“Treasure” Metal Materials—Analysis of Top Ten Application Prospects of High Entropy Alloys and Industry Development Suggestions

With the rapid development of science and technology and the urgent demand for high-performance alloy materials in the construction of the national economy, traditional alloy materials with a single main element are gradually unable to meet people's increasing service needs. A new alloying strategy is urgently needed to break the traditional strategy. shackles. In order to solve the above problems, the concept of high-entropy alloys was proposed in 2004. High-entropy alloys have received global research and attention because of their revolutionary design concepts and special physical, chemical and mechanical properties.

High-entropy alloys can greatly expand the scope of metal material composition design and are expected to play an important role in major engineering fields such as national defense, aviation, aerospace, oceans, nuclear energy, medical care, and new energy. This article combines the specific needs for advanced high-entropy alloy materials in various fields, sorts out the characteristics and connotations of high-entropy alloy materials, analyzes the overall situation and prospects of the development of high-entropy alloy materials, and clarifies the development status of high-entropy alloys at home and abroad. On this basis, the gaps and deficiencies in the field of high-entropy alloys in my country were pointed out, and several research suggestions were put forward to address the above issues.

I. Introduction

In the history of the development of human society, the discovery and use of metal materials has greatly improved social productivity and is of milestone significance. For a long time, traditional metal materials such as steel, aluminum alloys, copper alloys, titanium alloys, and magnesium alloys have mostly been prepared with one or two metal elements, and their microstructure has been adjusted by adding a small amount of alloying elements. Meet specific performance needs. However, this alloy design strategy always limits the composition design space of alloy materials to the corners of the multivariate phase diagram, limiting the total number of element combinations and constraining the development of new alloy materials. With the rapid development of science and technology and the urgent demand for high-performance alloy materials in the construction of the national economy, traditional alloy materials with a single main element are gradually unable to meet people's increasing service needs. A new alloying strategy is urgently needed to break the traditional strategy. shackles.

In order to solve the above problems, the concept of high-entropy alloys (or multi-principal alloys) was proposed in 2004. Relevant studies have found that alloys obtained by mixing multiple elements in near/equiatomic proportions do not form complex intermetallic compounds, but form a simple solid solution structure. The emergence of high-entropy alloys breaks the traditional alloy design concept based on mixing enthalpy and opens up a broad composition design space for the development of new materials. At present, the research scope of high-entropy alloys includes material design, structure control, processing and preparation, microstructure characterization, mechanical properties, functional properties (such as magnetism, radiation resistance, catalytic properties, thermoelectric properties, etc.), plastic deformation theory, and computer simulation Simulation etc.

High-entropy alloys have received global research and attention due to their revolutionary design concepts and special physical, chemical and mechanical properties. At present, major developed countries and regions (including the United States, Europe, Canada, Australia, Japan, etc.) as well as my country are actively carrying out relevant research work and application exploration in this field. High-entropy alloys can be applied in many key fields such as national defense, aviation, and aerospace. At present, most research on high-entropy alloy materials in my country still remains at the laboratory stage, and the industrialization process is extremely slow. At present, the international situation is changing rapidly, and it is of great strategic significance to develop and promote new high-entropy alloy materials with independent intellectual property rights. To this end, on the basis of introducing the characteristics and connotation of high-entropy alloy materials, we analyze the industrial application prospects of advanced high-entropy alloys, clarify the development status of high-entropy alloys at home and abroad, point out the gaps and deficiencies in the field of high-entropy alloys in my country, and give Corresponding development strategies are aimed at promoting the upgrading and development of related industries.

2. Characteristics and connotations of high-entropy alloys

The initial definition of high-entropy alloys is: alloys containing at least 5 major elements, each element content is between 5% and 35%, and if it contains minor elements, the minor element content is less than 5%. With the continuous deepening of research on high-entropy alloys, people have gradually discovered that the above definition cannot accurately cover all the characteristics of high-entropy alloys. For example, assume that a high-entropy alloy with an equiatomic ratio is composed of 25 elements. Although its mixing entropy is as high as 3.2R, since the content of each major element is only 4%, it does not meet the original definition of a high-entropy alloy. Therefore, the definition of high-entropy alloys has been revised, that is, based on the mixing entropy in the molten state or the state of complete miscibility at high temperature as the standard, only when the mixing entropy reaches 1.5R, it is possible to form a stable solid solution phase. At this point, the mixing entropy is used as the standard to define high-entropy alloys, and it is stipulated that when the mixing entropy of the alloy is greater than 1.5R, it is called a high-entropy alloy; when the mixing entropy of the alloy is between 1 and 1.5R, it is called a high-entropy alloy. Medium-entropy alloy; when the mixing entropy of the alloy is lower than 1R, it is called a low-entropy alloy.

High-entropy alloys have only been reported for more than 10 years. Although there are still a series of controversial issues regarding the definition of "high-entropy alloys", this does not affect the popularity of high-entropy alloys due to their excellent properties and broad multi-dimensional composition space. scientific and application potential. In this sense, high-entropy alloys are actually a brand-new alloy design idea. Therefore, the article believes that the definition of high-entropy alloy can be expanded to: an alloy system composed of multiple major elements. According to this definition standard, a large number of high-entropy alloy systems already exist. There are as many as 37 elements used in high-entropy alloys, which is close to 1/2 of the 72 candidate elements in the periodic table of elements (except noble gases, halogen elements and radioactive elements).

As a multi-principal alloy material, high-entropy alloy has many unique characteristics and advantages in terms of microstructure and performance. High-entropy alloys have a "high entropy effect" in thermodynamics, which can promote the formation of high-entropy solid solutions; they have a "hysteresis diffusion effect" in dynamics, and the diffusion coefficient is significantly lower than traditional alloys; they have a "lattice distortion effect" in terms of microstructure ", which can cause solid solution strengthening to increase strength; it has a "cocktail effect" in terms of performance, which is beneficial to optimizing various properties of the alloy. In addition, in recent years, new academic discoveries have been made about the chemical short-range ordered structure and ultra-high interstitial atom solid solubility of high-entropy alloys.

In terms of mechanical properties, high-entropy alloys not only have an excellent combination of strength and plastic toughness at room temperature, but can also exhibit excellent performance in ultra-low temperature and ultra-high temperature extreme environments. High-entropy alloys also have significant advantages in elasticity, high-temperature damping properties, soft magnetism, radiation resistance, corrosion resistance, wear resistance and other properties, and have the potential to be developed as advanced structural-functional integrated materials.

There are currently two classification methods for high-entropy alloys. One category is based on the position of its main elements in the periodic table, which is divided into 3d transition group high entropy alloys, refractory high entropy alloys, rare earth high entropy alloys, noble metal high entropy alloys, non-metal element doped high entropy alloys, etc.; According to the characteristics and uses of high-entropy alloys, they are divided into lightweight high-entropy alloys, high-temperature-resistant refractory high-entropy alloys, corrosion-resistant high-entropy alloys, radiation-resistant high-entropy alloys, biomedical high-entropy alloys, and eutectic high-entropy alloys. Alloys, wear-resistant high-entropy alloys, hydrogen-storage high-entropy alloys, catalytic high-entropy alloys, soft magnetic high-entropy alloys, etc. This article will adopt the second classification method, which is to classify high-entropy alloys according to their characteristics and uses, and elaborate on their application prospects and development status one by one.

3. Application prospects of high-entropy alloys

(1) Lightweight high-entropy alloy

With the rapid changes in the automobile industry and the further increase in lightweight requirements for energy conservation and emission reduction, the demand and development of lightweight alloy structural components have also undergone great changes. Lightweight high-entropy alloys can take advantage of their light weight and high strength and can be used to replace structural panels, seat frames, gearbox hubs and other components in automobiles. They can effectively reduce the weight of automobiles, save oil consumption in traditional automobiles, and improve the efficiency of new energy automobiles. Battery life. The automobile industry uses a large number of lightweight structural components. my country's annual automobile aluminum consumption exceeds 5×106t. Together with peripheral supporting and downstream parts manufacturers, the output value of the related industrial chain exceeds 100 billion yuan. In addition, high-performance lightweight metal materials can also be used as an important component of aerospace structural materials. At present, titanium alloys have been widely used in the fields of aviation, aerospace and weapons and equipment. my country's demand for titanium alloys is increasing at a rate of 20% to 30% per year. The main problem with traditional titanium alloys is their limited use temperature. Lightweight high-entropy alloys are expected to break through this limitation due to the addition of a large amount of refractory elements. As the flight Mach number of aerospace vehicles continues to increase, the requirements for weight reduction are getting higher and higher. The use of lightweight alloys is imperative, and lightweight high-entropy alloys are expected to meet this demand with their excellent comprehensive mechanical properties. .

(2) High temperature resistant refractory high entropy alloy

Current nickel-based superalloys are limited by their melting points, and their yield strength drops sharply in a temperature range greater than 1000°C. High-temperature resistant refractory high-entropy alloys still have excellent high-temperature mechanical properties in the temperature range above 1000°C. They are expected to fill the gap of nickel-based high-temperature alloys in the ultra-high temperature field and become the next generation aero-engine turbine blade materials. At present, since most high-temperature-resistant refractory high-entropy alloys are non-standard products, and product types change with changes in downstream demand, the supply chain of high-temperature-resistant refractory high-entropy alloys is relatively short and belongs to a technology-centered field with production The process is complex, R&D funds are consumed, development time is long, and industry barriers are high. Equipment updates and localization in the aviation and aerospace fields have provided major potential market demand for high-temperature-resistant refractory high-entropy alloys, making high-temperature-resistant refractory high-entropy alloys a potential candidate material for aerospace engines. In the next 20 years, if the mass proportion of high-temperature-resistant refractory high-entropy alloys in aerospace engines accounts for 50%, the potential market size of high-temperature-resistant refractory high-entropy alloys required for my country's civil aviation aircraft will reach 200 billion yuan.

(3) Corrosion-resistant high-entropy alloys

Compared with traditional corrosion-resistant materials such as stainless steel, copper alloy, aluminum alloy, titanium alloy, etc., high-entropy alloys have the advantages of high strength and toughness, high wear resistance, strong magnetism, etc., and have stronger comprehensive properties. This opens up a broad space for the application of corrosion-resistant high-entropy alloys, which are expected to become structural-functional integrated materials. Compared with land resources, the development of marine resources is far from sufficient. my country has a long coastline, numerous islands, and a vast territorial sea area, which provides an important guarantee for my country's economic development, energy reserves, and resource utilization. Corrosion-resistant high-entropy alloys can be used as main materials for marine engineering and marine equipment in shipbuilding, offshore platform construction and other directions. For example, eutectic high-entropy alloys can be used in ship propellers, high-strength corrosion-resistant high-entropy alloys can be used as materials for special parts of ships, and corrosion-resistant soft magnetic high-entropy alloys can be used as magnetic materials in offshore wind power equipment. Entropy alloy coating can be applied to ship hulls. At the same time, the development of industry has increasingly higher requirements for corrosion-resistant materials. For example, materials in the petrochemical, aviation, and aerospace fields need to be exposed to extreme environments such as strong acid for a long time. High-strength corrosion-resistant high-entropy alloys can be used as special materials to withstand extremely high loads and Avoid corrosion damage; corrosion-resistant soft magnetic high-entropy alloys can be used as key magnetic materials in solenoid valves; high-entropy alloys with excellent corrosion resistance can also be used as pipeline materials in the petrochemical industry.

(4) Radiation-resistant high-entropy alloy

As a strategic emerging industry, my country's nuclear technology application industry has developed rapidly in recent years and is an indispensable and important field in the current national defense construction and national economic development. Nuclear reactor structural materials are the foundation and guarantee for the development of nuclear technology. However, existing structural materials cannot withstand the harsh working environment in advanced reactors. There is an urgent need to design and develop materials with good mechanical properties, high temperature performance and radiation resistance. Based on the excellent radiation resistance of high-entropy alloys, two types of high-entropy alloys for advanced nuclear reactors have been proposed, namely low neutron absorption cross-section high-entropy alloys and low-activation high-entropy alloys. Among them, low neutron absorption cross-section high-entropy alloys are expected to replace fuel cladding materials in reactors, while low-activation high-entropy alloys are expected to be used in reactor pressure vessels, first wall materials, cladding materials, etc.

(5) Biomedical high-entropy alloys

Biomedical metals are mostly used to manufacture various medical devices and surgical tools in orthopedics, dentistry, interventional stents and other medical fields. In 2021, my country's high-value medical consumables market will exceed 100 billion yuan, of which the orthopedic implant market will reach 34 billion yuan, a year-on-year increase of 14%. Therefore, improving the performance of existing medical metal materials and developing new medical metal materials are of great practical significance to further improve the performance level of metal medical devices and expand their medical functions, improve the market competitiveness of related products, and benefit the majority of patients. Biomedical high-entropy alloys have the advantages of high strength, high hardness, high wear and corrosion resistance, low elastic modulus, and good biocompatibility. They can be used in orthopedic implants, vascular intervention, etc., which is conducive to improving my country's The international competitiveness of metal medical device products. In addition, high-entropy alloys are expected to gain a place in the antibacterial alloy market due to their excellent comprehensive properties. Antibacterial high-entropy alloys can be widely used in equipment pipelines and storage tanks in kitchenware, home appliances, food industry, medical equipment, beer, dairy, pharmaceutical and other enterprises.

(6) Eutectic high-entropy alloy

At present, our country's special ships are developing in the direction of large-scale, high-speed, and quiet, which puts forward higher requirements for power systems, especially propulsion devices. The propeller is the core component of the ship's propulsion device. Its manufacturing level directly affects the overall performance of the ship. Its production capacity is an important reflection of a country's shipbuilding level. The many challenges faced by propellers during their service make traditional propeller materials such as copper alloy and stainless steel no longer able to meet the performance design requirements of the next generation of ships, seriously restricting the future development of ship equipment. The major technical needs and key scientific issues faced by the field of high-performance alloys for ship propellers need to be solved urgently. For example, the preparation technology of traditional copper alloys and stainless steel materials has reached its limit and cannot meet the requirements of lightweight, high strength and corrosion resistance for the next generation of ships. Require. Eutectic high-entropy alloys have excellent casting properties, mechanical properties and seawater corrosion resistance. They have huge industrial application potential, and related research is relatively mature. They have important application prospects and significant theoretical research value in the field of shipbuilding industry; they are also suitable for some Complex shape castings with high corrosion resistance requirements, such as some European companies have applied it to corrosion-resistant parts in the petrochemical industry.

(7) Wear-resistant high-entropy alloy

Wear-resistant materials account for a large proportion of energy consumption and economic costs in industrial fields such as building materials, thermal power generation, and metallurgical mining. At the same time, in the production process of minerals, cement, coal powder and other technological fields, machinery and equipment will be damaged due to wear and tear of parts. It must be replaced. Therefore, the development of new wear-resistant materials has great practical significance. The emergence of high-entropy alloys can solve the performance bottleneck problem of traditional wear-resistant materials and become an important material selection for equipment serving under harsh working conditions such as high temperature, oxidation, and corrosion. Wear-resistant high-entropy alloys are expected to be used in fields such as grinding balls, liners, crusher hammers, and track shoes.

(8) Hydrogen storage high-entropy alloy

In recent years, in order to achieve the goals of carbon neutrality and carbon peaking, hydrogen energy and related industries have received great attention. The demand for hydrogen energy has continued to grow, and the hydrogen storage material industry market has continued to develop. In 2020, the market size of my country's hydrogen storage materials industry was 762 million yuan. Among them, rare earth hydrogen storage materials are currently the only hydrogen storage materials that can achieve large-scale commercialization, with a market size of 690 million yuan, accounting for 90.55%; other hydrogen storage materials The materials market size is 72 million yuan, accounting for 9.45%. my country's abundant reserves of rare earth resources provide sufficient raw material market guarantee for the development of the hydrogen storage material industry. However, the high cost of hydrogen storage materials has become the main factor restricting its development. High-entropy alloys composed of a variety of non-precious metal elements have significant lattice distortion. Different atomic radii will produce larger void locations, and the multi-principal characteristics of high-entropy alloys increase the binding energy between the matrix and hydrogen. Therefore, , high-entropy alloy is a kind ofHydrogen storage alloys with great potential are expected to become substitutes for rare earth hydrogen storage alloys.

(9) Catalytic high-entropy alloys

Catalysis is closely related to human life. Catalysts are widely used in modern chemical industry, petroleum processing industry, energy, pharmaceutical industry and environmental protection fields. With the elimination of backward production capacity, the capacity utilization rate of my country's chemical catalyst industry has gradually increased. Although traditional precious metal catalytic materials have good catalytic activity and high stability, they are costly and resource scarce; traditional transition metal catalysts have low catalytic activity and are easily Problems such as oxidation and difficulty in storage. Compared with the above-mentioned traditional catalysts, high-entropy alloy catalytic materials have the characteristics of low overpotential, strong thermal stability, fast kinetics and low cost, and have potential significant application value in the fields of fuel, chemical industry, medicine, energy and other fields.

(10) Soft magnetic high entropy alloy

Soft magnetic materials are key components in the intelligent era and are mainly used in power grids, photovoltaics, energy storage, new energy vehicles and charging piles, fifth-generation mobile communication technology (5G), wireless charging, variable frequency air conditioners, rail transit, green lighting, etc. fields; it has broad application prospects in new infrastructure construction fields such as high-end consumer and industrial electronics, cloud computing, and the Internet of Things, with high frequency, high power, and miniaturization as important development directions. In recent years, the rapid development of the new energy field has opened up demand for the application of soft magnetic alloys. Global magnetic material manufacturers are mainly concentrated in Japan and China, of which my country's output accounts for about 70% of the world's output. According to statistics from the Magnetic Materials Industry Association, in 2020, my country's magnetic materials industry produced and sold approximately 1.3×106t of magnetic materials, of which 2.9×105t were soft magnetic materials; it is expected that by 2025, the production and sales of soft magnetic materials will reach 4.89 ×105t, the market size is 15.077 billion yuan.

Although traditional soft magnetic materials have excellent soft magnetic properties, they still do not fully meet the needs in terms of corrosion resistance, wear resistance, strong plasticity and high temperature oxidation resistance. Due to its wider composition design range and flexible microstructure, high-entropy alloys can make the material have excellent soft magnetic properties while also having a variety of properties in corrosion resistance, mechanical properties and high-temperature oxidation resistance, meeting extreme needs. Use under complex conditions. High-entropy alloys have great application prospects under conditions of high frequency, low loss, corrosion, friction, high temperature and high load.

5. Development status of high-entropy alloys

(1) Lightweight high-entropy alloy

With its advantages of high specific strength and high specific hardness, lightweight high-entropy alloys have application potential in aviation, aerospace, energy, transportation and other fields, and have been widely studied by many scholars. The lightweight high-entropy alloys currently developed are divided into the following two categories based on density: one is an ultra-low-density lightweight alloy composed of light elements such as Al, Be, Li, Mg, Sc, Si, Zn, Ti, etc.; One type is a low-density, lightweight high-entropy alloy composed of elements such as Ti, Zr, V, Nb, Al, Cr, etc. Ultra-low density lightweight high-entropy alloy refers to a high-entropy alloy with a density between aluminum alloy and titanium alloy. The element composition is usually dominated by Al element. Low-density lightweight high-entropy alloy generally refers to a density between titanium alloy and steel. High entropy alloy. This type of alloy usually uses Ti as the main element and exhibits better comprehensive mechanical properties than ultra-low density, lightweight high-entropy alloys.

Although lightweight high-entropy alloys have many excellent properties such as low density, high strength, and high hardness, current research mainly focuses on room temperature quasi-static mechanical properties. In the future, its research scope should be further expanded, such as the dynamic mechanical properties, high temperature mechanical properties, fracture toughness, etc. of lightweight high-entropy alloys. In addition, most lightweight high-entropy alloys currently suffer from room temperature brittleness. How to obtain lightweight high-entropy alloys with tensile plasticity through composition design in the future is a difficult problem that scientific researchers need to overcome.

(2) High temperature resistant refractory high entropy alloy

High-temperature-resistant refractory high-entropy alloys are mainly composed of high-melting-point refractory elements such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W from groups IVB, VB, and VIB in the periodic table of elements. Sometimes Al is also added , Si, Co, Ni, O, N and other non-refractory elements regulate the microstructure and comprehensive properties of the alloy. The biggest feature of high-temperature resistant refractory high-entropy alloys is their excellent high-temperature yield strength and high-temperature phase stability.

High-temperature resistant refractory high-entropy alloys have shown great potential as high-temperature structural materials, but their severe room temperature brittleness limits the industrial application of the materials. For example, the first-generation refractory high-entropy alloys (NbMoTaW and VNbMoTaW alloys) developed in the United States only have a compressive strain rate of about 2% at room temperature, and the fracture morphology shows typical brittle cleavage fracture characteristics. Currently, only the TiZrHfNbTa series and its derived refractory high-entropy alloys can have a certain elongation under quasi-static stretching conditions, but they are still far from meeting the huge demands for safety and processability of advanced engineering materials. Therefore, how to effectively improve its room temperature plasticity is the primary goal for the future development of refractory high-entropy alloys. In addition, as a potential high-temperature alloy, the poor oxidation resistance of high-temperature-resistant refractory high-entropy alloys is also a bottleneck that limits its further development. Most refractory elements cannot form an effective protective layer during the oxidation process. Therefore, anti-oxidation elements such as Al and Cr can be added to refractory high-entropy alloys to form a dense oxide layer and improve the anti-oxidation properties of the alloy. Currently, there is no refractory high-entropy alloy brand with both excellent mechanical properties and oxidation resistance. How to control the microstructure and properties of refractory high-entropy alloys through composition/process is an urgent problem that needs to be solved in this field in the future.

(3) Corrosion-resistant high-entropy alloys

Under certain circumstances, materials will be tested by acid, alkali, seawater and other environments in practical applications. These harsh service environments will cause great damage to the material itself, thereby reducing the service life of the material and causing safety hazards. Therefore, the research on corrosion-resistant high-entropy alloys is a crucial topic. Current research shows that high-entropy alloys have better comprehensive corrosion resistance than traditional corrosion-resistant materials (such as stainless steel, copper alloys, aluminum alloys, etc.) and are expected to be used as corrosion-resistant materials serving in extreme environments in the future.

The advantage of corrosion-resistant high-entropy alloys is that they not only have excellent corrosion resistance, but can also meet the material requirements for engineering applications in terms of structural mechanics and other functional applications. my country has currently designed a corrosion-resistant soft magnetic high-entropy alloy (Fe2.25Co1.25Cr) 94Al6 with a single-phase BCC structure. This alloy not only exhibits excellent soft magnetic properties, but also has excellent corrosion resistance. Its advantages The corrosion potential is twice that of traditional 304 stainless steel. It can effectively protect the material itself from seawater erosion and damage in seawater environments, effectively solving the problem of using magnetic materials in corrosive environments.

The "cocktail effect" brought about by the vast element adjustment space of high-entropy alloys provides a way to design high corrosion resistance. Our country has designed a face-centered cubic (FCC) high-entropy alloy with excellent mechanical properties and corrosion resistance. The alloy has a tensile strength of more than 600 MPa and a fracture plasticity of 70%; in a 0.1 mol/L H2SO4 solution In the environment, multiple elements work synergistically to form a dense passivation film, which exhibits corrosion resistance far superior to that of 316L stainless steel, achieving structural and functional integration of mechanical properties and corrosion resistance. Multiphase structures also have good corrosion resistance, such as a corrosion-resistant eutectic high-entropy alloy composed of FeCrNiCoNb0.5. The alloy has an ultra-fine eutectic structure of nanoscale size, which can form a stable passivation film during the corrosion process; at the same time, the passivation film of the alloy has self-healing ability and shows good resistance in 1mol/L NaCl solution. Corrosion performance, its passivation film width is 3 times that of 304 stainless steel, and its corrosion resistance is better than traditional corrosion-resistant materials such as stainless steel, aluminum alloy, titanium alloy, and nickel alloy.

High-entropy alloy corrosion-resistant coatings have also received widespread attention. Chinese researchers used laser cladding technology to prepare a FeCoCrAlNi high-entropy alloy coating on the surface of 304 stainless steel substrate. The hardness of the coating is three times that of the original substrate alloy. Corrosion test results in 3.5wt.% NaCl solution show that FeCoCrAlNi high-entropy alloy coating can effectively improve the corrosion resistance and pitting corrosion resistance of the alloy. The application of coating technology provides a new direction for the development of corrosion-resistant high-entropy alloys. Therefore, corrosion-resistant high-entropy alloy coating materials show broad application prospects.

(4) Biomedical high-entropy alloys

High-entropy alloys can select specific alloying elements according to biomedical needs, thereby giving them special biomedical functional properties. In addition, the high entropy effect and lattice distortion effect also give biomedical high entropy alloys good strength, hardness, corrosion resistance, wear resistance, biocompatibility and antibacterial properties. At present, there has been some research on biomedical high-entropy alloys. According to different functions, biomedical high-entropy alloys can be divided into two categories: implantable high-entropy alloys and antibacterial high-entropy alloys.

Although a lot of research work has been done on biomedical high-entropy alloys and some groundbreaking research results have been achieved, there are still the following problems to be solved: The designed biomedical high-entropy alloys are mainly cast, and subsequent thermal processing should be further carried out Processing to ensure homogenization of its tissue components; research on the performance of biomedical high-entropy alloys is not yet comprehensive, and a full range of biological evaluations should be conducted in the future based on specific needs.

(5) Radiation-resistant high-entropy alloy

High-entropy alloys have become competitive candidate materials for key components of nuclear reactors due to their outstanding mechanical properties, high-temperature properties, and radiation resistance. It has broad application prospects in the fields of fuel cladding materials, reactor pressure vessels, first wall materials, and reactor pipe materials. Currently, many well-known scientific research institutions at home and abroad are conducting research on radiation-resistant high-entropy alloys. High-entropy alloys have better radiation resistance than traditional alloys. Studies have found that adding interstitial elements to high-entropy alloys can enhance the chemical short-range ordering of high-entropy alloys, thereby improving their radiation resistance. CoCrFeNiMn high-entropy alloys have stronger resistance to helium bubble growth than pure metallic nickel, and as the number of principal elements increases, the size of helium bubbles gradually decreases.

 

Although research on the irradiation properties of high-entropy alloys has shown good industrial application prospects in the field of nuclear reactors, this research is still in its infancy, and research on special high-entropy alloys under different working environments in reactors is still very limited; at the same time, , there are still many theoretical problems that need to be solved in the field of radiation-resistant high-entropy alloys. For example, high-entropy alloys such as TiVNbTa have serious element segregation after irradiation. All in all, the current database on the irradiation behavior of high-entropy alloys is relatively scarce and cannot yet provide a reliable basis for the design of reactor structural materials.

(6) Eutectic high-entropy alloy

Dalian University of Technology first proposed using the concept of eutectic alloys to design high-entropy alloys in order to obtain a high-entropy alloy composed of a two-phase eutectic structure, thereby obtaining a eutectic high-entropy alloy with good casting performance and excellent comprehensive mechanical properties. AlCoCrFeNi2.1 eutectic high-entropy alloy exhibits uniform and fine lamellar morphology in the cast state, with a tensile strength exceeding 1GPa and a plasticity as high as 17%. This high strength and high plasticity obtained in the cast state makes it a One of the most valuable high-entropy alloys for industrial applications. Subsequently, many eutectic high-entropy alloys with excellent mechanical properties and special functions were developed and reported. The most widely studied are the AlCoCrFeNi system and CoCrFeNi-M (M=Nb, Ta, Zr, Hf, Mo, etc.) alloy system.

Eutectic high-entropy alloys of the AlCoCrFeNi system are usually composed of a softer FCC phase and a harder B2 phase. The interaction between the soft and hard phases during the deformation process allows this type of alloy to exhibit excellent comprehensive mechanical properties. In order to further improve the strong plasticity of this type of eutectic high-entropy alloy, researchers have performed different processing heat treatments and different preparation methods on this type of alloy to optimize the alloy. For example, after rolling and heat treatment, the yield strength of AlCoCrFeNi2.1 alloy can be greatly increased to 1.4GPa with a small loss of plasticity, which is approximately 1.85 times higher than the yield strength of 650 MPa under as-cast conditions; in addition, Since the AlCoCrFeNi system eutectic high-entropy alloy contains more Al and Cr elements, this type of alloy usually has good corrosion resistance and oxidation resistance, which is beneficial to the application of the alloy in seawater and high-temperature environments. CoCrFeNi-M eutectic high-entropy alloys are usually composed of a soft FCC phase and a brittle and hard topologically close-packed phase. The topologically close-packed phase is a crystal structure suitable for high-temperature applications, which gives the eutectic high-entropy alloy excellent high-temperature mechanical properties. In addition to the above-mentioned structural properties, eutectic high-entropy alloys benefit from the addition of different elements, so that the alloys also show considerable application prospects in terms of functional properties, such as soft magnetic properties, giant magnetoresistance effect, etc.

Although eutectic high entropy has shown great application potential in many engineering fields, current research on this type of alloy mainly focuses on the development of components, optimization of mechanical properties, and deformation mechanisms. Due to the good casting fluidity of eutectic high-entropy alloys, more in-depth research on the preparation of engineering-sized ingots and practical engineering should be conducted.

(7) Wear-resistant high-entropy alloy

Compared with traditional alloys, high-entropy alloys have a larger composition design space and can form richer microstructure structures. Therefore, high-entropy alloys exhibit many excellent properties that are difficult to match with traditional alloys, such as high strength, high hardness, Resistant to corrosion, wear, oxidation and high temperature softening, etc. In terms of wear resistance and lubrication, the hardness of the currently reported Al0.2Co1.5CrFeNi1.5Ti high-entropy alloy is smaller than SUJ2 bearing steel and SKH51 die steel, and the wear resistance is at least 2 times that of traditional wear-resistant steel; Al0.2Co1.5FeNi1. The wear resistance of 5Ti0.55Si0.1 high-entropy alloy is better than the classic Stellite 6 wear-resistant alloy; AlCoCrFeNi-M high-entropy alloy has excellent corrosion resistance and wear resistance in 90% H2O2 solution, and has engineering applications potential. Based on the concept of high-entropy alloys, our country has created a series of high-entropy alloy-based high-temperature self-lubricating materials, such as CoCrFeNi-Gr-MoS2 and CoCrFeNi-Ag-BaF2/CaF2. The high-entropy alloy matrix ensures good mechanical properties of the composite material, and the lubrication The synergistic effect of phases and oxidation products enables continuous lubrication from room temperature to high temperature.

Although wear-resistant high-entropy alloys have shown great theoretical research value, there are still many theoretical issues in this field that have not yet been clarified. For example, there is still a lack of relevant reports on the effects of pairing and temperature on the friction and wear behavior of high-entropy alloys. More importantly, the performance database on the wear behavior of high-entropy alloys is relatively scarce and cannot provide a reliable basis for the design of wear-resistant materials.

(8) Catalytic high-entropy alloys

High-entropy alloys, due to their wide range of elemental compositions and inherently complex surfaces, can provide a large number of binding sites and can obtain a nearly continuous distribution of adsorption energy curves. The United States reported a high-entropy phosphate catalyst material in the form of highly uniform spherical particles, which has superior catalytic activity in the oxygen evolution reaction that is much higher than that of traditional catalysts. Researchers from India prepared nanocrystalline equiatomic AuAgPtPdCu high-entropy catalysts with high catalytic activity in reduction reactions, completing 100% conversion of CO2 to gas products at low voltage (-0.3V).% conversion. Although many elements are present in the catalyst, the electrocatalytic activity is mainly described by the presence of redox-active copper metal, while other metals only provide synergistic effects. High-entropy alloy catalysts also have broad application potential in oxygen reduction, water electrolysis, ammonia oxidation and other reactions. Compared with traditional catalysts, high-entropy catalysts have the characteristics of low overpotential, strong thermal stability, and fast kinetics, which make them have potential application value in the fields of fuel cell production, chemical raw material preparation, and new energy power generation. In terms of photothermal conversion, a high-entropy alloy nanoparticle composed of 21 elements was synthesized using arc discharge plasma, which showed efficient photothermal conversion performance.

(9) Hydrogen storage high-entropy alloy

High-entropy alloys will produce larger void locations due to their significant lattice distortion and different atomic radii. Moreover, the multi-principal characteristics of high-entropy alloys increase the binding energy between the matrix and hydrogen, which is beneficial to improving hydrogen storage performance. Early research on the hydrogen storage properties of high-entropy alloys mainly focused on hydrogen storage capabilities. Subsequently, the absorption/desorption cycle characteristics of high-entropy alloys have received widespread attention. Our country has reported the preparation of TiZrFeMnCrV alloy through arc melting and mechanical grinding. The alloy has ultra-fast hydrogen absorption kinetics, and the hydrogen absorption capacity at 30°C can reach 1.80wt.%; at the same time, the alloy has excellent adsorption/desorption properties. Cycle performance: the capacity remains stable at 1.76 wt.% after 50 cycles, showing good reversible hydrogen storage performance. As a new type of hydrogen storage alloy that does not contain rare earth metals, high-entropy alloys can be used as candidate materials in new energy vehicles, energy power generation and other fields.

(10) Soft magnetic high entropy alloy

Soft magnetic materials are magnetic materials with low coercivity and high magnetic permeability. They are easy to magnetize and demagnetize. Their main function is to convert and transmit electromagnetic energy and are widely used in various power conversion equipment. The design concept of high-entropy alloy multi-principal alloy significantly broadens the composition design range of materials. It can contain multiple magnetic and non-magnetic elements at the same time. The interaction between each element can produce unexpected effects. For this reason, it can be The material's magnetism, corrosion resistance, mechanical properties and high-temperature oxidation resistance are adjusted within a wide range, so that the material has higher comprehensive performance to meet the needs of use under extremely complex conditions. For example, Chinese researchers designed and prepared a super-tough soft magnetic high-entropy elemental alloy Fe32.6Ni27.7Co27.7Ta5.0Al7.0 enhanced by coherently ordered nanoprecipitates. The alloy's saturation magnetization, coercivity, and Curie The temperature, resistivity, yield strength, tensile strength and elongation at break are 100.2A·m2·kg-1, 78A/m, 693.8K, 103μΩ·cm, 904MPa, 1336MPa and 54% respectively. This excellent comprehensive performance It is unprecedented and shows the broad industrial application prospects of soft magnetic high-entropy alloys under high mechanical loads.

5. Shortcomings and development suggestions in the field of high-entropy alloys in my country

(1) Shortcomings in the field of high-entropy alloys in my country

1. my country relies on imports of high-purity raw materials for high-entropy alloys, threatening the security of the industrial chain.

There are 9 kinds of high-purity raw materials in short supply in our country: U, Fe, Mn, Al, Sn, Pb, Ni, Sb, Au; there are 8 kinds of high-purity raw materials in severe shortage: Cr, Cu, Zn, Co, Sr, K, B and Pt group elements, etc. The reserves of such raw materials are low and new production is insufficient, which creates a huge gap with the rapidly growing market demand, resulting in an increase in the cost of using high-entropy alloys and limiting their further development. Taking Co as an example, the total global resources are about 7.6×106 t. However, the resources are extremely unevenly distributed and are mainly distributed in countries and regions such as the Democratic Republic of the Congo and Australia. my country accounts for only 1% and relies heavily on imports. Co is one of the most commonly used elements in high-entropy alloys. The severe shortage of high-purity raw materials in China will threaten the security of related industrial chains.

2. Domestic enterprises do not pay enough attention to it, and the cooperation between "industry, academia, research and application" is not close.

Chinese companies do not pay enough attention to high-entropy alloy materials and have not kept up with the relevant research and development progress of foreign companies. Enterprises and research institutions lack a sound scientific research cooperation system, the enterprise-led R&D mechanism still needs to be further improved, and the "industry-university-research-application" cooperation is not close. Relevant scientific research units have small R&D investment funds, imperfect talent team construction, lack of incentive policies and R&D platforms, and lack of motivation for scientific and technological personnel to innovate. In addition, due to the lack of an "industry-university-research-application" cooperation platform for original innovation and basic research, a large number of innovative results only stay in the laboratory research stage, and there is a lack of efficient R&D platforms to verify and pilot-scale basic research results to promote scientific research. Rapid transformation and industrial application of results.

3. Insufficient theoretical simulation capabilities

There are many types of elements that can be selected for high-entropy alloys, so the number of high-entropy alloy systems is also very large. For this reason, screening high-entropy alloy components through simulation is an important research direction. However, China does not pay enough attention to the construction of high-entropy alloy databases. For example, the thermodynamic databases and phase diagram calculation software used in the development of new high-entropy alloys are mostly from the United States, Sweden and other countries, which to a certain extent makes the development of high-entropy alloy materials difficult. Research and development is controlled by others. my country still lacks effective simulation computing capabilities in the field of high-entropy alloys, making it difficult to accurately predict their structures and properties. The theoretical database construction and simulation capabilities of high-entropy alloys need to be further improved.

4. The application and evaluation system of high-entropy alloys needs to be improved

At present, most of the high-entropy alloys studied in China are composition exploration and performance research conducted under laboratory conditions. The engineering, popularization and application of scientific research results are slow, and the matching of emerging high-entropy alloy manufacturing technologies with national priority development goals needs to be further improved. . Although a large number of high-entropy alloy composition systems have been discovered in my country, they have not been systematically sorted out and classified. At the same time, my country is relatively lagging behind in the construction of new material performance evaluation, production technology, standards and specifications; a large number of independent intellectual property rights for high-entropy alloy systems with excellent properties are held abroad, and there are deficiencies in intellectual property rights in the field of high-entropy alloys in my country.

(2) Development suggestions

1. Strengthen the top-level design of high-entropy alloy materials and improve industrial policies

In combination with the national materials industry strategic layout and high-quality development goals, it is imperative to build an independent innovation system with enterprises as the main body and promote the resource integration and planning layout of the national key laboratory in the field of high-entropy alloys. Integrate with the world's high-level R&D institutions, strengthen the research and development of high-entropy alloy core technology, and establish independent intellectual property rights. Accelerate the industrialization of achievements in the field of high-entropy alloys and establish a connection mechanism between universities, scientific research, and industrialization. Encourage standardization institutions to provide standardization consulting and support services to national scientific research and industrialization projects, covering the entire chain of project establishment, implementation, promotion and application, and pilot demonstration. Encourage key enterprises to drive innovative enterprises, increase investment in research and development, make up for technological shortcomings, and actively respond to competition in the international market.

2. Strengthen the connection and communication between enterprises and scientific research institutions

Relying on experts and scholars from domestic and foreign universities and scientific research institutes to carry out consultation, we will build a healthy and green development pattern integrating R&D, production and application. Implement the innovative talent development strategy and build a sophisticated talent system for high-entropy alloy-related industries; at the same time, encourage innovative teams in this field to actively carry out international cooperation and exchanges, and provide strong economic support. Encourage enterprises to build standardized and efficient talent management systems and cultivate talent teams that are adaptable to enterprise production and highly independent and innovative. Strengthen connections with industry associations, scientific research institutions and universities, form a reserve team of elite talents corresponding to enterprises, and regularly conduct research and assessment on the research and development and application needs of high-entropy alloys at home and abroad. Strengthen the construction of a scientific research-production-consumption-re-scientific research cycle system to achieve the development goal of scientific research first, production second, complementing each other and moving forward steadily.

3. Improve high-entropy alloy material standards, testing, characterization, and evaluation systems

Establish a standard system to support the high-quality development of the high-entropy alloy industry, carry out high-entropy alloy material standard pilot actions, increase the effective supply of basic research and development of advanced metal materials, key strategic alloy materials and cutting-edge new high-entropy alloy material standards, and further exert the influence of standardization on Leading role in the development and quality transformation of the overall high-entropy alloy industry. Improve the testing, characterization, and evaluation system for new materials, establish a national high-entropy alloy testing and evaluation platform, build a new high-entropy alloy material testing and evaluation system, and solve the bottlenecks and shortcomings in its testing and evaluation. Vigorously develop independent certification and brand testing capabilities to continuously enhance international competitiveness.

4. Promote talent team building

Implement the innovative talent development strategy, strengthen the training of young and middle-aged innovative talents and teams, adopt flexible policies such as flexible introduction, establish a national high-entropy alloy collaborative innovation center, cultivate a team of independent innovative talents, cultivate a group of disciplines, professional and technical leaders, and effectively improve The activity and promoting role of talent elements in industrial technological innovation can enhance independent innovation capabilities and realize the rapid industrial application of high-entropy alloy materials.

5. Reduce material costs and create high value-added products

The current industrialization progress of high-entropy alloys is slow, mainly due to the high raw material costs and production costs. In the future, policies should encourage scientific research institutions and related enterprises to carry out scientific research and development, product innovation and brand building, further improve the scientific and technological innovation capabilities and levels of employees, strive to create high value-added products, and promote the integration of products into the global high-end manufacturing supply chain. It is recommended that through "industry-university-research-application" cooperation, we should start from the aspect of reducing the production cost of materials, create low-cost high-entropy alloy grades, optimize the variety structure, and improve international competitiveness. We should actively expand the application fields of high-entropy alloys, and promote more breakthroughs in practical applications of high-entropy alloys by carrying out cooperative research and development and demonstration application projects.

Stardust Technology (Guangdong) Co., Ltd. uses radio frequency plasma powdering equipment to specialize in R&D, production and sales of high-end metal powders and rare refractory metal powder compound materials. Welcome to contact: Manager Zheng 13318326187 (same number for WeChat and WhatsApp), we will serve you wholeheartedly.

Article reprinted from: Journal of the Chinese Academy of Engineering