Article
Chemistry, Physical
Sang Hun Shim, Jongun Moon, Hesam Pouraliakbar, Byung Ju Lee, Sun Ig Hong, Hyoung Seop Kim
Summary: The addition of nitrogen significantly affects the microstructural evolution and mechanical properties of CoCrFeMnNi alloys, suppressing grain growth and enhancing alloy performance. It results in excellent tensile strength and elongation with substantial strain hardening, showing strong temperature dependence in yield strength likely due to friction stress induced by temperature-dependent obstacles.
JOURNAL OF ALLOYS AND COMPOUNDS
(2022)
Article
Nanoscience & Nanotechnology
Jin Meng, Yu Qiao, Yan Chen, Tian-Wei Liu, Tong Li, Hai-Ying Wang, Lan - Hong Dai
Summary: This study investigated the compression properties of CoCrFeMnNi high entropy alloy syntactic foam at liquid nitrogen temperature. The foam exhibited ultra-high strength and energy absorption capacity, especially at cryogenic conditions. The microstructural analysis revealed a high twinning activity and shear localization propensity in the foam matrix, which dispersed deformation and benefited energy absorption. Dynamic loading activated a phase transformation, further enhancing the strength and toughness of the foam. Deformation twinning and phase transformation acted as additional plastic deformation mechanisms, compensating for the limitations of low temperature and high strain rate loading.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2023)
Article
Nanoscience & Nanotechnology
E. Povolyaeva, S. Mironov, D. Shaysultanov, N. Stepanov, S. Zherebtsov
Summary: A new medium-entropy Fe-65(CoNi)(25)Cr9.5C0.5 alloy was investigated for its properties at room and liquid nitrogen temperatures. The alloy exhibited high strength, good ductility, and excellent fracture toughness at cryogenic temperatures. The microstructure analysis suggested a phase transition induced by deformation, and the cold-rolled alloy showed improved mechanical properties compared to the as-cast alloy. Substructure strengthening, interphase strengthening, and solid solution strengthening were identified as contributing factors to the alloy's enhanced performance.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2022)
Article
Materials Science, Multidisciplinary
Peng Gao, Zihao Ma, Ji Gu, Song Ni, Tao Suo, Yulong Li, Min Song, Yiu-Wing Mai, Xiaozhou Liao
Summary: In this study, a bulk CrCoNi medium-entropy alloy was found to exhibit exceptional combination of high strength and excellent ductility under high strain rates and low temperatures. This was mainly attributed to profuse deformation twinning and other factors contributing to grain refinement, work hardening, and excellent tensile strain.
SCIENCE CHINA-MATERIALS
(2022)
Article
Materials Science, Multidisciplinary
Junha Yang, Yong Hee Jo, Woojin An, Hyoung Seop Kim, Byeong-Joo Lee, Sunghak Lee, Hyokyung Sung, Seok Su Sohn
Summary: This study evaluated the fracture toughness of a metastable alloy at room and cryogenic temperatures and investigated the effects of deformation-induced martensitic transformation (DIMT) on fracture behavior. The results showed that high fracture toughness and ductile fracture mode were observed at room temperature, but the fracture toughness significantly decreased at cryogenic temperature. The morphology of the martensite had an impact on the fracture behavior, with the plate-type BCC martensite exhibiting lower toughness and brittle fracture mode compared to the lath-type BCC martensite.
Article
Chemistry, Physical
Bo Guan, Yitao Wang, Jianbo Li, Yu Zhang, Hao Wang, Yunchang Xin
Summary: The influence of strain rate on strain hardening behavior of CrCoNi medium-entropy alloy (MEA) was investigated, showing that flow stress and peak stress decrease with decreasing strain rate and increasing temperature. The strain rate sensitivity factor increases with deformation temperature, and a strong dependence of strain hardening behavior on strain rate was observed at high temperatures. The microstructural characterization revealed different effects of strain rate on samples deformed at different temperatures, with recrystallized grains decreasing with increasing strain rate at higher temperatures. It was also observed that recrystallized grains only formed at high strain rates for samples deformed at lower temperatures.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Chemistry, Physical
Li Chen, Zhanjiang Li, Pinqiang Dai, Peixin Fu, Qunhua Tang, Junfeng Chen
Summary: The feasibility of preparing Fe50Mn30Co10Cr10 high-entropy alloys via powder metallurgy was explored, and the effect of sintering temperature and deformation temperature on the microstructure and tensile properties of the alloy was investigated. The best combination of strength and ductility was obtained in the alloy sintered at 1000 degrees C, with a strongly temperature-dependent mechanical behavior.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Nanoscience & Nanotechnology
Qiuyu Gao, Ran Wei, Shilin Feng, Chen Chen, Zhenhua Han, Liangbin Chen, Tan Wang, Shaojie Wu, Fushan Li
Summary: This work presents a unique low-cost medium-entropy alloy (MEA) with ultra-high strength and ductility. The MEA exhibits a duplex partially recrystallized microstructure consisting of FCC and BCC phases, along with high density dislocations and nano-precipitates. It shows excellent yield strength and uniform elongation at both room temperature and cryogenic temperatures, as well as a high ultimate tensile strength at 77K. The excellent cryogenic mechanical properties can be attributed to various factors including high density dislocations, ultra-fine grains, nano-precipitates, Luders deformation, hetero-deformation-induced hardening, and deformation-induced martensitic transformation.
SCRIPTA MATERIALIA
(2023)
Article
Nanoscience & Nanotechnology
M. C. Zang, H. Z. Niu, H. R. Zhang, H. Tan, D. L. Zhang
Summary: The cryogenic tensile properties and deformation behavior of a metastable beta-Ti alloy Ti-15Mo-2Al were investigated, revealing superhigh ultimate tensile strength at 77 K and 20 K. The alloy shows high elongation-to-fracture at 77 K but drops sharply at 20 K, with enhanced work hardening rate and tensile strength at 77 K due to dynamic Hall-Patch effect. A serrated deformation occurs at 20 K, and cryogenic applications of the alloy are proposed to be feasible at temperatures not lower than 77 K.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2021)
Article
Materials Science, Multidisciplinary
Xianzhe Zhong, Qingming Zhang, Mingzhen Ma, Jing Xie, Mingze Wu, Siyuan Ren, Yongming Yan
Summary: The development of aerospace and military defense sectors has increased the demand for metals with enhanced mechanical properties under extreme conditions. Eutectic high entropy alloys (EHEAs) offer potential applications in these fields due to their excellent mechanical performance and good castability. In this study, the dynamic compressive properties and microstructural characteristics of Al1.19Co2CrFeNi1.81 EHEA were investigated at room temperature and liquid nitrogen temperature. The EHEA exhibited high strength and plasticity, particularly at liquid nitrogen temperature and high strain rate.
MATERIALS & DESIGN
(2022)
Article
Materials Science, Multidisciplinary
Yeonju Noh, Min-Su Lee, Umer Masood Chaudry, Tea-Sung Jun
Summary: This study investigates the mechanical properties and strain rate sensitivity of a commercial aluminum alloy at different temperatures. The results show that the alloy exhibits improved mechanical properties and a change in strain rate sensitivity at cryogenic temperatures. The study also analyzes the strengthening mechanisms and work-hardening behavior, and examines the dislocation structures using microscopy techniques.
MATERIALS CHARACTERIZATION
(2023)
Article
Chemistry, Physical
Jiale Yuan, Hanwen Zhang, Zhong Wang, Peide Han, Junwei Qiao
Summary: The L12-strengthened CoCrFeNiTi0.2 (at.%) high-entropy alloy exhibits excellent tensile mechanical properties at both room temperature and liquid nitrogen temperature. At 77 K, the alloy shows remarkable strength-plasticity synergy with a yield strength of about 900 MPa, ultimate tensile strength of 1500 MPa, and elongation of 50%. The strengthening strategy of coherent L12 precipitates provides guidance for the development of high-performance alloys.
Article
Materials Science, Multidisciplinary
Yongju Kim, Hyung Keun Park, Peyman Asghari-Rad, Jaimyun Jung, Jongun Moon, Hyoung Seop Kim
Summary: The constitutive modeling of CoCrFeMnNi high-entropy alloy at cryogenic and room temperatures has been investigated, showing enhanced ductility and strength at 77K due to the combination of sub-grain structure, twinning, and dislocations. A kinematic constitutive model with a critical twinning stress parameter was constructed to explain the twinning initiation criteria, showing good agreement with experimental data. Different modeling parameters were obtained for each temperature to account for the changing deformation behavior.
METALS AND MATERIALS INTERNATIONAL
(2021)
Article
Chemistry, Physical
D. Wang, J. Tan, C. J. Li, X. M. Qin, S. F. Guo
Summary: The novel Ti30Al25Zr25Nb20 high-entropy alloy exhibits good creep resistance at room temperature, showing high dislocation activation volume and low creep strain rate sensitive index value.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Chemistry, Physical
Wei Yue, Hongbo Fan, Weinan Ru, Zhaoxuan Wu, Zhixiong Zhang, Lunyong Zhang, Zhiliang Ning, Jianfei Sun, Shu Guo, Yongjiang Huang
Summary: Emerging high-entropy alloys (HEAs) exhibit superior mechanical properties due to a synergy of multiple deformation mechanisms and their interactions. In this study, in-situ tensile deformation of a CrMnFeCoNi HEA at room temperature was conducted, revealing the effects of dislocation activity, slip band activation, and interactions on strain hardening rate. The alloy demonstrated high fracture toughness, with cracks initiating at slip zones and grain boundaries and propagating gradually to final fracture.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Materials Science, Multidisciplinary
Wenke Wang, Jaimyun Jung, Chao Cui, Wenzhen Chen, Yang Yu, Peng Li, Wencong Zhang, Renlong Xiong, Hyoung Seop Kim
Summary: This work investigated the anisotropy variation of tensile flow stress for AZ31 magnesium alloys at different temperatures and tensile strains using the visco-plastic self-consistent model. The results showed that the anisotropy of flow stress weakened with increasing temperature and exhibited a slightly increasing stage followed by a continuously decreasing stage with increasing strain. Activation of basal slip and tension twinning contributed to the development of a (0002)//LD type texture during tension deformation, while activation of prismatic slip produced a < 10-10 >//LD type texture. The study found that the macroscopic average resolved shear stress decreased significantly with increasing temperature or strain, resulting in the decline of the tension deformation behavior anisotropy.
METALS AND MATERIALS INTERNATIONAL
(2023)
Article
Metallurgy & Metallurgical Engineering
Minseok Gwak, Jun Young Park, Sang Guk Jeong, Jae Bok Seol, Hyokyung Sung, Seokhwan Kim, Hyoung Seop Kim, Jung Gi Kim
Summary: In this study, the properties of Fe-Si alloy samples processed by additive manufacturing (AM) were estimated using the response surface methodology (RSM). Quadratic polynomial models based on RSM successfully predicted the density and hardness of AM-processed Fe-4.5Si alloy samples. The optimal conditions to manufacture Fe-4.5Si samples with the highest density and hardness combination were found based on the validated mathematical models.
STEEL RESEARCH INTERNATIONAL
(2023)
Article
Nanoscience & Nanotechnology
Jiajia Shen, Rita Goncalves, Yeon Taek Choi, J. G. Lopes, Jin Yang, N. Schell, Hyoung Seop Kim, J. P. Oliveira
Summary: This study establishes a correlation between welding process, microstructure, and mechanical properties, laying the foundations for the successful joining and application of welded joints based on high entropy alloys using low-cost arc-based welding technologies.
SCRIPTA MATERIALIA
(2023)
Article
Materials Science, Multidisciplinary
Farahnaz Haftlang, Jae Bok Seol, Alireza Zargaran, Jongun Moon, Hyoung Seop Kim
Summary: Maraging structural materials have been used for centuries, but their low ductility has limited their application. In this study, a dual-phase medium-entropy Fe68Ni10Mn10Co10Ti1.5Si0.5 maraging alloy with high strength (1.6 GPa) and enhanced ductility (-25%) is developed by injecting metastable austenite into the microstructure. The combination of metastability and heterogeneity achieved through heat treatment techniques can provide a breakthrough in developing maraging materials with large ductility.
Article
Chemistry, Physical
Soung Yeoul Ahn, Dong Geun Kim, Jeong Ah Lee, Eun Seong Kim, Sang Guk Jeong, Rae Eon Kim, Jungho Choe, Soon-Jik Hong, Pham Quang, Sunghak Lee, Hyoung Seop Kim
Summary: This study investigates the mechanical properties of CoCrFeMnNi high-entropy alloy (HEA) manufactured through direct energy deposition. The effect of strain rate on the mechanical properties was analyzed, and a Johnson-Cook constitutive model was employed for simulation. The results showed that the microstructural behavior of the HEA was influenced by strain localization and twin formation, which have significant implications for the design and development of HEAs under extreme environments.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Chemistry, Physical
Soung Yeoul Ahn, Farahnaz Haftlang, Eun Seong Kim, Sang Guk Jeong, Ji Sun Lee, Hyoung Seop Kim
Summary: Reinforcement by composite fabrication has been studied to improve the strength of high-entropy alloys (HEAs). In this study, CoCrFeMnNi+B4C high-entropy composite (HEC) parts were fabricated using the direct energy deposition process. The presence of B4C nano-particles hindered grain growth and caused elemental segregation, leading to the formation of carbide-rich regions. The B4C nano-particles also promoted the pinning effect of dislocations and provided dispersion hardening, resulting in high mechanical strength of the CoCrFeMnNi+B4C HEC.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Chemistry, Physical
Selim Kim, Dong Geun Kim, Minu Kim, Ki Jong Kim, Jae Min Lee, Joon Hyuk Lee, Hae-Won Cheong, Hyoung Seop Kim, Sunghak Lee
Summary: Various Al foams have been developed to meet the increasing demands for impact reduction in military, automotive, civil-engineering, and aerospace applications. Evaluating their energy-absorbing performance is challenging due to the rapid closure of interior pores. This study modified a split Hopkinson pressure bar (SHPB) to reliably evaluate the energy-absorbing performance of open- and closed-cell Al foams using the incident wave alone.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Nanoscience & Nanotechnology
Jungwan Lee, Sujung Son, Seok Su Sohn, Jae Wung Bae, Hyoung Seop Kim
Summary: Hot rolling induces dynamic recrystallization and dislocation-based microbands in metastable medium-entropy alloys, leading to deformation-induced martensitic transformation at ambient temperature. This phenomenon is not identifiable in the as-annealed counterparts. As a result, the as-hot-rolled states of these alloys exhibit approximately 43% total elongation and doubled yield strength.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2023)
Article
Nanoscience & Nanotechnology
Selim Kim, Hyungu Kang, Minu Kim, Ki Jong Kim, Jae Min Lee, Hae-Won Cheong, Hyoung Seop Kim, Sunghak Lee
Summary: This study suggests that stacks of thin aluminum sheets with fine rectangular or triangular grooves are effective materials for energy absorption. The energy-absorbing performance of these materials was evaluated using a modified split Hopkinson pressure bar (SHPB). The study found that the grooves shape, groove cavity fraction, and specimen thickness affect the energy-absorbing parameters, including impact momentum and maximum impact acceleration. Both impact momentum and maximum impact acceleration showed a continuous decrease as the specimen thickness increased or as the groove cavity fraction increased. The triangular grooved specimens exhibited greater reduction in impact momentum compared to the rectangular grooved specimens. The overall energy-absorbing performance of the triangular grooved specimens was better than that of the rectangular grooved specimens. Notably, in the triangular grooved specimens with a high cavity fraction, the triangular embossing intruded into the groove cavities, resembling a 'zipper' mechanism, further enhancing the effectiveness of energy absorption. This study presents a promising approach for developing grooved aluminum sheet stacks with reduced impact momentum and maximum impact acceleration by exploring suitable groove shapes, cavity fractions, and stack thicknesses, especially in dynamically compressed artillery environments.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2023)
Article
Nanoscience & Nanotechnology
Rae Eon Kim, Gang Hee Gu, Yeon Taek Choi, Jeong Ah Lee, Hyoung Seop Kim
Summary: Heterostructuring is a method for achieving a combination of strength and ductility, but its usage is limited due to poor formability. In this study, a new strategy for designing heterostructures optimized for non-uniform deformation is proposed. The fabricated inverse-gradient structure of cold-rolled CoCrFeMnNi high-entropy alloy sheets exhibited superior strength-ductility synergy and excellent bendability. This is attributed to the prevention of external cracks and reduced damage evolution caused by the inverse-gradient structure. Overall, the heterostructured high-entropy alloys demonstrated superior tensile properties and formability.
SCRIPTA MATERIALIA
(2023)
Article
Nanoscience & Nanotechnology
Shiyu Du, Tuanwei Zhang, Zhiming Jiao, Dan Zhao, Jianjun Wang, Renlong Xiong, Hyoung Seop Kim, Zhihua Wang
Summary: A novel strategy of designing analogous harmonic structures (AHS) is implemented to enhance the strength-ductility synergy in the Co-Cr-Ni-based medium-entropy alloy (MEA). The AHS-MEA achieves high yield strength of 1028 MPa, ultimate tensile strength of 1558 MPa, and considerable uniform elongation of 20%. The study provides new insights into the nanocrystalline formation mechanism and excellent strength-ductility synergy.
SCRIPTA MATERIALIA
(2023)
Article
Materials Science, Multidisciplinary
Sujung Son, Jungwan Lee, Peyman Asghari-Rad, Rae Eon Kim, Hyojin Park, Jae-il Jang, Wen Chen, Yoon-Uk Heo, Hyoung Seop Kim
Summary: This study successfully synthesized a hierarchically heterogeneous microstructure by combining eutectic high-entropy alloy and medium-entropy alloy powders through powder metallurgy-based severe plastic deformation method, achieving strong hetero-deformation-induced strengthening effect. This is of great significance for the development of HEAs.
MATERIALS RESEARCH LETTERS
(2023)
Article
Engineering, Manufacturing
Anatoliy Zavdoveev, Andrey Klapatyuk, Thierry Baudin, Eric MacDonald, Dhanesh Mohan, J. P. Oliveira, Alex Gajvoronskiy, Valeriy Poznyakov, Hyoung Seop Kim, Francois Brisset, Maksym Khokhlov, Mark Heaton, Massimo Rogante, Mykola Skoryk, Dmitry Vedel, Roman Kozin, Illya Klochkov, Sviatoslav Motrunich
Summary: This study proposes the wire arc additive manufacturing method for non-equimolar Co-Cr-Fe-Mn-Ni high-entropy alloy using gas metal arc welding (GMAW) with metal powder-cored wire (MPCW). The filler powder contains Co-Cr-Mn-Ni components in equal atomic amounts relative to each other with Fe metal stripe as a shield. This method allows for building high-entropy alloy samples with desired characteristics. It outperforms alternative methods such as vacuum melting, plasma arc melting, selective laser melting, or electron beam melting in multiple indicators.
ADDITIVE MANUFACTURING LETTERS
(2023)
Article
Materials Science, Multidisciplinary
Sang-Ho Oh, Yang-Jin Jeong, Sin-Hye Na, Jiman Kim, Byeong-Joo Lee
Summary: In this study, the fundamental reason for the formation of columnar Nb3Sn grains was investigated using a novel Monte Carlo Potts model. It was found that insufficient Sn at the interface leads to a decrease in thermodynamic driving force and the formation of columnar Nb3Sn grains. Possible ways to suppress columnar grain formation were suggested based on this understanding, and the difference in columnar grain fraction depending on the wire strand type was explored. A brief guideline for designing wire strand geometry to avoid columnar grain formation was proposed.
Article
Materials Science, Multidisciplinary
Jung Soo Lee, Guanglong Xu, Joung Sik Suh, Jun Ho Bae, Byeong-Chan Suh, Young Min Kim, Byeong-Joo Lee, Won-Seok Ko
Summary: Molecular dynamics simulations are used to study the deformation and twinning behavior of single-crystal Mg nanopillars under different loading orientations. The developed interatomic potential successfully reproduces the observed slip and twinning phenomena and provides insights into the nucleation and growth mechanisms of unconventional twins.
