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Critical review of superplastic magnesium alloys with emphasis on tensile elongation behavior and deformation mechanisms

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journal of Magnesium and Alloys 2022年第5期10卷 1133-1153页

作者： H.T.jeong W.j.kim Department of Materials Science and Engineering Hongik UniversitySangsu-dong 72-1 Mapo-guSeoul 121-791South Korea

The tensile elongation behavior and deformation mechanisms of superplastic Mg alloys and Mg composites were examined by extensively reviewing the literature published from the time of the first report on the superplasticity of Mg alloys to the present *** on the superplasticity of Mg alloys have been conducted mainly on Mg-Al-Zn(AZ)series alloys,Mg-Zn-Zr(Zk),Mg-Li and Mg-RE(rare earth)alloys,and in recent years,Mg-RE alloys have attracted the greatest *** effect of grain size and the type and amount of secondary phase particles on the superplasticity of Mg alloys was systematically examined and *** alloys processed by severe plastic deformation(SPD)and powder-metallurgy methods have smaller grain sizes and exhibit superior superplasticity compared to conventionally processed(by extrusion and rolling)Mg *** the AZ alloys,as the volume fraction of the Mg17Al12phase increases,smaller grains are obtained,and the low-temperature superplasticity(LTS)and high-strain-rate superplasticity(HSRS)characteristics become *** Zk60 alloy with finely dispersed Mg Zn2particles exhibits excellent LTS,while the Mg-RE alloys with a high fraction of thermally stable particles exhibit excellent ***-Li alloys can exhibit LTS even at room temperature due to the presence of a high-volume fraction of the body centered cubic(BCC)phase where atomic diffusivity is *** boundary diffusion-and lattice diffusion-controlled grain boundary sliding are found to operate as the dominant deformation mechanisms below~473 k and above~673 k,respectively,at small grain *** mechanism maps were constructed based on the analysis of the deformation behavior of superplastic Mg alloys,and from the maps,the critical conditions for achieving LTS,HSRS and simultaneous achievement of LTS and HRSR were calculated and proposed,and their importance was discussed.

关键词： Magnesium alloys Superplastic Grain size Secondary phase Grain boundary sliding

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Superplastic behavior of an ultrafine-grained Mg-13Zn-1.55Y alloy with a high volume fraction of icosahedral phases prepared by high-ratio differential speed rolling

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journal of Materials Science & Technology 2017年第9期33卷 919-925页

作者： T.Y.kwak W.j.kim Rare Metal R&BD Group Korea Institute of Industrial Technology Department of Materials Science and Engineering Hongik University

An ultrafine-grained（UFG） Mg-13Zn-1.55 Y alloy（ZW132） with a high volume fraction（7.4%） of icosahedral phase（I-phase, Mg;Zn;Y） particles was prepared by applying high-ratio differential speed rolling（HRDSR） on the cast microstructure following homogenization. The alloy exhibited excellent superplasticity at low temperatures(tensile elongations of 455% and 1021% 473 k-10;s;and 523 k-10;s;,respectively). Compared with UFG Mg-9.25Zn-1.66 Y alloy（ZW92） with a lower volume fraction of I-phase particles（4.1%）, which was prepared using the same processing routes, the UFG ZW132 alloy exhibited a higher thermal stability of grain size. Rapid grain coarsening, however, occurred at temperatures beyond523 k, leading to a loss of superplasticity. The high-temperature deformation behavior of the HRDSRprocessed ZW132 alloy could be well described assuming that the mechanisms of grain boundary sliding and dislocation climb creep competed with each other and considering that the grain-size was largely increased by accelerated grain growth at the temperatures beyond 523 k.

关键词： Magnesium alloy Superplastic deformation Ultrafine grain Icosahedral quasicrystal Grain growth

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Effect of refinement of grains and icosahedral phase on hot compressive deformation and processing maps of Mg-Zn-Y magnesium alloys with different volume fractions of icosahedral phase

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journal of Materials Science & Technology 2019年第1期35卷 181-191页

作者： T.Y.kwak W.j.kim Department of Materials Science and Engineering Hongik University

The effect of the volume fraction of I-phase on the hot compressive behavior and processing maps of the extruded Mg-Zn-Y alloys was examined, and the obtained results were compared with those of the cast alloys in a previous work. The average grain sizes, fractions of dynamically recrystallized(DRXed) grains,and sizes of DRXed grains of the extruded alloys after compressive deformation were significantly smaller,higher and smaller, respectively, than those of the cast alloys after compressive deformation under the same experimental conditions. This was because the microstructures of the extruded alloys, having much more grain boundaries and more refined I-phase particles than the cast alloys, provided a larger number of nucleation sites for dynamic recrystallization than those of the cast alloys. The constitutive equations for high-temperature deformation of the extruded and cast alloys could be derived using the same activation energy for plastic flow, which was close to the activation energy for lattice diffusion in *** with the cast alloys, the onset of the power law breakdown(PLB) occurred at larger ZenerHolloman(Z) parameter values in the extruded alloys. This was because the extruded alloys had finer initial grain sizes and higher fractions of finer DRXed grains compared to the cast alloys, such that the onset of PLB caused by creation of excessive concentrations of deformation-induced vacancies was delayed to a higher strain rate and a lower temperature. The flow-stress difference between the extruded alloys and the cast alloys could be attributed to the difference in the fraction of DRXed grains. According to the processing maps, the extruded alloys exhibited higher power dissipation efficiency and flow stability than the cast alloys. This agreed with the microstructural observations.

关键词： Hot compression Magnesium alloy Processing map Grain refinement Dynamic recrystallization

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New para-magnetic(CoFeNi)(50)(CrMo)(50-x)(CB)x(x=20,25,30)non-equiatomic high entropy metallic glasses with wide supercooled liquid region and excellent mechanical properties

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journal of Materials Science & Technology 2020年第8期36卷 135-143页

作者： jeong Tae kim Sung Hwan Hong jin Man Park jürgen Eckert ki Buem kim Erich Schmid Institute of Materials Science Austrian Academy of Sciences(ÖAW)Jahnstrae 128700LeobenAustria Hybrid Materials Center(HMC) Department of Nanotechnology and Advanced Materials EngineeringSejong University209Neungdong-roGwangjin-guSeoul143-747Republic of Korea Global Technology Center(GTC) Samsung Electronics Co.Ltd129 Samsung-roYeongtong-guSuwonsiGyeonggi-do443-742Republic of Korea Department of Materials Science Chair of Materials PhysicsMontanuniversität LeobenJahnstraße 128700LeobenAustria

In this study,high entropy metallic glasses(HEMGs)were developed through a combination of concepts for designing metallic glasses(main element+transition metal+metalloid element)and high-entropy alloys(more than five elements,each element having an atomic concentration between 5 at.%and 35 at.%).The developed metallic glass alloys are composed of Co-Fe-Ni main elements,transition metals(Cr,Mo)and metalloid elements(C,B).Moreover,the present work reports the thermal,mechanical and magnetic properties of(CoFeNi)(50)(CrMo)(50-x)(CB)x alloys with x=20,25,*** developed as-spun HEMGs exhibit typical paramagnetic properties even for a high amount of ferromagnetic elements(Co,Fe,and Ni)and have high elastic modulus(103–160 GPa)and hardness(14–27 GPa),thus possessing mechanical properties similar to well-known Co-based metallic glasses(Co-Cr-Mo-C-B system).In addition,some of the bulk samples prepared with a diameter of 2 mm form bulk metallic glasses with a high compressive strength around 3.5 *** mechanisms determining the stability of the supercooled liquid,as well as the paramagnetic and mechanical properties for the developed non-equiatomic HEMGs,are discussed.

关键词： Metallic glasses Paramagnetism High entropy alloys Phase stability

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Mg-Al Alloys Manufactured by Casting and Hot Working Process

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journal of Materials Science & Technology 2008年第1期24卷 96-98页

作者： j.M.kim j.H.jun W.j.jung Department of Applied Materials Eng. Hanbat National University Daejeon 305-719 Korea Light Materials Team Korea Institute of Industrial Technology Incheon 406-800 Korea

Mechanical properties of Mg-Al based alloys at different fabrication state,namely as-cast,hot rolled,and annealed,were investigated to develop the alloys that are suitable for the casting/hot working ***- imental results indicated that the castability such as hot cracking resistance tends to improve with increasing the aluminum ***,the elongation at elevated temperatures was observed to decrease as the AI content increases,implying difficulties in hot forming.A small amount of Zr additions could significantly enhance the room temperature mechanical properties of hot-rolled Mg-6%Al-1%Zn *** tendency of remarkable grain coarsening at high temperatures was effectively reduced by the Zr *** analyses suggested that very fine Al-3Zr precipitates formed in the Zr-added alloy are responsible for the obtained results.

关键词： Magnesium Casting Forming Tensile properties

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Applying robust design to study the effects of stratigraphic characteristics on brittle failure and bump potential in a coal mine

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International journal of Mining Science and Technology 2018年第1期28卷 137-144页

作者： Bo-Hyun kim Mark k.Larson Heather E.Lawson Spokane Mining Research Division NIOSH/CDC

Bumps and other types of dynamic failure have been a persistent, worldwide problem in the underground coal mining industry, spanning *** example, in just five states in the *** 1983 to 2014,there were 388 reportable *** significant advances in mine design tools and mining practices,these events continue to *** conditions have been associated with bump potential, such as the presence of stiff units in the local *** effect of a stiff sandstone unit on the potential for coal bumps depends on the location of the stiff unit in the stratigraphic column, the relative stiffness and strength of other structural members, and stress concentrations caused by *** study describes the results of a robust design to consider the impact of different lithologic risk factors impacting dynamic failure *** the inherent variability of stratigraphic characteristics in sedimentary formations,such as thickness, engineering material properties, and location, is significant and the number of influential parameters in determining a parametric study is large, it is impractical to consider every simulation case by varying each parameter ***, to save time and honor the statistical distributions of the parameters, it is necessary to develop a robust design to collect sufficient sample data and develop a statistical analysis method to draw accurate conclusions from the collected *** this study,orthogonal arrays, which were developed using the robust design, are used to define the combination of the(a) thickness of a stiff sandstone inserted on the top and bottom of a coal seam in a massive shale mine roof and floor,(b) location of the stiff sandstone inserted on the top and bottom of the coal seam,and(c) material properties of the stiff sandstone and contacts as interfaces using the 3-dimensional numerical model, *** completion of the numerical experiments, statistical and multivariate analysis are performed using

关键词： Bumps Robust design FLAC3D Plastic dissipated energy Multiple regression

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Mending the broken in amyotrophic lateral sclerosis: DNA damage and repair in motor neuron degeneration

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Neural Regeneration Research 2021年第1期16卷 104-105页

作者： Byung Woo kim Lee j.Martin Department of Pathology Division of Neuropathologythe Pathobiology Graduate Training ProgramJohns Hopkins University School of MedicineBaltimoreMDUSA Department of Neuroscience Johns Hopkins University School of MedicineBaltimoreMDUSA

Amyotrophic lateral sclerosis(ALS)is a fatal neurodegenerative disease that causes paralysis and respiratory failure(Petrov et al.,2017).The driving mechanisms are unknown,and there are no effective treatments(Petrov et al.,2017).Aging and a few gene mutations,a common one being missense mutations in superoxide dismutase-1(SOD1),are risk factors for ALS(Figure 1).The recent Food and Drug Administration approval of edaravone for the treatment of ALS putatively supports a role for oxidative and nitrative stresses in the disease processes(Figure 1A).DNA damage,abnormalities in DNA repair,and other nuclear abnormalities are implicated also in the pathogenesis of human ALS(Bradley and krasin,1982;kim et al.,2020).

关键词： al. damage degeneration

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The Gas-to-Dust Relation in the Dark Cloud L1523-Observational Evidence for CO Gas Depletion

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Chinese journal of Astronomy and Astrophysics 2008年第6期8卷 686-692页

作者： H.G.kim B.G.kim j.H.jung korea Astronomy and Space Science Institute 61-1 Hwaam Yuseong Daejeon 305-348 Korea

Correlation between gas and dust column density has been studied for the dark globule L1523. The 13CO（j=1→0） emission is used for tracing the gas, and the IR emissions, for tracing the dust constituent. In order to match the beam resolution between the images, a beam de-convolution algorithm based on the Maximum Correlation Method （MCM） was applied on the Infrared Astronomical Satellite （IRAS） data. The morphology of 13CO column density map shows a close correlation to that of 100μm dust optical depth. The distribution of the optical depth at 100 μm follows that of gas column density more closely than does the flux map at either 60 or 100μm. The ratio of the 13CO column density to the 100μm optical depth shows a decreasing trend with increasing dust optical depth in the central part, indicating possible molecular gas condensation onto dust particles. The excessive decrease in the CO column density in the envelope may most probably be due to the photo-dissociation of CO molecules.

关键词： ISM: clouds ISM: dust ISM: molecules

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Magnetic force improvement and parameter optimization for magnetic abrasive polishing of AZ31 magnesium alloy

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中国有色金属学会会刊：英文版 2008年第A01期18卷 369-373页

作者： S.O.kim j.S.kWAk Graduate School of Mechanical Engineering Pukyong National UniversitySouth Korea School of Mechanical Engineering Pukyong National UniversitySouth Korea

The magnetic force acting on workpiece to be machined plays a significantly important role in magnetic abrasive polishing *** in a case of polishing nonferrous materials,the strength of magnetic force is very low and it leads lower polishing *** magnesium alloy that has superior mechanical properties for industrial application such as a lightweight and high specific strength is one of the most famous nonferrous *** improving strategy of the magnetic force for the AZ31 magnesium alloy installed with a permanent magnet was proposed and experimental verification was carried *** the proposed strategy,the effect of process parameters on the surface roughness of the AZ31 magnesium alloy was evaluated by a design of experimental method.

关键词：镁合金物理性能磁力最优化设计磁性

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Benefits of Stochastic Optimization for Scheduling Energy Storage in Wholesale Electricity Markets

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journal of Modern Power Systems and Clean Energy 2021年第1期9卷 181-189页

作者： Hyeong jun kim Ramteen Sioshansi Antonio j.Conejo the Department of Integrated Systems Engineering The Ohio State UniversityColumbusOhioUSA the Department of Electrical and Computer Engineering The Ohio State UniversityColumbus.OhioUSA

We propose a two-stage stochastic model for optimizing the operation of energy storage. The model captures two important features: uncertain real-time prices when day-ahead operational commitments are made;and the price impact of charging and discharging energy storage. We demonstrate that if energy storage has full flexibility to make real-time adjustments to its day-ahead commitment and market prices do not respond to charging and discharging decisions, there is no value in using a stochastic modeling framework, i.e., the value of stochastic solution is always zero. This is because in such a case the energy storage behaves purely as a financial arbitrageur day ahead, which can be captured using a deterministic *** show also that prices responding to its operation can make it profitable for energy storage to "waste" energy, for instance by charging and discharging simultaneously, which is normally sub-optimal. We demonstrate our model and how to calibrate the price-response functions from historical data with a practical case study.

关键词： Energy storage stochastic optimization value of stochastic solution electricity market

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