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Functionally graded structure of a nitride-strengthened Mg_(2)Si-based hybrid composite

Journal of Magnesium and Alloys 2024年第3期12卷 1239-1256页

作者： Jeongho Yang Woongbeom Heogh Hogi Ju Sukhyun Kang Tae-Sik Jang Hyun-Do Jung Mohammad Jahazi Seung Chul Han Seong Je Park hyoung seop kim Susmita Bose Amit Bandyopadhyay Martin Byung-Guk Jun Young Won kim Dae-kyeom kim Rigoberto CAdvincula Clodualdo Aranas Jr Sang Hoon kim School of Mechanical Engineering Pusan National UniversityBusan 46241Republic of Korea Department of Mechanical Design Engineering Hanyang UniversitySeoul 04763Republic of Korea Process Research 3 Team LG Display Co.Ltd.PajuGyeonggi-do 10845Republic of Korea Department of Materials Science and Engineering Chosun UniversityGwangju 61452Republic of Korea Institute of Well-Aging Medicare&Chosun University LAMP Center Chosun UniversityGwangju 61452Republic of Korea Division of Materials Science and Engineering Hanyang UniversitySeoul 04763Republic of Korea Department of Mechanical Engineering École de Technologie SupérieureMontrealQuebec H3C 1K3Canada Material&Component Convergence R&D Center Korea Construction Equipment Technology InstituteGunsanJeollabuk-do 54002Republic of Korea School of Mechanical and Aerospace Engineering Nanyang Technological UniversitySingapore 639798Singapore Graduate Institute of Ferrous&Eco Materials Technology Pohang University of Science and TechnologyPohangGyeongsangbuk-do 37673Republic of Korea Advanced Institute for Materials Research Tohoku UniversitySendai 980-8577Japan Institute for Convergence Research and Education in Advanced Technology Yonsei UniversitySeoul 03722Republic of Korea School of Mechanical and Materials Engineering Washington State UniversityPullmanWashington 99164USA School of Mechanical Engineering Purdue UniversityWest LafayetteIndiana 47907USA Research Institute of Advanced Manufacturing Technology Korea Institute of Industrial TechnologyIncheon 21999Republic of Korea Department of Macromolecular Science and Engineering Case Western Reserve UniversityClevelandOhio 44106USA Department of Chemical and Biomolecular Engineering and Joint Institute for Advanced Materials University of TennesseeKnoxvilleTennessee 37996USA Center for Nanophase Materials and Sciences Oak Ridge National LaboratoryOak RidgeTennessee 37830USA Department of Mechanical Engineering University of New BrunswickFrederictonNew Brunswick E3B 5A3Cana

The ex-situ incorporation of the secondary SiC reinforcement,along with the in-situ incorporation of the tertiary and quaternary Mg_(3)N_(2) and Si_(3)N_(4) phases,in the primary matrix of Mg_(2)Si is employed in order to provide ultimate wear resistance based on the laser-irradiation-induced inclusion of N_(2) gas during laser powder bed *** is substantialized based on both the thermal diffusion-and chemical reactionbased metallurgy of the Mg_(2)Si–SiC/nitride hybrid *** study also proposes a functional platform for systematically modulating a functionally graded structure and modeling build-direction-dependent architectonics during additive *** strategy enables the development of a compositional gradient from the center to the edge of each melt pool of the Mg_(2)Si–SiC/nitride hybrid ***,the coefficient of friction of the hybrid composite exhibits a 309.3%decrease to–1.67 compared to–0.54 for the conventional nonreinforced Mg_(2)Si structure,while the tensile strength exhibits a 171.3%increase to 831.5 MPa compared to 485.3 MPa for the conventional *** outstanding mechanical behavior is due to the(1)the complementary and synergistic reinforcement effects of the SiC and nitride compounds,each of which possesses an intrinsically high hardness,and(2)the strong adhesion of these compounds to the Mg_(2)Si matrix despite their small sizes and low concentrations.

关键词： Laser powder bed fusion Mg_(2)Si-SiC/nitride hybrid composite Both the thermal diffusion-and chemical reaction-based metallurgy Functionally graded structure Compositional gradient Wear resistance.

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A neural network model for high entropy alloy design

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npj Computational Materials 2023年第1期9卷 1734-1746页

作者： Jaemin Wang Hyeonseok Kwon hyoung seop kim Byeong-Joo Lee Department of Materials Science and Engineering Pohang University of Science and Technology(POSTECH)Pohang 37673Republic of Korea Graduate Institute of Ferrous and Energy materials Technology(GIFT) Pohang University of Science and Technology(POSTECH)Pohang 37673Republic of Korea Center for Heterogenic Metal Additive Manufacturing Pohang University of Science and Technology(POSTECH)Pohang 37673Republic of Korea Institute for Convergence Research and Education in Advanced Technology Yonsei UniversitySeoul 03722Republic of Korea Advanced Institute for Materials Research(WPI-AIMR) Tohoku UniversitySendai 980-8577Japan

A neural network model is developed to search vast compositional space of high entropy alloys(HEAs).The model predicts the mechanical properties of HEAs better than several other ***’s because the special structure of the model helps the model understand the characteristics of constituent elements of *** addition,thermodynamics descriptors were utilized as input to the model so that the model predicts better by understanding the thermodynamic properties of HEAs.A conditional random search,which is good at finding local optimal values,was selected as the inverse predictor and designed two HEAs using the *** experimentally verified that the HEAs have the best combination of strength and ductility and this proves the validity of the model and alloy design *** strengthening mechanism of the designed HEAs is further discussed based on microstructure and lattice distortion *** present alloy design approach,specialized in finding multiple local optima,could help researchers design an infinite number of new alloys with interesting properties.

关键词： alloy alloys microstructure

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Origin of superior low-cycle fatigue resistance of an interstitial metastable high-entropy alloy

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Journal of Materials Science & Technology 2022年第20期115卷 115-128页

作者： Seyed Amir Arsalan Shams Jae Wung Bae Jae Nam kim hyoung seop kim Taekyung Lee Chong Soo Lee Graduate Institute of Ferrous Technology Pohang University of Science and TechnologyPohang 37673Republic of Korea Department of Materials Science and Engineering Pohang University of Science and TechnologyPohang 37673Republic of Korea School of Mechanical Engineering Pusan National UniversityBusan 46241Republic of Korea

In this study, the deformation behaviors and related microstructural evolutions were investigated in either monotonic or cyclic deformation modes in an interstitial metastable high-entropy alloy. These investigations aimed to reveal the mechanisms underlying the superior low-cycle fatigue(LCF) life of this alloy.A thermomechanical process was applied to induce fine-grained(FG) and coarse-grained(CG) microstructures in Fe–30Mn–10Co–10Cr–0.4C(atomic percentage) alloy. Their superior combination of strength and ductility was attributed to the appearance of deformation-induced ε-martensite and the presence of carbon. The CG alloy showed a greater volume fraction of ε-martensite than the FG alloy in the monotonic deformation mode, and vice versa in the cyclic mode. Such a disparity was interpreted in light of the back-stress effect of the relaxed γ-grain boundaries in the latter mode. Meanwhile, the γ-to-ε phase transformation under cyclic loading at low strain amplitudes(0.4%) barely led to an improved fatigue life as compared with that at higher strain amplitudes(≥ 0.55%). The high reversibility of partial dislocation motions under cyclic loading and delaying the formation of dislocation cells through the martensitic transformation could explain why the alloys investigated in this study exhibited a superior LCF life compared with high-entropy alloys reported in previous studies.

关键词： High-entropy alloy Transformation-induced plasticity Monotonic deformation Cyclic deformation Low-cycle fatigue Stacking faults

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Electroplasticity in the Al_(0.6) CoCrFeNiMn high entropy alloy subjected to electrically-assisted uniaxial tension

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Journal of Materials Science & Technology 2023年第17期148卷 209-221页

作者： Zhiqin Yang Jianxing Bao Chaogang Ding Sujung Son Zhiliang Ning Jie Xu Debin Shan Bin Guo hyoung seop kim State Key Laboratory of Precision Hot Processing Harbin Institute of TechnologyHarbin 150001China School of Materials Science and Engineering Harbin Institute of TechnologyHarbin 150001China Department of Materials Science and Engineering Pohang University of Science and TechnologyPohang 37673Republic of Korea Graduate Institute of Ferrous Technology Pohang University of Science and TechnologyPohang 37673Republic of Korea

Electrically assisted deformation(EAD)was adopted in this work to overcome the shortcomings such as poor formability and easy cracking in the processing of dual-phase the Al_(0.6) CoCrFeNiMn high entropy al-loy(HEA)at room *** of the Al_(0.6) CoCrFeNiMn HEA was studied systematically using electrically assisted uniaxial *** results showed that pulse current caused the temperature gradient along the tensile direction and the temperatures of the samples increased with the current *** flow stress decreased,and the elongation increased with increasing current density during the *** the current density was 30 A mm-2,the total elongation of the samples could be increased by 50%compared to that with no *** current can reduce local stress concentration and post-pone microcracks initiation in the body-centered cubic(BCC)phases,and hence can effectively inhibit cracks and *** dislocation tangles were opened by pulse current,and the dislocation recovery was enhanced at a high current *** with dilute solid solution alloys,the lattice distortion effect,the high fraction of the BCC phases,and the dislocations in HEAs can lead to the enhancement of the local Joule heating,which accelerated dislocation slip and dislocation *** study con-firms that EAD can effectively im prove the formability of HEAs and provides theoretical guidance and an experimental basis for forming HEAs components.

关键词： Electrically-assisted deformation Electroplasticity Microstructural evolution Tensile behavior High entropy alloys

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Fabrication of Fullerene-Reinforced Aluminum Matrix Nanocomposites

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Acta Metallurgica Sinica(English Letters) 2017年第10期30卷 973-982页

作者： Hamed Asgharzadeh Hamid Faraghi hyoung seop kim Department of Materials Engineering Faculty of Mechanical EngineeringUniversity of Tabriz Department of Materials Science and Engineering Pohang University of Science and Technology (POSTECH)

Fullerene-reinforced A1 matrix nanocomposites were fabricated by high-energy mechanical milling followed by consolidation through hot extrusion or high-pressure torsion（HPT）. The results indicate that a relatively homogeneous microstructure consisting of elongated, micrometer-sized A1 grains is formed in the hot-extruded specimens. However, the microstructure is not uniform along the radius of the HPT disks, which includes coarse grains near the center of the disk and ultrafine grains in the middle and along the edge of the specimen. Microstructural evaluations of the HPT disks indicate that A1 grain refinement occurs due to the addition of fullerene, as grain size is reduced to 60 nm from 118 nm. The formation of the harmful aluminum carbide phase is not detected during the fabrication of Al/C（60） nanocomposites. The hardness, yield stress, and ultimate tensile strength of the Al-2 vol.% C（60） nanocomposites are about 27-160% higher than those of the monolithic A1 samples, revealing the effective strengthening of fullerene particles in A1 matrix. Moreover,mechanical properties of the Al/fullerene nanocomposites are significantly enhanced（59-272%） by utilizing HPT in comparison to hot-extruded specimens due to their much finer A1 grain structure. The reduction in the number and the size of the dimples, as well as the formation of smooth regions on the tensile fracture surface of Al/C（60）, results in their overall lower ductility compared to monolithic Al.

关键词： Aluminum Fullerene High-pressure torsion Hot extrusion Microstructure Mechanical properties

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Brain metabolism in patients with vegetative state after post-resuscitated hypoxic-ischemic brain injury： statistical parametric mapping analysis of F-18 fluorodeoxyglucose positron emission tomography

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Chinese Medical Journal 2013年第5期126卷 888-894页

作者： Yong Wook kim hyoung seop kim Young-Sil An Department and Research Institute of Rehabilitation Medicine Yonsei University College of Medicine Seoul Republic of Korea Department of Physical Medicine and Rehabilitation NationalHealth Insurance Corporation Ilsan Hospital Gyonggi-doRepublic of Korea Department of Nuclear Medicine Ajou University School ofMedicine Suwon Republic of Korea

Background Hypoxic-ischemic brain injury （HIBI） after cardiopulmonary resuscitation is one of the most devastating neurological conditions that causing the impaired consciousness. However, there were few studies investigated the changes of brain metabolism in patients with vegetative state （VS） after post-resuscitated HIBI. This study aimed to analyze the change of overall brain metabolism and elucidated the brain area correlated with the level of consciousness （LOC） in patients with VS after post-resuscitated HIBI. Methods We consecutively enrolled 17 patients with VS after HIBI, who experienced cardiopulmonary resuscitation. Overall brain metabolism was measured by F-18 fluorodeoxyglucose positron emission tomography （F-18 FDG PET） and we compared regional brain metabolic patterns from 17 patients with those from 15 normal controls using voxel-by-voxel based statistical parametric mapping analysis. Additionally, we correlated the LOC measured by the JFK-coma recovery scale-revised of each patient with brain metabolism by covariance analysis. Results Compared with normal controls, the patients with VS after post-resuscitated HIBI revealed significantly decreased brain metabolism in bilateral precuneus, bilateral posterior cingulate gyrus, bilateral middle frontal gyri, bilateral superior parietal gyri, bilateral middle occipital gyri, bilateral precentral gyri （PFEw correctecd 〈0.0001 ）, and increased brain metabolism in bilateral insula, bilateral cerebella, and the brainstem （PFEWcorrectecd 〈0.0001 ）. In covariance analysis, the LOC was significantly correlated with brain metabolism in bilateral fusiform and superior temporal gyri （P uncorrected 〈0.005）. Conclusions Our study demonstrated that the precuneus, the posterior cingulate area and the frontoparietal cortex, which is a component of neural correlate for consciousness, may be relevant structure for impaired consciousness in patient with VS after post-resuscitated HIBI. In post-resuscitated HIBI, measuremen

关键词： hypoxic-ischemic brain injury vegetative state brain metabolism

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Voxel-based statistical analysis of cerebral glucose metabolism in patients with permanent vegetative state after acquired brain injury

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Chinese Medical Journal 2010年第20期123卷 2853-2857页

作者： Yong Wook kim hyoung seop kim Young-Sil An Sang Hee Im Department and Research Institute of Rehabilitation Medicine Yonsei University College of MedicineSeoulRepublic of Korea Department of Physical Medicine and Rehabilitation National Health Insurance Corporation Ilsan Hospital Gyonggi-doRepublic of Korea) Young-Sil An(Department of Nuclear MedicineAjou University School of MedicineSuwonRepublic of Korea Department of Nuclear Medicine Ajou University School of Medicine Suwon Republic of Korea Department of Rehabilitation Medicine Jeju National University School of MedicineJejuRepublic of Korea

Background Permanent vegetative state is defined as the impaired level of consciousness longer than 12 months after traumatic causes and 3 months after non-traumatic causes of brain injury. Although many studies assessed the cerebral metabolism in patients with acute and persistent vegetative state after brain injury, few studies investigated the cerebral metabolism in patients with permanent vegetative state. In this study, we performed the voxel-based analysis of cerebral glucose metabolism and investigated the relationship between regional cerebral glucose metabolism and the severity of impaired consciousness in patients with permanent vegetative state after acquired brain *** We compared the regional cerebral glucose metabolism as demonstrated by F-18 fluorodeoxyglucose positron emission tomography from 12 patients with permanent vegetative state after acquired brain injury with those from 12 control subjects. Additionally, covariance analysis was performed to identify regions where decreased changes in regional cerebral glucose metabolism significantly correlated with a decrease of level of consciousness measured by JFK-coma recovery scare. Statistical analysis was performed using statistical parametric *** Compared with controls, patients with permanent vegetative state demonstrated decreased cerebral glucose metabolism in the left precuneus, both posterior cingulate cortices, the left superior parietal lobule （Pcorrected 〈0.001）, and increased cerebral glucose metabolism in the both cerebellum and the right supramarginal cortices （Pcorrected 〈0.001）. In the covariance analysis, a decrease in the level of consciousness was significantly correlated with decreased cerebral glucose metabolism in the both posterior cingulate cortices （Puncorrected 〈0.005）.Conclusion Our findings suggest that the posteromedial parietal cortex, which are part of neural network for consciousness, may be relevant structure for pathophysiological mechanism in pat

关键词： cerebral glucose metabolism permanent vegetative state acquired brain injury

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Continuum understanding of twin formation near grain boundaries of FCC metals with low stacking fault energy

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npj Computational Materials 2017年第1期3卷 275-283页

作者： Jaimyun Jung Jae Ik Yoon Jung Gi kim Marat I.Latypov Jin You kim hyoung seop kim Department of Materials Science and Engineering Pohang University of Science and Technology(POSTECH)Pohang 37673Republic of Korea GT-CNRS UMI 2958 Georgia TechLorraine 57070 MetzFrance Pohang Research Laboratory Steel Products Research Group 1POSCOPohang 790-785Republic of Korea Center for High Entropy Alloys Pohang University of Science and Technology(POSTECH)Pohang 37673Republic of Korea

Deformation twinning from grain boundaries is often observed in face-centered cubic metals with low stacking fault *** of the possible factors that contribute to twinning origination from grain boundaries is the intergranular interactions during ***,the influence of mechanical interaction among grains on twin evolution has not been fully *** spite of extensive experimental and modeling efforts on correlating microstructural features with their twinning behavior,a clear relation among the large aggregate of grains is still *** this work,we characterize the micromechanics of grain-to-grain interactions that contribute to twin evolution by investigating the mechanical twins near grain boundaries using a full-field crystal plasticity simulation of a twinning-induced plasticity steel deformed in uniaxial tension at room *** are first observed through electron backscatter diffraction technique to obtain data to reconstruct a statistically equivalent microstructure through synthetic microstructure ***-to-grain micromechanical response is analyzed to assess the collective twinning behavior of the microstructural volume element under tensile *** of the simulated results reveal that grain interactions are capable of changing the local mechanical behavior near grain boundaries by transferring strain across grain boundary or localizing strain near grain boundary.

关键词： grain microstructure steel

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Super-resolving material microstructure image via deep learning for microstructure characterization and mechanical behavior analysis

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npj Computational Materials 2021年第1期7卷 867-877页

作者： Jaimyun Jung Juwon Na Hyung Keun Park Jeong Min Park Gyuwon kim Seungchul Lee hyoung seop kim Department of Materials AI&Big-Data Korea Institute of Materials Science(KIMS)Changwon-siRepublic of Korea Department of Mechanical Engineering Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea Department of Materials Science and Engineering Pohrepresent the average grainang University of Science and Technology(POSTECH)PohangRepublic of Korea Graduate School of Artificial Intelligence Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea Graduate Institute of Ferrous Technology Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea

The digitized format of microstructures,or digital microstructures,plays a crucial role in modern-day materials ***,the acquisition of digital microstructures through experimental means can be unsuccessful in delivering sufficient resolution that is necessary to capture all relevant geometric features of the *** resolution-sensitive microstructural features overlooked due to insufficient resolution may limit one’s ability to conduct a thorough microstructure characterization and material behavior analysis such as mechanical analysis based on numerical ***,a highly efficient super-resolution imaging based on deep learning is developed using a deep super-resolution residual network to super-resolved low-resolution(LR)microstructure data for microstructure characterization and finite element(FE)mechanical *** characterization and FE model based mechanical analysis using the super-resolved microstructure data not only proved to be as accurate as those based on high-resolution(HR)data but also provided insights on local microstructural features such as grain boundary normal and local stress distribution,which can be only partially considered or entirely disregarded in LR data-based analysis.

关键词： microstructure Microstructure analysis

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Body-centered-cubic martensite and the role on room-temperature tensile properties in Si-added SiVCrMnFeCo high-entropy alloys

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Journal of Materials Science & Technology 2021年第17期76卷 222-230页

作者： Yong Hee Jo Junha Yang Won-Mi Choi Kyung-Yeon Doh Donghwa Lee hyoung seop kim Byeong-Joo Lee Seok Su Sohn Sunghak Lee Center for High Entropy Alloys Pohang University of Science and TechnologyPohang 37673South Korea Department of Materials Science and Engineering Division of Advanced Materials SciencePohang University of Science and TechnologyPohang 37673South Korea Graduate Institute of Ferrous Technology Pohang University of Science and TechnologyPohang 37673South Korea Department of Materials Science and Engineering Korea UniversitySeoul 02841South Korea

We present a new class of metastable high-entropy alloys(HEAs),triggering deformation-induced martensitic transformation(DIMT)from face-centered-cubic(FCC)to body-centered-cubic(BCC),i.e.,*** the ab-initio calculation based on 1 st order axial interaction model and combined with the Gibbs free energy calculation,the addition of Si is considered as a critical element which enables to reduce the intrinsic stacking fault energy(ISFE)in Si_xV_((9-x))Cr_(10)Mn_5 Fe_(46)Co_(30)(x=2,4,and 7 at.%)alloy *** ISFE decreases from-30.4 to-35.5 mJ/m^(2)as the Si content increases from 2 to 7 at.%,which well corresponds to the reduced phase stability of FCC against *** BCC-DIMT occurs in all the alloys via intermediate HCP martensite,and the HCP martensite provides nucleation sites of BCC ***,the transformation rate enhances as the Si content increases in an earlier deformation ra ***,the BCC-DIMT is also affected by the phase stability of FCC against BCC,and the stability is the highest at the Si content of 7 at.%.Thus,the 7Si alloy presents the moderate transformation rate in the later deformation *** to the well-controlled transformation rate and consequent strain-ha rdening rate,the 7Si alloy possesses the superior combination of strength and ductility beyond 1 GPa of tensile strength at room *** results suggest that the Si addition can be a favorable candidate in various metastable HEAs for the further property improvement.

关键词： High-entropy alloy(HEA) Deformation-induced martensitic transformation(DIMT) Phase stability Stacking fault energy(SFE)

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