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The Wonderful World of Mixed Metals: Why do high-entropy alloys exhibit unparalleled properties?
High-entropy alloys (HEAs) are a revolution in materials science in recent years. Unlike traditional metal alloys, these alloys are formed by mixing five or more elements together in relatively equal proportions. Traditional metal alloys usually contain only one or two major components, and small amounts of other elements. For example, carbon or manganese are added to iron alloys to improve their properties, but the proportions of these elements are often relatively low. Therefore, the emergence of high-entropy alloys can be described as a new material exploration.
"The definition of high-entropy alloys comes from the increase in entropy due to the increase in the number of elements during the mixing process. This increase in entropy is more obvious when the composition ratio is similar."
This term was first proposed by Taiwanese scientist Ye Jianwei. He proposed a method for actually synthesizing high-entropy alloys in 1995 and conducted research for many years thereafter. At that time, his research was almost an independent exploration on a global scale, while other countries were relatively lagging behind in research on high-entropy alloys. By the 2010s, with the advancement of technology and the emergence of application potential, countries began to increase research on high-entropy alloys.
Characteristics and applications of high-entropy alloys
Research shows that some high-entropy alloys surpass traditional alloys in terms of strength-to-weight ratio, fracture resistance, tensile strength, and resistance to corrosion and oxidation. From an application perspective, the practical application potential of high-entropy alloys in racing, aerospace, submarines and nuclear power reactors is eye-catching. The possible applications of high-entropy alloys are almost all-encompassing, and they may become key materials in aerospace, military, medical and other fields in the future.
"Whether it is the stability of solid electrets or the durability of high-strength alloys, the potential of high-entropy alloys is full of challenges and opportunities in the future."
Core effect of high-entropy alloys
The four core effects of high-entropy alloys include high-entropy effect, severe lattice distortion effect, slow diffusion effect and cocktail effect. These characteristics make high-entropy alloys very different from traditional alloys in terms of microstructure and mechanical properties.
High entropy effect
The high entropy effect is considered to be one of the most important characteristics of high entropy alloys. It promotes the formation of solid solution and simplifies the microstructure of the alloy. According to the second law of thermodynamics, solid solutions usually containing multiple elements are more likely to form a stable equilibrium state due to their high entropy value.
Severe lattice distortion effect
Multiple principal components in high-entropy alloys produce stronger lattice strains and stresses in the crystal structure. This severe lattice distortion affects the material's mechanical, thermal, electrical and chemical properties, advantages that conventional alloys cannot offer.
Slow diffusion effect
Because the structure of high-entropy alloys is macroscopically uniform and the diffusion paths required by the atoms are more complex, it exhibits lower diffusion rates, making it more resistant to changes in thermal and functional stability.
Cocktail Effect
The cocktail effect means that the improvement of alloy properties comes from the interaction of at least five major elements. The characteristics of HEAs come not only from the physical properties of single elements, but also from the interactions and combination effects between their composite phases.
Alloy design and phase formation
Different from traditional alloy designs, high-entropy alloys focus on the application of equal proportions of multiple components. Traditionally, the choice of one dominant element may have limited the performance of the alloy. High-entropy alloys are extremely flexible and versatile in this regard, and new types of alloys can be designed according to needs.
During the phase formation process of alloys, Gibbs phase law provides a basis for determining the phase number limit. However, in practice, many high-entropy alloys mainly form a single solid solution phase, which is beyond the common expectations for multicomponent systems. This phenomenon extracts the huge potential of high-entropy alloys, which are key to their ability to achieve superior properties in a variety of composition combinations.
The research on high-entropy alloys not only pushes the boundaries of materials science, but also stimulates the demand and application of new materials in all walks of life. Does this mean that we are about to enter a new era of metal material revolution?
