High-entropy alloys (HEAs) are generally defined as solid solutions containing at least 5 constituent elements with concentrations between 5 and 35 atomic percent without the formation of intermetallic compounds. Currently, HEAs receive great attention as promising candidate materials for extreme environments due to their potentially desirable properties that result from their unique structural properties. In this review paper, we aim to introduce HEAs and explain their properties and related research by classifying them into three main categories, namely, mechanical properties, thermal properties, and electrochemical properties. Due to the high demand for structural materials in extreme environments, the mechanical properties of HEAs including strength, hardness, ductility, fatigue, and wear resistance are mainly described. Thermal and electrochemical properties, essential for the application of these alloys as structural materials, are also described.

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• Sintering Behavior and Mechanical Property of Transition Metal Carbide-Based Cermets by Spark Plasma Sintering
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Fe₃O₄/Fe/graphene nanocomposite powder is synthesized by electrical wire explosion of Fe wire and dispersed graphene in deionized water at room temperature. The structural and electrochemical characteristics of the powder are characterized by the field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, field-emission transmission electron microscopy, cyclic voltammetry, and galvanometric discharge-charge method. For comparison, Fe₃O₄/Fe nanocomposites are fabricated under the same conditions. The Fe₃O₄/Fe nanocomposite particles, around 15-30 nm in size, are highly encapsulated in a graphene matrix. The Fe₃O₄/Fe/graphene nanocomposite powder exhibits a high initial charge specific capacity of 878 mA/g and a high capacity retention of 91% (798 mA/g) after 50 cycles. The good electrochemical performance of the Fe₃O₄/Fe/graphene nanocomposite powder is clearly established by comparison of the results with those obtained for Fe₃O₄/Fe nanocomposite powder and is attributed to alleviation of volume change, good distribution of electrode active materials, and improved electrical conductivity upon the addition of graphene.

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• Preparation of magnetic metal and graphene hybrids with tunable morphological, structural and magnetic properties
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  Applied Surface Science.2019; 478: 733.     CrossRef

Tin is one of the most promising anode materials for next-generation lithium-ion batteries with a high energy density. However, the commercialization of tin-based anodes is still hindered due to the large volume change (over 260%) upon lithiation/delithiation cycling. To solve the problem, many efforts have been focused on enhancing structural stability of tin particles in electrodes. In this work, we synthesize tin nano-powders with an amorphous carbon layer on the surface and surroundings of the powder by electrical wire explosion in alcohol-based liquid media at room temperature. The morphology and microstructures of the powders are characterized by scanning electron microscopy, Xray diffraction, Raman spectroscopy, and transmission electron microscopy. The electrochemical properties of the powder for use as an anode material for lithium-ion battery are evaluated by cyclic voltammetry and a galvanometric dischargecharge method. It is shown that the carbon-coated tin nano-powders prepared in hexanol media exhibit a high initial charge specific capacity of 902 mAh/g and a high capacity retention of 89% after 50 cycles.

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• Optimization of carbon coating thickness to prevent crack generation in Sn nanoparticles during charge/discharge process and their electrochemical properties
  Ji-Seub Choi, Yeon-Ju Lee, Hoi-Jin Lee, Gyu-Bong Cho, Jai-Won Byeon, Hyo-Jun Ahn, Ki-Won Kim, Jou-Hyeon Ahn, Kwon-Koo Cho
  Journal of Alloys and Compounds.2020; 843: 155892.     CrossRef
• Fabrication of multilayer graphene-encapsulated Sn/SnO2 nanocomposite as an anode material for lithium-ion batteries and its electrochemical properties
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The electrochemical properties of cells assembled with the LiNiO₂ (LNO) recycled from cathode materials of waste lithium secondary batteries (Li[Ni,Co,Mn]O₂), were evaluated in this study. The leaching, neutralization and solvent extraction process were applied to produce high-purity NiSO₄ solution from waste lithium secondary batteries. High-purity NiO powder was then fabricated by the heat-treatment and mixing of the NiSO₄ solution and H₂C₂O₄. Finally, LiNiO₂ as a cathode material for lithium ion secondary batteries was synthesized by heat treatment and mixing of the NiO and Li₂CO₃ powders. We assembled the cells using the LiNiO₂ powders and evaluated the electrochemical properties. Subsequently, we evaluated the recycling possibility of the cathode materials for waste lithium secondary battery using the processes applied in this work.