High Entropy Alloys: New Materials Developed from “Chemical Disorder”

Recently, the article "Liquid Metal for the Synthesis of High Entropy Alloy Nanoparticles" was published in the internationally renowned academic journal Nature, with Wuhan University as the first signing unit. Fu Lei's research team used "mixing enthalpy" as the starting point, reduced the Gibbs free energy change, and used liquid metal to achieve atomic manufacturing of various high entropy alloy systems under mild conditions, greatly expanding the component selection space of high entropy alloys, and is expected to promote their application in more key fields.

Speaking of alloys, some people may have heard of them, but as for high entropy alloys, even fewer people have heard of them. So, what are high entropy alloys?

In chemistry, entropy is a concept in thermodynamics, first proposed by German physicist Clausius. With the development of information theory and statistical physics, scientists have come to understand that the essence of entropy is actually the "internal disorder" of a system, and high entropy refers to the high disorder and disorder of the system.

To know the origin of high entropy alloys, we must first talk about alloys. Alloys are widely used in daily life, such as aluminum alloys and steel. Steel is based on iron, and adding trace amounts of non-metallic elements such as carbon will result in an alloy dominated by iron. This was known to our ancestors before the Common Era, as can be seen from bronze ware: adding a small amount of tin to copper will produce bronze; adding a small amount of magnesium and silicon to aluminum will produce an aluminum alloy. However, based on past experience, the more types of metals added to an alloy, the more likely it is that the material will become brittle. Therefore, alloys generally have only one or two components. As humans explore the world and outer space, traditional alloy materials are gradually restricted, so alloys with excellent performance under more demanding conditions are needed.

In 2004, Ye Junwei, the "Father of High Entropy Alloys", published his research results and prepared high entropy alloys, thus verifying his idea: mixing enough elements in equal proportions, the resulting mixed alloy will have too high a disorder, which may prevent the formation of clusters that cause alloy embrittlement. Since then, high entropy alloys have gradually entered the field of vision of scientists, breaking people's inherent impression of alloys.

As a new type of material developed based on "chemical disorder", high entropy alloys are made by mixing multiple components, which makes them more stable in performance. They also have superconductivity and magnetism, and are expected to be used in the fields of electricity, medical care, communications, etc.

High entropy alloys are chemically resistant to high temperature oxidation, and can be plated on the outer layer of metal to protect the metal. Currently, known high temperature oxidation resistant materials, such as nickel-based alloys, are widely used in the aerospace field, but nickel-based alloys are expensive, and high entropy alloys are called "the best alternative to the next generation of high temperature oxidation resistant materials" due to their special structure and performance.

Hydrogen is the cleanest energy source and can be obtained from the electrolysis of water. However, the cost of electrolysis is very high. The synthesis of efficient hydrogen evolution catalysts is the key to improving the production of hydrogen by water electrolysis. Transition metal high entropy alloys are expected to play a greater role in the field of hydrogen production in the future.

Although high-entropy alloys are not widely used at present, with the development of science and technology, the performance of the material will be even better, and it will become a powerful assistant in our exploration of extreme environments such as outer space.

(The first author is a professor and doctoral supervisor at Northwest Normal University, and the second author is a master's student at Northwest Normal University)