• 한국분말재료학회지
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• 제30권6호
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• pp.478-483
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• 2023

High-entropy alloys (HEAs) are characterized by having five or more main elements and forming simple solids without forming intermetallic compounds, owing to the high entropy effect. HEAs with these characteristics are being researched as structural materials for extreme environments. Conventional refractory alloys have excellent high-temperature strength and stability; however, problems occur when they are used extensively in a high-temperature environment, leading to reduced fatigue properties due to oxidation or a limited service life. In contrast, refractory entropy alloys, which provide refractory properties to entropy alloys, can address these issues and improve the high-temperature stability of the alloy through phase control when designed based on existing refractory alloy elements. Refractory high-entropy alloys require sufficient milling time while in the process of mechanical alloying because of the brittleness of the added elements. Consequently, the high-energy milling process must be optimized because of the possibility of contamination of the alloyed powder during prolonged milling. In this study, we investigated the high-temperature oxidation behavior of refractory high-entropy alloys while optimizing the milling time.

• 한국분말재료학회지
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• 제25권3호
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• pp.208-212
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• 2018

In this paper, a new $Co_{10}Fe_{10}Mn_{35}Ni_{35}Zn_{10}$ high entropy alloy (HEA) is identified as a strong candidate for the single face-centered cubic (FCC) structure screened using the upgraded TCFE2000 thermodynamic CALPHAD database. The $Co_{10}Fe_{10}Mn_{35}Ni_{35}Zn_{10}$ HEA is fabricated using the mechanical (MA) procedure and pressure-less sintering method. The $Co_{10}Fe_{10}Mn_{35}Ni_{35}Zn_{10}$ HEA, which consists of elements with a large difference in melting point and atomic size, is successfully fabricated using powder metallurgy techniques. The MA behavior, microstructure, and mechanical properties of the $Co_{10}Fe_{10}Mn_{35}Ni_{35}Zn_{10}$ HEA are systematically studied to understand the MA behavior and develop advanced techniques for fabricating HEA products. After MA, a single FCC phase is found. After sintering at $900^{\circ}C$, the microstructure has an FCC single phase with an average grain size of $18{\mu}m$. Finally, the $Co_{10}Fe_{10}Mn_{35}Ni_{35}Zn_{10}$ HEA has a compressive yield strength of 302 MPa.

• 한국재료학회지
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• 제33권3호
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• pp.95-100
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• 2023

This research examines the effect of adding aluminum on the structural, phasic, and magnetic properties of CoCrFe NiMnAl_x high-entropy alloys. To this aim, the arc-melt process was used under an argon atmosphere for preparing cast samples. The phasic, structural, and magnetic properties of the samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrational magnetometry (VSM) analyses. Based on the results, the addition of aluminum to the compound caused changes in the crystalline structure, from FCC solid solution in the CoCrFeNiMn sample to CoCrFeNiMnAl BBC solid solution. It was associated with changes in the magnetic property of CoCrFeNiMnAl_x high-entropy alloys, from paramagnetic to ferromagnetic. The maximum saturation magnetization for the CoCrFeNiMnAl casting sample was estimated to be around 79 emu/g. Despite the phase stability of the FCC solid solution with temperature, the solid solution phase formed in the CrCrFeNiMnAl high-entropy compound was not stable, and changed into FCC solid solution with temperature elevation, causing a reduction in saturation magnetization to about 7 emu/g.

• 소성∙가공
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• 제31권5호
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• pp.273-280
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• 2022

Although the mechanical properties of high-entropy alloys depend on the annealing conditions, limited works were established to investigate the annealing effect on the mechanical properties of Mo-added high-entropy alloys. Therefore, in the present work, the annealing effects on the microstructural evolution and mechanical properties of Mo-added high-entropy alloy were investigated. As a result, incomplete recrystallization from the limited annealing time not only suppresses deformation-induced phase transformation during cryogenic tensile test but also induces a deformation instability that results into the ductility reduction compare with the fully recrystallized sample. This result represents adjustment of annealing time is useful to control both transformation-induce plasticity and deformation instability of high-entropy alloys, and this can be applied to control the mechanical properties of metallic alloys by combining pre-straining and subsequent annealing.

• Archives of Metallurgy and Materials
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• 제65권3호
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• pp.1005-1009
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• 2020

In this study, a non-equiatomic high entropy alloy was fabricated using the spark plasma sintering method, and its microstructural features and mechanical properties were investigated. The chemical composition of FeMnCoCr was determined by using the entropy calculation related to the design of high entropy alloys. A bulk sample with the same composition was also prepared using the conventional metallurgical processes of casting and hot rolling. The microstructures of the samples fabricated by these different processes were compared by microscope observation, and a quantitative phase analysis was carried out using FE-SEM. Hardness measurement was used to evaluate mechanical properties. Particular attention was paid to microstructural changes due to heat treatment, which was analyzed by considering how austenite stability is affected by grain refinement.

• Archives of Metallurgy and Materials
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• 제66권3호
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• pp.703-707
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• 2021

In this work, we have designed a new high entropy alloy containing lightweight elements, e.g., Al, Fe, Mn, Ti, Cu, Si by high energy ball milling and spark plasma sintering. The composition of Si was kept at 0.75 at% in this study. The results showed that the produced AlCuFeMnTiSi_0.75 high entropy alloy was BCC structured. The evolution of BCC1 and BCC2 phases was observed with increasing the milling time up to 60 h. The spark plasma sintering treatment of milled compacts from 650-950℃ showed the phase separation of BCC into BCC1 and BCC2. The density and strength of these developed high entropy alloys (95-98%, and 1000 HV) improved with milling time and were maximum at 850℃ sintering temperature. The current work demonstrated desirable possibilities of Al-Si based high entropy alloys for substitution of traditional cast components at intermediate temperature applications.

• 한국분말재료학회지
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• 제28권2호
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• pp.103-109
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• 2021

High-entropy alloys have excellent mechanical properties under extreme environments, rendering them promising candidates for next-generation structural materials. It is desirable to develop non-equiatomic high-entropy alloys that do not require many expensive or heavy elements, contrary to the requirements of typical high-entropy alloys. In this study, a non-equiatomic high-entropy alloy powder Fe_49.5Mn₃₀Co₁₀Cr₁₀C_0.5 (at.%) is prepared by high energy ball milling and fabricated by spark plasma sintering. By combining different ball milling times and ball-to-powder ratios, we attempt to find a proper mechanical alloying condition to achieve improved mechanical properties. The milled powder and sintered specimens are examined using X-ray diffraction to investigate the progress of mechanical alloying and microstructural changes. A miniature tensile specimen after sintering is used to investigate the mechanical properties. Furthermore, quantitative analysis of the microstructure is performed using electron backscatter diffraction.

• Archives of Metallurgy and Materials
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• 제65권4호
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• pp.1269-1272
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• 2020

In this study, a molybdenum alloy with dispersed high-entropy particles was fabricated using the powder metallurgy method. The high-entropy powder, composed of Nb, Ta, V, W, and Zr elements with a same atomic fraction, was prepared via high-energy ball milling. Using this powder, an ideal core-shell powder, composed of high-entropy powder as core and Mo powder as shell, was synthesized via the milling and reduction processes. These processes enabled the realization of an ideal microstructure with the high-entropy phase uniformly dispersed in the Mo matrix. The sintered body was successfully fabricated via uniaxial compaction followed by pressureless sintering. The sintered body was analyzed by X-ray diffraction and scanning electron microscope, and the high-entropy phase is uniformly dispersed in the Mo matrix.

• 한국분말재료학회지
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• 제26권6호
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• pp.515-527
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• 2019

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.

• Archives of Metallurgy and Materials
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• 제67권4호
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• pp.1543-1546
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• 2022

The aluminum composite with dispersed high entropy alloy were developed by stir casting involving the powder-in-tube method. First, Al_0.5CoCrCuFeNi high entropy alloy (HEA) powder was made by mechanical alloying, and the powder was extruded in a tube-type aluminum container to form HEA precursor. The extruded HEA precursor was then dispersed in the aluminum matrix via stir casting. As a result, Fe-Cr-Ni based high-entropy phases was uniformly formed in the aluminum matrix, revealing ~158, 166, 235% enhancement of tensile strength by incorporating 1, 3, and 5 wt% HEA particles, respectively.