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Dynamic deformation behavior and microstructural evolution during high-speed rolling of Mg alloy having non-basal texture

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Journal of Materials Science & Technology 2019年第4期35卷 473-482页

作者： Sang-Hoon Kim Jeong Hun lee chong soo lee Jonghun Yoon Sung Hyuk Park School of Materials Science and Engineering Kyungpook National University Ulsan Regional Division Korea Institute of Industrial Technology Graduate Institute of Ferrous Technology Pohang University of Science and Technology Department of Mechanical Engineering Hanyang University

The dynamic deformation behaviors and resultant microstructural variations during high-speed rolling(HSR) of a Mg alloy with a non-basal texture are investigated. To this end, AZ31 alloy samples in which the basal poles of most grains are predominantly aligned parallel to the transverse direction(TD) are subjected to hot rolling with different reductions at a rolling speed of 470 m/min. The initial grains with a TD texture are favorable for {10–12} twinning under compression along the normal direction(ND); as a result, {10–12} twins are extensively formed in the material during HSR, and this consequently results in a drastic evolution of texture from the TD texture to the ND texture and a reduction in the grain size. After the initial grains are completely twinned by the {10–12} twinning mechanism, {10–11} contraction twins and {10–11}-{10–12} double twins are formed in the {10–12} twinned grains by further *** the contraction twins and double twins have crystallographic orientations that are favorable for basal slip during HSR, dislocations easily accumulate in these twins and fine recrystallized grains nucleate in the twins to reduce the increased internal strain energy. Until a rolling reduction of 20%, {10–12}twinning is the main mechanism governing the microstructural change during HSR, and subsequently,the microstructural evolution is dominated by the formation of contraction twins and double twins and the dynamic recrystallization in these twins. With an increase in the rolling reduction, the average grain size and internal strain energy of the high-speed-rolled(HSRed) samples decrease and the basal texture evolves from the TD texture to the ND texture more effectively. As a result, the 80% HSRed sample, which is subjected to a large strain at a high strain rate in a single rolling pass, exhibits a fully recrystallized microstructure consisting of equiaxed fine grains and has an ND basal texture without a TD texture component.

关键词： Magnesium alloy High-speed rolling Texture Dynamic recrystallization Twinning

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Dynamic recrystallization behavior and microstructural evolution of Mg alloy AZ31 through high-speed rolling

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Journal of Materials Science & Technology 2018年第10期34卷 1747-1755页

作者： Jeong Hun lee Jong Un lee Sang-Hoon Kim Seok Weon Song chong soo lee Sung Hyuk Park Ulsan Regional Division Korea Institute of Industrial Technology School of Materials Science and Engineering Kyungpook National University Technical Research Laboratories POSCO Graduate Institute of Ferrous Technology Pohang University of Science and Technology

High-speed rolling （HSR） is known to improve the workability of Mg alloys significantly, which makes it possible to impose a large reduction in a single pass without fracture. In the present study, dynamic recrystallization （DRX） behavior and microstructural and textural variations of Mg alloy AZ31 dur-ing a HSR process were investigated by conducting rolling with different imposed reductions in the range of 20%-80% at a high rolling speed of 470 m/min and 400℃. High-strain-rate deformation during HSR suppresses dislocation slips but promotes twinning, which results in the formation of numer-ous twins of several types, i.e., {10-12} extension twins, {10-11} and {10-13} contraction twins, and {10-11}-{10-12} double twins. After twinning, high strain energy is accumulated in twin bands because their crystallographic orientations are favorable for basal slips, leading to subsequent DRX at the twin bands. Accordingly, twinning activation and twinning-induced DRX behavior play crucial roles in accommodating plastic deformation during HSR and in varying microstructure and texture of the high- speed-rolled （HSRed） sheets. Area fraction of fine DRXed grains formed at the twin bands increases with increasing rolling reduction, which is attributed to the combined effects of increased strain, strain rate, and deformation temperature and a decreased critical strain for DRX. Size, internal strain, and texture intensity of the DRXed grains are smaller than those of unDRXed grains. Therefore, as rolling reduction increases, average grain size, stored internal energy, microstructural inhomogeneity, and basal texture intensity of the HSRed sheets gradually decrease owing to an increase in the area fraction of the DRXed grains.

关键词： Magnesium alloy High-speed rolling Twinning Dynamic recrystallization 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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Comparative study of tensile and high-cycle fatigue properties of extruded AZ91 and AZ91-0.3Ca-0.2Y alloys

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Journal of Materials Science & Technology 2021年第34期93卷 41-52页

作者： Ye Jin Kim Young Min Kim Seong-Gu Hong Dae Woong Kim chong soo lee Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea Implementation Research Division Korea Institute of Materials ScienceChangwon 51508Republic of Korea Division of Industrial Metrology Korea Research Institute of Standards and ScienceDaejeon 34113Republic of Korea Energy Infra Material Measure Team Korea Research Institute of Standards and ScienceDaejeon 34113Republic of Korea Graduate Institute of Ferrous Technology Pohang University of Science and Technology.Pohang 37673Republic of Korea

Mg-Al-Zn-Ca-Y alloys with excellent ignition and corrosion resistances—termed SEN alloys(where the letters"S,""E,"and"N"stand for stainless,environmentally friendly,and non-flammable,respectively)—have been developed *** this study,the microstructure,tensile properties,and high-cycle fatigue properties of an extruded Mg-9.0Al-0.8Zn-0.1Mn-0.3Ca-0.2Y(SEN9)alloy are investigated and compared with those of a commercial Mg-9.0Al-0.8Zn-0.1Mn(AZ91)alloy extruded under the same *** the extruded SEN9 alloy and the extruded AZ91 alloy have a fully recrystallized structure comprising equiaxed grains,but the former has a smaller average grain size owing to the promoted dynamic recrystallization during *** extruded AZ91 alloy contains coarse Mg_(17)Al_(12) discontinuous precipitate(DP)bands parallel to the extrusion direction,which are formed during its cool down after *** contrast,the extruded SEN9 alloy contains relatively fine undissolved Al_(2)Ca,Al_(8)Mn_(4)Y,and Al_(2)Y second-phase particles,which are formed during the solidification stage of the casting *** tensile strength of the extruded SEN9 alloy,which has finer grains and more abundant particles,is slightly higher than that of the extruded AZ91 ***,the difference in their strengths is relatively small because the stronger solid-solution hardening and precipitation hardening effects in the extruded AZ91alloy offset the stronger grain-boundary hardening and dispersion hardening effects in the extruded SEN9alloy to some *** tensile elongation of the extruded AZ91 alloy is significantly lower than that of the extruded SEN9 alloy because the large cracks formed in the DP bands in the former cause its premature *** the extruded SEN9 alloy has higher tensile properties than the extruded AZ91alloy,the high-cycle fatigue life and fatigue strength of the former are shorter and lower,respectively,than those of the *** DP bands in the extruded

关键词： Mg-Al-Zn-Ca-Y alloy Extrusion Tensile properties High-cycle fatigue Crack source

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A review of the effect of tungsten alloying on the microstructure and properties of steels

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Tungsten 2023年第4期5卷 440-466页

作者： Jun-Jie Lian Xiao-Guang Ma Zheng-Yi Jiang chong soo lee Jing-Wei Zhao College of Mechanical and Vehicle Engineering Taiyuan University of TechnologyTaiyuan030024China Engineering Research Center of Advanced Metal Composites Forming Technology and Equipment Ministry of EducationTaiyuan030024China Taiyuan University of Technology-University of Wollongong(TYUT-UOW)Joint Research Center Taiyuan University of TechnologyTaiyuan030024China School of Mechanical MaterialsBiomedical and Mechatronic EngineeringUniversity of WollongongWollongongNSW2522Australia TYUT‑UOW Joint Research Center University of WollongongWollongongNSW2522Australia Graduate Institute of Ferrous and Energy Materials Technology Pohang University of Science and TechnologyPohang37673South Korea

With the continuous development of science and technology,the increasingly severe service environment makes people put forward higher requirements for the performance of alloy *** has unique properties such as excellent strength,high density and good hardness,and its addition as an alloying element will change the properties of alloy *** paper aims to summarize the effect of the addition of tungsten on the micro structure and mechanical properties of alloy *** background of research and application of tungsten alloyed steel is presented ***,the preparation methods of tungsten alloyed steel are ***,the effect of tungsten incorporation on the microstructure of alloy steel is ***,the effects of tungsten addition on the mechanical properties,corrosion resistance and hydrogen embrittlement resistance of the alloy steel are *** review provides an outlook on the development of tungsten alloyed steel,which will stimulate more in-depth research and ultimately promote the practical application of tungsten alloyed steel.

关键词： Tungsten Alloy steel Microstructure Properties

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基于温度场模拟的铸件表面硼化物梯度耐磨材料成形机制

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农业工程学报 2011年第8期27卷 184-188页

作者：宋月鹏柳洪洁李学超 Hyoug-Soep Kim chong-soo lee 山东农业大学机械与电子工程学院泰安271018 浦项工科大学材料科学与工程学院山东省园艺机械与装备重点实验室泰安271018 山东农业大学动物科技学院泰安271018

利用ANSYS10.0,对铸件表面硼化物梯度耐磨材料成形过程中温度场进行了模拟验证,对梯度耐磨材料不同部位的成形机制进行了分析研究,结果表明,模拟结果与试验结果较为吻合,合金粉块不同部位温度变化将影响复合材料的质量,内层及中间层温度... 详细信息

利用ANSYS10.0,对铸件表面硼化物梯度耐磨材料成形过程中温度场进行了模拟验证,对梯度耐磨材料不同部位的成形机制进行了分析研究,结果表明,模拟结果与试验结果较为吻合,合金粉块不同部位温度变化将影响复合材料的质量,内层及中间层温度高,高温持续时间长,熔合质量好,而对于最外层,温度较低(<1000℃),高温持续时间短,尖角处温降快,导致这些部位复合材料熔合质量较差、缺陷较多。进一步研究表明,砂型材料的导热率及合金粉块内低熔点的熔合剂过多均会影响复合材料的质量。

关键词：合金表面合金化梯度耐磨材料硼化物温度场计算机模拟

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Inhomogeneous Hardness Distribution of High Pressure Torsion Processed IF Steel Disks

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Materials Sciences and Applications 2012年第4期3卷 234-239页

作者： Yuepeng Song Wenke Wang Dongsheng Gao Hyoung-Seop Kim Eun-Yoo Yoon Dong-Jun lee chong-soo lee Jing Guo Department of Materials Sci- ence and Engineering Pohang University of Science and Technology Pohang Korea Department of Materials Science and Engineering Pohang University of Science and Technology Pohang Korea Mechanical and Electronic Engineering College Shandong Agricultural University Tai’an China Shandong Provincial Key Laboratory of Horticultural Machineries and Equipments Shandong Agricultural University Tai’an China.

The inhomogeneous hardness distribution of high pressure torsion (HPT) processed IF steel disks along different directions is investigated. The results indicated that there exists inhomogeneous distribution in HPT processed IF steel disks, giving lower hardness in the center and higher hardness in the edge regions. However, on the axisymmetrical section testing plane of the disks’ thickness direction, there is a soft zone near the surface of disks. Further results from radius testing plane of different depths from the surface of HPT processed disks show that the inhomogeneity rules of hardness distribution on the radius direction are similar to that on the thickness direction. Compared with the initial state, different stages of HPT (compression and compression + torsion) can both remarkably increase the hardness of IF steel disks. Microstructure investigation results can give a well support to verify the rules of hardness distribution, showing hardly no change of grains in center and sever plastic deformation in edge. The inhomogeneous distribution of stress and strain with the huge friction between anvil and disks in the process of HPT play an important role of hardness and microstructure distribution.

关键词： Hardness Distribution High-Pressure Torsion (HPT) IF Steel Inhomogeneous

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Fabrication of Silicon Carbide Quantum Dots via Chemical-Etching Approach and Fluorescent Imaging for Living Cells

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Materials Sciences and Applications 2014年第4期5卷 177-182页

作者： Yuepeng Song Dongsheng Gao Hyoung Seop Kim Cuiqin Qu Jie Kang Yanmin Zhu Ziping Liu Jing Guo Lingfeng Xu chong soo lee College of Horticulture Science and Engineering Shandong Agricultural University Tai’an China Department of Materials Science and Engineering Pohang University of Science and Technology Pohang Korea Shandong Provincial Key Laboratory of Horticultural Machineries and Equipments Mechanical and Electronic Engineering College Shandong Agricultural University Tai’an China Shandong Provincial Key Laboratory of Horticultural Machineries and Equipments Mechanical and Electronic Engineering College Shandong Agricultural University Tai’an China College of Horticulture Science and Engineering Shandong Agricultural University Tai’an China Department of Materials Science and Engineering Pohang University of Science and Technology Pohang Korea Shandong Provincial Key Laboratory of Horticultural Machineries and Equipments Mechanical and Electronic Engineering College Shandong Agricultural University Tai’an China Department of Materials Science and Engineering Pohang University of Science and Technology Pohang Korea State Grid of China Technology College Tai’an China

A simple chemical-etching approach is used to prepare the silicon carbide quantum dots (QDs). The raw materials of silicon carbide (SiC) with homogeneous nanoparticles fabricated via self-propagating combustion synthesis are corroded in mixture etchants of nitric and hydrofluoric acid. After sonication and chromatography in the ultra-gravity field for the etched products, aqueous solution with QDs can be obtained. The microstructure evolution of raw particles and optical properties of QDs were measured. Different organophilic groups on the surface like carboxyl, oxygroup, and hyfroxy were produced in the process of etching. Fluorescent labeling and imaging for living cells of Aureobasidium pulluans were investigated. The results indicated that SiC QDs were not cytotoxic and could stably label due to the conjugation between organophilic groups of QDs and specific protein of cells, it can be utilized for fluorescent imaging and tracking cells with in vivo and long-term-distance. Moreover, mechanism and specificity of mark were also analyzed.

关键词： Silicon Carbide Quantum Dots (QDs) Fluorescent Imaging Living Cells Aureobasidium pulluans

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Changes and development plans in the mountain villages of South Korea:Comparison of the first and second national surveys

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Journal of Mountain Science 2017年第8期14卷 1473-1489页

作者： Hag Mo KANG Hyun KIM Chang Heon lee chong Kyu lee soo Im CHOI Department of Forest Environmental Science Chonbuk National University Jeollabuk-do Forest Environment Research Institute Department of Forest Resources Gyeongnam National University of Science and Technology Department of Forest Resources Sunchon National University

Owing to the geographic disadvantages of mountain villages, the social, cultural, and economic conditions of mountain villagers are inferior to those of urban dwellers in South Korea. Thus, in 1995, the The government of South Korea launched a mountain village development support program to promote agriculture and forestry, balance national land development, and preserve cultural heritage. The program was effectively implemented, improving the income, population size, and living conditions of villagers in addition to setting up a system for stable project implementation. However, concerns were raised about long-term development planning, the creation and marketing of specialty brands, facility management/operation, and follow-up support. The government conducted surveys of mountain villagers in 2003 and 2014, obtaining basic data to address these issues. This study evaluates the outcomes of these two surveys, suggesting areas requiring focusedaction, concentrating on village development projects, forest resource distribution and use, demographic trends, the economy, exchange with urban areas, green tourism, and master planning. We find that despite growth in the forest labor force, forest ownership is diminishing in terms of the number and scale of holdings. Consequently, it is necessary to commercialize forest resources, establish favorable settlement conditions, and expand government support for village-run projects. In addition, systematic forest management for older tree age classes would benefit the public and provide assets for future mountain village development. Our results are expected to provide baseline information for the establishment and efficient implementation of mountain village development policy.

关键词： Forest resources management Mountain village changes Mountain village economy Support for mountain villages Urban-rural exchange

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Velocity Profiles between Two Baffles in a Shell and Tube Heat Exchanger

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Journal of Thermal Science 2015年第4期24卷 356-363页

作者： Tae-Hyun Chang Chang-Hoan lee Hae-soo lee Kwon-soo lee Senior Research Fellow of RESEAT Korea Institute of Science and Technology Information Korea Institute of Science and Technology Information Postdoctoral Research Fellow School of Mechanical Engineering of Kyungnam University International University of Korea

Heat exchangers are extensively utilized for waste heat recovery,oil refining,chemical processing,and steam *** this study,velocity profiles are measured using a 3D particle image velocimetry(PIV)system between two baffles in a shell and tube heat exchanger for parallel and counter *** PIV and computational fluid dynamics results show the occurrence of some strong vectors near the *** vectors are assumed due to the clearance between the inner tubes and the front ***,the major parts of the vectors are moved out through the bottom opening of the rear baffle,and other vectors produce a large circle between the two *** simulations are conducted to investigate the effects of the baffle on the heat exchanger using the Fluent *** k-εturbulence model is employed to calculate the flows along the heat exchanger.

关键词： Baffle P1V Shell and tube heat exchanger Cut off ratio CFD

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