High Entropy Alloys

Light-weight High-entropy Alloy: a Review Article

JIA Yuefei, WANG Gang, JIA Yandong, WU Shiwei, MU Yongkun, XU Long, ZHANG Liangbo, XU Liming

Materials Reports 2020,34(17 ):17003 -17017. DOI:10.11896/cldb.20040207

Abstract （2225）

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Save High-entropy alloy has attracted masses of attention due to its unique alloy design concept and excellent properties. The previous high-entropy alloys, whose density is relatively high, are mainly based on transition group elements, refractory elements or rare earth elements, which greatly limits their application. With the trend of material lightweight, the research on light-weight high-entropy alloys are gradually increasing. Light-weight high-entropy alloy is a new branch of high-entropy alloy based on light elements such as Al, Li, Mg, Ti, etc. Light-weight high-entropy alloys have unique advantages of low density, low modulus, high specific strength and high specific hardness. In addition, light-weight high-entropy alloys also have high strength, high hardness, excellent wear resistance, good oxidation resistance, excellent corrosion resistance, good high temperature oxidation resistance, high temperature softening resistance and good biocompatibility. The superior properties of light-weight high-entropy alloys have significant potential to be applied to aerospace and biotechnology.
At present, the research of light-weight high-entropy alloys mainly involve the development of composition, preparation, characterization and properties. The development and design of new components mainly use the method of combination of empirical parameters, CALPHAD and DFT (Density functional theory) calculation. The main methods of alloys preparation are induction melting, arc melting and mechanical alloying. The phase composition and structure of light-weight high-entropy alloys usually include amorphous structure, single-phase polycrystalline structure, multiphase complex structure, etc. The research of performance mainly involves mechanical properties, include strength, hardness, high tempe-rature creep, etc., and also includes oxidation resistance, corrosion resistance, biocompatibility, etc. In this paper, the composition design, pre-paration, microstructure and properties of light-weight high-entropy alloy are reviewed. Meanwhile, the problems and challenges for light-weight high-entropy alloy are prospected.

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Research Progress on Eutectic High Entropy Alloys Article

HUANG Sirui, WU Hao, ZHU Heguo

Materials Reports 2020,34(17 ):17077 -17081. DOI:10.11896/cldb.19110176

Abstract （2026）

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Save As the earliest alloy in human history, the invention of bronze opened a new chapter in the history of metal smelting. There are more than 30 practical alloy systems that have been used for industrial sectors so far. Eutectic alloys, such as steel (Fe-C), Al-Si alloy, Ag-Cu alloy, have been widely used because of special properties such as low melting point and good fluidity.
High entropy alloys are known as one of the three major breakthroughs in alloying theory in recent decades. Theoretically, more than 7 000 high entropy alloy systems can be designed from 13 kinds of arbitrarily selected common elements. Compared with traditional alloys that based on one element, the design space of high entropy alloys are much larger. Moreover, it is found that high entropy alloys can form simple microstructures such as a simple face-centered cubic, single body-centered cubic or face-centered cubic and body-centered cubic while conventional alloys gene-rally form complex intermetallic compounds. Hence, high entropy alloys owe high strength, high wear resistance, high corrosion resistance and other excellent properties. Specific performance changes can be achieved by controlling the composition of high entropy alloys to meet different design needs, so high entropy alloys have great research value and application space.
Eutectic high entropy alloys (EHEAs) have composition characteristics of eutectic alloys and high entropy alloys. EHEAs have gained extensive attention in recent years because of the super strength, plasticity, resistance to friction and corrosion. So far, a variety of new eutectic high entropy alloys have been successfully prepared. The scholars have carried out in-depth research on the growth mechanism and strengthening mechanism of the first eutectic high entropy alloy AlCoCrFeNi_2.1 designed by Professor Yiping Lu. EHEAs have gained extensive attention in recent years because of the super strength, plasticity, resistance to friction and corrosion. In this paper, the production of eutectic EHEAs is briefly described, and the achievements are reviewed. Moreover, the composition design, preparation method and studies about EHEAs' properties are mainly introduced, and the prospects for their future development are discussed.

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Advances in Experimental Research on Irradiation Damage of High-entropy Alloys Article

JIN Ke, LU Chenyang, DOU Yankun, HE Xinfu, YANG Wen

Materials Reports 2020,34(17 ):17018 -17030. DOI:10.11896/cldb.20040078

Abstract （1699）

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Save Long before the proposal of the concept of high-entropy alloy, researchers have observed the strong dependence of ion irradiation induced swelling on the concentration of principal elements in the Fe-Cr-Ni alloy system in 1970s. Nonetheless, the underlying physics of such dependence was not systematically investigated, and principal elements were rarely targeted in design of irradiation resistant alloys, until the recent development of high-entropy alloys. This new family of alloys greatly expands the compositional space for alloy design, and provides an ideal playground of studying the impact of principal alloy elements on the irradiation response. In the recent years, significant experimental effort has been made to understand the impact of number, type, and concentration of alloying elements on the irradiation (by ions, electrons, and neutrons) induced microstructural evolution and property degradation. The up-to-date results have revealed that, defect evolution process is retarded in the alloys with high chemical complexity, through tuning the energy dissipation and the defect formation and migration energies. For example, the size of interstitial clusters is reduced, and the formation and growth of voids and helium bubbles are suppressed. It has been evidenced that proper modification of principal elements can indeed improve the irradiation resistance of alloys, however, considerable discrepancies have also been observed regarding the irradiation-induced phase instability, swelling, and hardening for different alloy systems and irradiation conditions. Therefore, a conclusive evaluation cannot be made on whether the irradiation resistance of high-entropy alloys is overall superior. We review the major progress in experimental studies on irradiation effects of high-entropy alloys, and summarize the current understanding and evaluation of the irradiation resistance. The limitations or contradictions of experimental results are discussed, and perspectives are provided for the future studies in this field.

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Review and Perspective on High Entropy Alloys Prepared by Additive Manufacturing Article

MA Minyu, LIAN Yong, ZHANG Jin

Materials Reports 2020,34(17 ):17082 -17088. DOI:10.11896/cldb.20030074

Abstract （1333）

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Computer Simulation of Irradiation Performance of High Entropy Alloy Article

XU Biao, FU Shangchao, ZHAO Shijun, HE Xinfu

Materials Reports 2020,34(17 ):17031 -17040. DOI:10.11896/cldb.20040054

Abstract （1275）

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Save Nuclear power plays a vital role in the existing energy system and is an essential part of the clean energy that is urgently needed in the world today. Nuclear structural materials are one of the most critical factors to ensure the reliability and safety of nuclear power systems. In the future fourth-generation fission and fusion reactors, the core structural materials will be in harsh environments such as high temperature, strong chemical corrosion, and intense neutron irradiation. This extremely harsh application environment puts stringent requirements on the structural materials used for future reactors. High energy neutrons generated by nuclear fission or nuclear fusion would cause significant atomic displacement in the material and produce point defects or defect clusters, which will degrade the performance of the material. Therefore, it is crucial to study the damage mechanism of materials under irradiation conditions and to develop new irradiation-resistant structural materials for the implementation of advanced reactors. In recent years, as a new type of alloys, high entropy alloy (HEAs) has shown good irradiation resistance and corrosion resistance, hence they have become one of the prominent candidates for the structural materials used in the future reactors. Among various efforts to study the irradiation damage mechanism of HEAs, computational simulation has become an extraordinary method to understand their radiation resistance, since experiments would be limited by the cost and availability of the equipment.
At present, there still exist many problems in the simulation of the irradiation performance of HEAs. One of the most important factor is that the disordered state caused by the random arrangement of elements poses a significant challenge to computational simulation methods. For example, due to the random arrangement of elements, it is difficult to define the chemical potential of each constituent element, which leads to different results in the calculation of defect energies in HEAs. Due to the large number of constituent elements, the empirical potentials for HEAs are difficult to obtain, which makes it challenging to carry out molecular dynamics simulation and other simulation methods. Moreover, the first-principles calculation method, which does not rely on the empirical potentials, is limited by computational capability. It can only simulate small atomic systems, but can not simulate the nature of defect clusters and the long-term diffusion of defects. These factors are the limitations in the simulation of the irradiation performance of HEAs.
Despite these limitations, in recent years, researchers have made significant progress in the simulation of the irradiation performance of HEAs. For example, the analysis of chemical disorder helps to explain the relationship between irradiation performance and the structure of HEAs. The mechanism of defect generation under irradiation conditions is well demonstrated by analyzing the initial displacement damage and the properties of the displacement threshold energy. The sluggish diffusion effect and the preferential diffusion of defects are explored by calculating the formation and migration energy of defects. Finally, the recombination of Frenkel defects and interactions among different types of defects are also studied, which elucidate the mechanism of defect evolution in HEAs.
In this paper, recent progress on computer simulation of irradiation performance of HEAs in recent years is reviewed. First, the basic properties of HEAs and several methods used for irradiation damage simulations are briefly introduced. Then, the irradiation damage mechanisms of HEAs are discussed in five aspects as follows: ⅰ. defect generation mechanism, ⅱ. the energetic properties of defects, ⅲ. defect diffusion properties, ⅳ. defect recombination properties, and ⅴ.the interactions among different defects. Finally, we provide some views on the current challenges and possible directions in the future .

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High Entropy Alloys:the New Irradiation-Resistant Candidate Materials Towards the Fusion Reactors Article

WANG Xuejiao, QIAO Junwei, WU Yucheng

Materials Reports 2020,34(17 ):17058 -17066. DOI:10.11896/cldb.20050032

Abstract （1273）

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Save With the development of nuclear fusion technology, the irradiation damages of materials has gained increasing attention as the vital issues for the restriction of the development of nuclear fusion. During the operation of fusion reactors, the materials are confronted with series of extreme operating conditions, including high temperature, the sputtering of high-density plasma, erosion, neutron irradiation, etc., which requires that the materials have fine characters such as good mechanical properties, neutron irradiation resistance, plasma sputtering resistance and corrosion resistance, etc. Lately, high entropy alloys (HEAs) have been gradually devised as a new irradiation-resistant candidate for fusion reactors materials, and the evaluation of irradiation resistance and the irradiation damage mechanism both require in-depth researches. HEAs are a new concept of alloy design, which forms high-thermostability solid solution phase by high entropy and low diffusivity of multi-component alloy itself. The characters of HEAs are distinguished from conventional alloys, including high entropy effect, high lattice distortion, sluggish diffusion effect and ‘cocktail’ effect, which lead to the high strength and hardness, corrosion resistance, high temperature softening resistance, excellent soft magnetic properties of HEAs. The present researches of irradiation damage of HEAs are mainly conducted by ion irradiation and it is focused on the evolution of dislocation loops, He bubbles and phase stability. It is found that the formation of dislocation loops and He bubbles of HEAs under ion irradiation has been suppressed evidently, which may be ascribed that the high lattice distortion acts as the traps to absorb the irradiation damages, such as vacancies and He atoms, thus relieve the irradiation damages. In addition, towards the operating condition of the fusion plants at high temperature, irradiation-resistant refractory HEAs have been gradually developed, which mainly utilize the high melting point elements as main compositions, such as V, Hf, Ta, W, etc. This paper introduces the research states and progresses of irradiation damages in HEAs, including the evolution of dislocation loops, He bubbles, the phase stability of matrix and precipitations of HEAs under ion irradiation, the irradiation behavior of HEAs under neutron irradiation, as well as the development and progress of irradiation-resistance refractory HEAs towards fusion reactors. Finally, the research directions in future are prospected so as to supply the reference for the development of irradiation-resistant HEAs towards fusion reactor.

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A Review on High-entropy Superalloys with FCC/L1₂ Structure Article

YAO Hongwei, LU Yiping, CAO Zhiqiang, WANG Tongmin, LI Tingju

Materials Reports 2020,34(17 ):17041 -17046. DOI:10.11896/cldb.20050264

Abstract （1271）

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Save Superalloys are unique high-temperature materials widely used in the aerospace and energy industry. The performance of conventional supe-ralloys has been improved by alloying and advanced manufacturing processes during the past decades. However, operating temperatures are now reaching limits posed by the melting temperatures of these materials. Since 2004, a new alloy design and development philosophy—high-entropy alloys (HEAs), or multi-principle-element alloys (MPEAs)—has attracted significant attention. The four core effects of HEAs, including high configurational entropy, sluggish diffusion, severe lattice distortion, and cock-tail effect, are mainly responsible for the various physical and mechanical properties.
To develop higher performance of HEAs, precipitation strengthening has been widely applied in HEAs and is proved to be effective in strengthening or toughening. Based on the HEA concept and the coherent microstructure of FCC/L1₂, a series of high-entropy superalloys (HESAs) has been developed with high strength and long-time microstructural stabilities at high temperatures.
However, the work about phase formation of HESAs were few, and the mechanisms of strengthening and deformation still lacked systematic research. In addition, the surface stability of materials at elevated temperature is an important indicator in engineering applications, but there were few studies. Recently, researchers have developed a series of HESAs based on the empirical phase formation rules and computer simulation methods. The effects of morphology and stability for the L1₂ precipitated phase, the lattice mismatch, etc. on high-temperature performance, such as high strength and creep property were studied. Moreover, the surface stability of some HESAs were investigated in oxidizing and corrosive environments.
The present work summarizes the research progress of HESAs. The phase formation, mechanical properties, high temperature oxidation and corrosion are briefly reviewed. Finally, the future perspective of HESAs is prospected.

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Research on Parameter Optimization and Microstructure and Properties of CoCrFeMnNi High Entropy Alloy Coating Cladded by Plasma Arc Welding Article

WEI Shiyong, PENG Wenyi, ZHAO Wenchao, KANG Yifan, CHEN Bin, BAO Rongrong, DENG Xiaohua

Materials Reports 2020,34(17 ):17052 -17057. DOI:10.11896/cldb.20040198

Abstract （865）

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Effect of Carbon on Microstructures and Mechanical Properties of Co-free Fe₄₀Mn₃₀Ni₁₀Cr₁₀Al₁₀ High-entropy Alloy Article

BAI Li, WANG Yuzhe, LYU Yukun, YAN Yi, FU Meiwen

Materials Reports 2020,34(17 ):17072 -17076. DOI:10.11896/cldb.20050196

Abstract （648）

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Phase Stability of the Co_xMn_2-xCrFeNi High Entropy Alloys Article

TIAN Mengyun, WU Changjun, LIU Ya, PENG Haoping, WANG Jianhua, SU Xuping

Materials Reports 2020,34(17 ):17067 -17071. DOI:10.11896/cldb.19120159

Abstract （615）

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Preparation of FeCrNiCuAlSn_0.5 High-entropy Alloys Coating by Thermite Reaction Article

CHEN Gang, LUO Tao, SHEN Shucheng, TAO Tao, TANG Xiaotian, XUE Wei, XIA Yi

Materials Reports 2020,34(17 ):17047 -17051. DOI:10.11896/cldb.20060192

Abstract （599）

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