• Title/Summary/Keyword: high entropy alloy

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FABRICATION OF MOLYBDENUM ALLOY WITH DISTRIBUTED HIGH-ENTROPY ALLOY VIA PRESSURELESS SINTERING

  • WON JUNE CHOI;CHEONWOONG PARK;JONGMIN BYUN;YOUNG DO KIM
    • Archives of Metallurgy and Materials
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    • v.65 no.4
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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.

Thermal Stability and Weight Reduction of Al0.75V2.82CrZr Refractory High Entropy Alloy Prepared Via Mechanical Alloying (기계적 합금화를 이용한 Al0.75V2.82CrZr 내화 고엔트로피 합금의 경량화 및 고온 열안정성 연구)

  • Minsu Kim;Hansung Lee;Byungmin Ahn
    • Journal of Powder Materials
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    • v.30 no.6
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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.

Microstructural Evolution of AlCuFeMnTi-0.75Si High Entropy Alloy Processed by Mechanical Alloying and Spark Plasma Sintering

  • Minsu Kim;Ashutosh Sharma;Myoung Jin Chae;Hansung Lee;Byungmin Ahn
    • Archives of Metallurgy and Materials
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    • v.66 no.3
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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 AlCuFeMnTiSi0.75 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.

MICROSTRUCTURAL AND MECHANICAL CHARACTERISTICS OF NON-EQUIATOMIC HIGH ENTROPY ALLOY FeMnCoCr PREPARED BY SPARK PLASMA SINTERING

  • NAMHYUK SEO;JUNHYUB JEON;SEUNGGYU CHOI;YOUNG HOON MOON;IN-JIN SHON;SEOK-JAE LEE
    • Archives of Metallurgy and Materials
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    • v.65 no.3
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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.

Influence of Milling Conditions on the Microstructural Characteristics and Mechanical Properties of Non-equiatomic High Entropy Alloy (밀링 조건이 고엔트로피 합금의 미세조직 및 기계적 특성에 미치는 영향)

  • Seo, Namhyuk;Jeon, Junhyub;Kim, Gwanghoon;Park, Jungbin;Son, Seung Bae;Lee, Seok-Jae
    • Journal of Powder Materials
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    • v.28 no.2
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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 Fe49.5Mn30Co10Cr10C0.5 (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.

Effect of Milling Time on the Microstructure and Mechanical Properties of Ta20Nb20V20W20Ti20 High Entropy Alloy (Ta20Nb20V20W20Ti20 하이엔트로피 합금의 미세조직 및 기계적 특성에 미치는 밀링 시간의 영향)

  • Song, Da Hye;Kim, Yeong Gyeom;Lee, Jin Kyu
    • Journal of Powder Materials
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    • v.27 no.1
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    • pp.52-57
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    • 2020
  • In this study, we report the microstructure and characterization of Ta20Nb20V20W20Ti20 high-entropy alloy powders and sintered samples. The effects of milling time on the microstructure and mechanical properties were investigated in detail. Microstructure and structural characterization were performed by scanning electron microscopy and X-ray diffraction. The mechanical properties of the sintered samples were analyzed through a compressive test at room temperature with a strain rate of 1 × 10-4 s-1. The microstructure of sintered Ta20Nb20V20W20Ti20 high-entropy alloy is composed of a BCC phase and a TiO phase. A better combination of compressive strength and strain was achieved by using prealloyed Ta20Nb20V20W20Ti20 powder with low oxygen content. The results suggest that the oxide formed during the sintering process affects the mechanical properties of Ta20Nb20V20W20Ti20 high-entropy alloys, which are related to the interfacial stability between the BCC matrix and TiO phase.

Annealing Effect on the Mechanical Properties of Hot-Rolled Fe55Co17.5Ni10Cr12.5Mo5 High-Entropy Alloy (열간압연 된 Fe55Co17.5Ni10Cr12.5Mo5 고엔트로피합금의 소둔 조건에 따른 기계적 특성 변화)

  • Park, H.D.;Bae, D.H.;Won, J.W.;Moon, J.;Kim, H.S.;Seol, J.B.;Sung, H.;Bae, J.W.;Kim, J.G.
    • Transactions of Materials Processing
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    • v.31 no.5
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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.

Effects of Heat Treatment on Secondary Phase Formation and Nanoindentation Creep Behavior of Nanocrystalline CoCrFeMnNi High-entropy alloy (나노결정립 CoCrFeMnNi 고엔트로피합금의 열처리에 따른 이차상 형성 및 나노압입 크리프 거동 변화 연구)

  • Dong-Hyun Lee;Jae-il Jang
    • Journal of the Korean Society for Heat Treatment
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    • v.36 no.3
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    • pp.128-136
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    • 2023
  • In this study, the effects of heat treatment on the nano-scale creep behavior of CoCrFeMnNi high-entropy alloy (HEA) processed by high-pressure torsion (HPT) was investigated through nanoindentation technique. Nanoindentation experiments with a Berkovich indenter were performed on HPT-processed alloy subjected to heat treatment at 450℃, revealing that the hardness of the HPT-processed alloy (HPT sample) significantly increased with the heat treatment time. The heat treatment-induced microstructural change in HPT-processed alloy was analyzed using transmission electron microscopy, which showed the nano-sized Cr-, NiMn-, and FeCo-rich phases were formed in the HPT-processed alloy subjected to 10 hours of heat treatment (HPT+10A sample). To compare the creep behavior of HPT and HPT+10A samples, constant load nanoindentation creep experiments were performed using spherical indentation indenters with two different radii. It was revealed that the predominant mechanism for creep highly depended on the applied stress level. At low stress level, both HPT and HPT+10A samples were dominated by Coble creep. At high stress level, however, the mechanism transformed to dislocation creep for HPT sample, but continued to be Coble creep for HPT+10A sample, leading to higher creep resistance in the HPT+10A sample.

New Co10Fe10Mn35Ni35Zn10 high-entropy alloy Fabricated by Powder Metallurgy (분말야금법으로 제조한 새로운 Co10Fe10Mn35Ni35Zn10 고엔트로피 합금)

  • Yim, Dami;Park, Hyung Keun;Tapia, Antonio Joao Seco Ferreira;Lee, Byeong-Joo;Kim, Hyoung Seop
    • Journal of Powder Materials
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    • v.25 no.3
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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.

Structural Characterization of CoCrFeMnNi High Entropy Alloy Oxynitride Thin Film Grown by Sputtering (스퍼터링 방법으로 성장한 코발트크롬철망간니켈 고엔트로피 질산화물 박막의 구조특성)

  • Lee, Jeongkuk;Hong, Soon-Ku
    • Korean Journal of Materials Research
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    • v.28 no.10
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    • pp.595-600
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    • 2018
  • This study investigates the microstructural properties of CoCrFeMnNi high entropy alloy (HEA) oxynitride thin film. The HEA oxynitride thin film is grown by the magnetron sputtering method using nitrogen and oxygen gases. The grown CoCrFeMnNi HEA film shows a microstructure with nanocrystalline regions of 5~20 nm in the amorphous region, which is confirmed by high-resolution transmission electron microscopy (HR-TEM). From the TEM electron diffraction pattern analysis crystal structure is determined to be a face centered cubic (FCC) structure with a lattice constant of 0.491 nm, which is larger than that of CoCrFeMnNi HEA. The HEA oxynitride film shows a single phase in which constituting elements are distributed homogeneously as confirmed by element mapping using a Cs-corrected scanning TEM (STEM). Mechanical properties of the CoCrFeMnNi HEA oxynitride thin film are addressed by a nano indentation method, and a hardness of 8.13 GPa and a Young's modulus of 157.3 GPa are obtained. The observed high hardness value is thought to be the result of hardening due to the nanocrystalline microstructure.