alloys.

Furthermore, the lack of a clear understanding of the relationship between composition, microstructure, and properties makes it difficult to accurately predict the properties of these alloys, which can limit their widespread adoption in industry.

New Research in the Field of High-Entropy Alloys

Due to their potential applications, HEAs have been the subject of intense research and development in recent years. Researchers have been working to understand the properties of HEAs and to develop new alloys with improved properties for specific applications.

One of the key areas of research in the field of HEAs is the study of structure-property relationships. Researchers are working to understand how the microstructure of HEAs affects their properties and how these properties can be tailored for specific applications.

A recent study has shown that adding small amounts of cerium to a high-entropy alloy with a high concentration of nickel and cobalt improves the high-temperature strength of the alloy.

An important research topic in the field of HEAs is the study of mechanical properties. Researchers are working to understand how the mechanical properties of HEAs are influenced by their composition, microstructure, and processing conditions.

Zhang analyzed the effects of different elements on the microstructure and mechanical properties of high entropy alloys containing nickel, cobalt, and aluminum.

Another research paper reported that the high-temperature strength of a high-entropy alloy with a high concentration of nickel, cobalt, and aluminum can be improved by changing the processing conditions used to produce the alloy.

High entropy alloys are also being studied for their corrosion resistance, and researchers are working to understand how the corrosion resistance of HEAs is influenced by their composition and microstructure.

Recently published research has shown that adding small amounts of chromium to a high-entropy alloy with a high concentration of nickel and cobalt improves the corrosion resistance of the alloy.

HEAs are also being studied for their biocompatibility, and researchers are working to understand how the biocompatibility of HEAs is influenced by their composition and microstructure.

de Oliveira has documented that HEAs with high levels of titanium and molybdenum have good biocompatibility and can be used as biomaterials for medical applications.

To Conclude

HEAs are a new and rapidly growing area of research in the field of materials science. Despite some challenges, the potential applications of HEAs are vast, and ongoing research is focused on understanding their properties and optimizing them for specific applications.

With continued research and development, the use of HEAs is expected to expand in the coming years and significantly impact a range of industries.

Continue reading: Express Test Indentation for High-Resolution Mechanical Mapping of HEAs at High Temperatures

References and Further Reading

Dada, M., Popoola, P., Adeosun, S., & Mathe, N. (2019). High Entropy Alloys for Aerospace Applications. Aerodynamics. Available at: https://doi.org/10.5772/intechopen.84982

de Oliveira, T. G., Fagundes, D. V., Capellato, P., Sachs, D., & da Silva, A. A. (2022). A Review of Biomaterials Based on High-Entropy Alloys. Metals, 12. Available at: https://doi.org/10.3390/met12111940

Du, X., Ma, X., Ding, X., Zhang, W., & He, Y. (2022). Enhanced high-temperature oxidation resistance of low-cost Fe–Cr–Ni medium entropy alloy by Ce-adulterated. Journal of Materials Research and Technology, 16, 1466-1477. Available at: https://doi.org/10.1016/j.jmrt.2021.12.087

Miracle, D., & Senkov, O. (2017). A critical review of high entropy alloys and related concepts. Acta Materialia, 122, 448-511. Available at: https://doi.org/10.1016/j.actamat.2016.08.081

Wu, M., Yuan, J., Diao, G., & Li, D. (2022). Achieving a Combination of Higher Strength and Higher Ductility for Enhanced Wear Resistance of AlCrFeNiTi0.5 High-Entropy Alloy by Mo Addition. Metals, 12(11). Available at: https://doi.org/10.3390/met12111910

Zhang, J., Xin, S., Zhang, Y., Guo, P., Sun, H., Li, T., & Qin, C. (2023). Effects of Elements on the Microstructure and Mechanical Properties of AlCoCrFeNiTi High-Entropy Alloys. Metals, 13. Available at: https://doi.org/10.3390/met13010178

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Shaheer Rehan

Written by

Shaheer Rehan

Shaheer is a graduate of Aerospace Engineering from the Institute of Space Technology, Islamabad. He has carried out research on a wide range of subjects including Aerospace Instruments and Sensors, Computational Dynamics, Aerospace Structures and Materials, Optimization Techniques, Robotics, and Clean Energy. He has been working as a freelance consultant in Aerospace Engineering for the past year. Technical Writing has always been a strong suit of Shaheer's. He has excelled at whatever he has attempted, from winning accolades on the international stage in match competitions to winning local writing competitions. Shaheer loves cars. From following Formula 1 and reading up on automotive journalism to racing in go-karts himself, his life revolves around cars. He is passionate about his sports and makes sure to always spare time for them. Squash, football, cricket, tennis, and racing are the hobbies he loves to spend his time in.

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