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Grain size and temperature effect on the tensile behavior and deformation mechanisms of non-equiatomic Fe(41)Mn(25)Ni(24)Co8Cr2high entropy alloy

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journal of Materials Science & Technology 2020年第7期42卷 190-202页

作者： H.T.jeong W.j.kim Department of Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul121-791Republic of Korea

The effect of the grain size on the tensile properties and deformation mechanisms of a nonequiatomic Fe(41)Mn(25)Ni(24)Co8 Cr2 high-entropy alloy was studied in the temperature range between 298 and 1173 k by preparing the samples with three different grain sizes through severe plastic deformation and subsequent annealing:ultrafine(sub)grain size(≤0.5μm),8.1μm and 590.2μ*** the temperature between 298 and773 k,the material with the large grain size of 590.2μm exhibited the largest tensile ductility(57%-82%)due to its high strain hardening associated with mechanical twinning,but it exhibited the lowest strength due to its large grain *** material with the ultrafine(sub)grain size exhibited the lowest tensile ductility(3%-7%)due to a greatly reduced strain hardening ability after severe plastic deformation,but it exhibited the highest strength due to the dislocation strengthening and grain refinement *** tensile testing at temperatures above 973 k,recrystallization occurred in the material with the ultrafine(sub)grains during the sample heating and holding stage,leading to the formation of fine and equiaxed grains with the sizes of 6.8-13.5μ*** deformation behavior of the Fe(41)Mn(25)Ni(24)Co8 Cr2 with different grain sizes in the high temperature range between 973 and 1173 k,where pseudosteady-state flow was attained in the stress-strain curves,could be explained by considering the simultaneous contribution of grain boundary sliding and dislocation-climb creep to total plastic *** activation energies for plastic flow for the materials with different grain sizes were similar as^199 kj/*** predicting the deformation mechanism,it was important to consider the change in grain size by rapid grain growth or recrystallization during the sample heating and holding stage because grain boundary sliding is a grain-size-dependent deformation *** sample with the ultrafine(sub)grains exhibited the large tensile elongations of 30%-85%due to it

关键词： High entropy alloys Grain size High temperature deformation mechanism Tensile behavior Grain boundary sliding

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Microstructure tailoring of Al_(0.5)CoCrFeMnNi to achieve high strength and high uniform strain using severe plastic deformation and an annealing treatment

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journal of Materials Science & Technology 2021年第12期71卷 228-240页

作者： H.T.jeong W.j.kim Department of Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul 121-791Republic of Korea

Ultrafine-grained alloys fabricated by severe plastic deformation(SPD)have high strength but often poor uniform *** via high-ratio differential speed rolling(HRDSR)followed by an annealing treatment was applied to Al_(0.5)CoCrFeMnNi to design the microstructure from which both high strength and high uniform strain can be *** optimized microstructure was composed of an ultrafine-grained FCC matrix(1.7-2μm)with a high fraction of high-angle grain boundaries(61%-66%)and ultrafine BCC particles(with a size of 0.6-1μm and a volume fraction of8%-9.3%)distributed uniformly at the grain boundaries of the FCC *** the severely plastically deformed microstructure,the nucleation kinetics of the BCC phase was *** static recrystallization(CSRX)took place during the annealing process at 1273 *** of the BCC phase particles occurring concurrently with CSRX effectively retarded the grain growth of the FCC *** precipitation of the hard and brittleσphase was,however,*** annealed sample processed by HRDSR with the optimized microstructure exhibited a high tensile strength of over 1 GPa with a good uniform elongation of 14%-20%.These tensile properties are comparable to those of transformation-induced plasticity *** mechanisms of the severely plastically deformed alloy before and after annealing were identified,and each strengthening mechanism contribution was *** calculated results matched well with the experimental results.

关键词： High entropy alloys Severe plastic deformation Uniform ductility High strength Dual phase Annealing

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Effects of grain size and Al addition on the activation volume and strain-rate sensitivity of CoCrFeMnNi high-entropy alloy

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journal of Materials Science & Technology 2023年第12期143卷 242-252页

作者： H.T.jeong W.j.kim Department of Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul121-791Republic of Korea

The activation volume(V∗)and strain-rate sensitivity exponent(m)of CoCrFeMnNi and Al_(0.5)CoCrFeMnNi high entropy alloys(HEAs)with various grain sizes(ranging between 2.4 and 356μm)were measured at different strain rates and strain levels at room *** the strain rate decreased,the plastic strain decreased,and the grain size increased,V∗*** enhanced solid-solution strengthening by addition of aluminum decreased V∗.The Hassen plot was modified to capture the grain-size depen-dence of V∗by considering the grain-size dependence of the dislocation *** the plastic strain increased,the strain rate decreased,and the grain size decreased,m *** behavior of m could be quantitatively predicted by using equations derived for the grain-size-dependent V∗and flow *** difference in the grain-size dependence of m between conventional face centered cubic(FCC)metals and FCC HEAs over the nanograin size range could not be explained in terms of a relatively large Hall-Petch slope of the FCC HEAs compared with that of the FCC conventional metals,but was explainable in terms of a substantially higher probability of activation of grain-boundary diffusion-controlled grain-boundary-sliding mechanism at nanograin sizes in the FCC conventional metals than in the FCC HEAs.

关键词： Grain size High entropy alloys Activation volume Strain-rate sensitivity Solid solution

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Nrf2 is required for normal postnatal bone acquisition in mice

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Bone Research 2014年第4期2卷 231-240页

作者： jung-Hyun kim Vandana Singhal Shyam Biswal Rajesh k Thimmulappa Douglas j Di Girolamo Department of Environmental Health Sciences Johns Hopkins Bloomberg School of Public HealthBaltimoreMDUSA Department of Orthopaedic Surgery Johns Hopkins University School of MedicineBaltimoreMDUSA

A large body of literature suggests that bone metabolism is susceptible to the ill effects of reactive species that accumulate in the body and cause cellular dysfunction. One of the body＇s front lines in defense against such damage is the transcription factor, Nrf2. This transcription factor regulates a plethora of antioxidant and cellular defense pathways to protect cells from such damage. Despite the breadth of knowledge of both the function of Nrf2 and the effects of reactive species in bone metabolism, the direct role of Nrf2 in skeletal biology has yet to be thoroughly examined. Thus, in the current study, we have examined the role of Nrf2 in postnatal bone metabolism in mice. Mice lacking Nrf2 （Nrf2-/-） exhibited a marked deficit in postnatal bone acquisition, which was most severe at 3 weeks of age when osteoblast numbers were 12-fold less than observed in control animals. While primary osteoblasts from Nrf2-/- mice functioned normally in vitro, the colony forming capacity of bone marrow stromal cells （BMSCs） from these mice was significantly reduced compared to controls. This defect could be rescued through treatment with the radical scavenger N-acetyl cysteine （NAC）, suggesting that increased reactive species stress might impair early osteoblastogenesis in BMSCs and lead to the failure of bone acquisition observed in Nrf2-/- animals. Taken together, these studies suggest Nrf2 represents a key pathway in regulating bone metabolism, which may provide future therapeutic targets to treat osteoporosis.

关键词： bone Nrf2 is required for normal postnatal bone acquisition in mice

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Effect of Ca addition on the microstructure and mechanical properties of heat-treated Mg-6.0Zn-1.2Y-0.7Zr alloy

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journal of Magnesium and Alloys 2021年第5期9卷 1636-1648页

作者： Young Gil jung Wonseok Yang Yong joo kim Shae.k.kim Young Ok Yoon Hyunkyu Lim Do Hyang kim Advanced Materials and Process R&D Department Korea Institute of Industrial Technology156Gaetbeol-roIncheon 21999Republic of Korea Department of Metallurgical Engineering Yonsei University50Yonsei-roSeoulSeodaemun-gu 03722Republic of Korea

In this study,the effects of Ca addition on the microstructure,thermal properties,and mechanical properties of a Mg-6.0Zn-1.2Y-0.7Zr(ZWk611)alloy at room temperature and 150℃ were *** an increase in the Ca content,the ignition resistance of the ZWk611 alloy improved and the grains became *** as-cast ZWk611 alloy consisted mainly of the dendriticα-Mg matrix and I-phase(Mg_(3)Zn_(6)Y)at the grain *** the other hand,theτ-(Ca_(2)Mg_(6)Zn_(3))and I-phases were formed in the Ca-added ZWk611 *** fraction of theτ-phase increased with an increase in the Ca *** the solid-solution treatment,these phases remained partially at the grain boundaries of the Ca-added ZWk611 alloys and an additional W-phase(Mg_(3)Zn_(3)Y)was *** phases remaining at the grain boundaries restricted the grain growth through the grain boundary pinning *** aging treatment resulted in the formation of MgZn'precipitates in theα-Mg matrix of the *** precipitates were more uniformly distributed in the Ca-added alloys than in the alloys without ***,the heat treatment-induced precipitation improved the tensile and creep properties of the T6-treated *** T6-treated ZWk611+0.7Ca alloy exhibited the best mechanical properties at room temperature and 150℃ among all the tested alloys.

关键词： Mg-Zn-Y alloys Heat-treatment Precipitate Mechanical properties Thermal analysis

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Effect of Alloying Elements on Microstructure,Martensitic Transformation and Mechanical Properties of Ni-Mn Based Alloys

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journal of Materials Science & Technology 2009年第5期25卷 649-654页

作者： k.Alvarez H.Y.kim S.Miyazaki Graduate School University of TsukubaIbaraki 305-8573Japan Institute of Materials Science University of TsukubaTsukubaIbaraki 305-8573Japan

The microstructural features, shape memory behavior and mechanical properties of Ni-Mn based alloys were investigated by differential scanning calorimetry （DSC）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and thermal cycling test under various stresses. The transformation temperatures shifted toward lower temperatures when adding a third element into the Ni-Mn system. The addition of 10 at. pct Fe increased considerably the mechanical properties exhibiting still high transformation temperatures. However, it was found that in NiMn40Fe10 alloy the martensitic transformation is not thermoelastic in nature. The mechanism of this transformation and the crystallography of Ni-Mn（50-x）-Fex （x=5, 7, 10, 20 at. pct） alloys are presented.

关键词： Ni-Mn based alloys Martensitic transformation temperature L10 phase

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The Stanley Neuropathology Consortium Integrative Database (SNCID) for Psychiatric Disorders

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Neuroscience Bulletin 2019年第2期35卷 277-282页

作者： Sanghyeon kim Maree j.Webster Stanley Brain Research Laboratory Stanley Medical Research Institute

The Stanley Medical Research Institute(SMRI)is a nonprofit organization with a primary mission to fund research on the cause and treatment of severe mental *** SMRI also supports a brain bank as part of the mission to facilitate research into mental *** SMRI brain bank distributes postmortem samples from individuals with serious mental illness,free of charge,to scientists around the *** SMRI brain bank is recognized for the unique way it is set up,organized,and *** of demographically-matched groups of patients with schizophrenia,bipolar disorder(BP),or major depression(DEP)and unaffected controls are organized such that all researchers applying for tissue received samples from the same cohort.

关键词： SNCID for Psychiatric Disorders DRD RNA

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Aqueous-processable,naphthalene diimide-based polymers for eco-friendly fabrication of high-performance,n-type organic electrolyte-gated transistors

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Science China Chemistry 2022年第5期65卷 973-978页

作者： Dahyun jeong Min je kim Seungjin Lee jin-Woo Lee Youngwoong kim Hyeong jun kim jeong Ho Cho Bumjoon j.kim Department of Chemical and Biomolecular Engineering Korea Advanced Institute of Science and Technology(KAIST)Daejeon 34141Republic of Korea Department of Chemical and Biomolecular Engineering Yonsei UniversitySeoul 03722Republic of Korea Department of Chemical and Biomolecular Engineering Sogang UniversitySeoul 04107Republic of Korea

Organic electrolyte-gated transistors(OEGTs) have the benefits of low power consumption and large current ***,the electrical performance of n-type OEGTs lags far behind that of p-type *** this study,we design a series of polymers,P(NDITEG-T) and P(NDIMTEG-T),comprising a naphthalene diimide backbone for n-type charge transport and oligo(ethylene glycol)(OEG) side chains for high ionic conductivity and eco-friendly solution *** incorporation of the OEG chain facilitates the electrochemical doping of the semiconductor by ions to realize high-performance,n-type ***,in OEGTs,P(NDITEG-T) achieves a high electron mobility of 1.0 × 10^(-1) cm^(2) V^(-1) s^(-1),which represents the highest value reported for solution-processed,n-type *** is noted that the fabrication of the OEGTs is achieved by solution processing with eco-friendly ethanol/water mixtures in virtue of the hydrophilic OEG *** work demonstrates the molecular design of the P(NDITEG-T) polymer and its significant ability to produce aqueous-processable,high-performance,and n-type OEGTs.

关键词： organic electrolyte-gated transistors n-type transistors oligo(ethylene glycol)polymers eco-friendly solution process high electron mobility

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Difference in the Hot Compressive Behavior and Processing Maps between the As-cast and Homogenized Al-Zn-Mg-Cu(7075) Alloys

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journal of Materials Science & Technology 2016年第7期32卷 660-670页

作者： S.Y. Park W.j. kim Department of Materials Science and Engineering Hongik University 72-1 Sangsu-dong Mapo-gu Seoul 121-791 Republic of Korea Advanced Fusion Process R&D Group Korea Institute of Industrial Technology 994-32 Dongchun-dong Yeonsu-gu Incheon 406-130 Republic of Korea

The deformation mechanisms and processing maps of the as-cast Al-Zn-Mg-Cu （？0？5） aluminum （AI） alloy were studied and compared with those of the homogenized 7075 Al alloy in the temperature range of 573-723 k and in the strain rate range of 10 3-10 s-1 to explore a possibility for directly using the as- cast 7075 Al alloy as a billet for hot working. The as-cast and homogenized 7075 A1 alloys had similar grain sizes and showed similar high-temperature deformation behaviors. The as-cast 7075 Al alloy, however, exhibited higher power efficiencies and smaller unstable flow regions compared to the homogenized 7075 AI alloy because of the presence of secondary phases （MgZn2） segregated at the dendritic interfaces in the as-cast microstructure, which were formed during non-equilibrium solidification. These segregated phases provided nucleation sites for dynamic recovery or continuous dynamic recrystallization, and as a result a fine and more homogeneous （sub）grain structure could be obtained from the as-cast micro- structure compared to the homogenized microstructure. The current work suggested the possibility and advantage of using as-cast microstructures for hot working of aluminum alloys with high content of solutes.

关键词： Al-based alloysProcessing mapHot compressionAs-cast microstructureSegregationRecrystallization

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The hot compressive deformation behavior of cast Mg-Gd-Y-Zn-Zr alloys with and without LPSO phase in their initial microstructures

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journal of Magnesium and Alloys 2022年第10期10卷 2901-2917页

作者： H.T.jeong W.j.kim Departmentof Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul 121-791Republic of Korea

Samples of Mg-8.2Gd-3.8Y-1.1Zn-0.4Zr alloy with and without an intragranular lamellae-shaped long period stacking ordered(LPSO)phase were prepared through heat treatment and a series of hot compression tests on these materials were conducted to examine and evaluate the influence of LPSO on the hot compressive deformation behavior and deformation mechanisms at a given alloy *** values of activation energy for plastic flow(Qc)of the solution treated(without LPSO phase)and annealed alloys(with intragranular LPSO phase)were larger than that for pure Mg,indicating that the presence of a high amount of rare earth(RE)elements and LPSO in the Mg matrix significantly increases *** Qcvalue of the annealed alloy was larger than that of the solution treated alloy at all the strain levels(223.3 vs.195.5 k j/mol in average)and the largest difference in Qcbetween the two alloys was recorded at the smallest strain of 0.1 where precipitation of LPSO during deformation was limited in the solution treated *** observations imply that the formation of LPSO phase out of the RE-rich solid solution matrix during deformation increases Qc,but the increment is not so *** of the hot compressive data of the alloys with LPSO phase and the alloys with RE-rich solid solution matrix in literatures indicates the similarity of the effect of the LPSO and RE-rich solid solution matrix phases on Qcand high-temperature strength.

关键词： Magnesium alloys LPSO Deformation mechanism Dynamic recrystallization Activation energy for plastic flow Processing maps

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