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Journal of Magnesium and Alloys 2023年第6期11卷 2165-2181页

作者： gyo myeong lee Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea

Effects of Gd addition on the strain hardening behavior and yield asymmetry of pure Mg are investigated by subjecting extruded pure Mg,Mg–5Gd,and Mg–15Gd(all in wt%)to tension and compression tests along the extrusion direction(ED).As the amount of Gd added to pure Mg increases,the basal texture tilts toward the ED and the distribution of c-axes of grains becomes *** tension,the strain hardening rates of all the materials decrease until ***,under compression,the strain hardening rate increases in the early stage of deformation in pure Mg and Mg–5Gd,whereas it continuously decreases in Mg–*** Mg exhibits considerably high tension-compression yield asymmetry,with a compressive yield strength(CYS)to tensile yield strength(TYS)ratio of *** contrast,Mg–5Gd exhibits excellent yield symmetry with CYS/TYS of 0.9 and Mg–15Gd exhibits reversed yield asymmetry with CYS/TYS of *** mechanisms of these drastically different Gd-addition-induced deformation behaviors of the materials are discussed in terms of the crystallographic distribution of grains and the relative activation stresses of basal slip,prismatic slip,pyramidal slip,and{10–12}twinning under tension and compression.

关键词： Pure Mg Gd addition Texture Yield asymmetry Activation stress

Difference in extrusion temperature dependences of microstructure and mechanical properties between extruded AZ61 and AZ91 alloys

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Journal of Magnesium and Alloys 2023年第5期11卷 1683-1696页

作者： Dong Hee lee gyo myeong lee Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea

The effects of extrusion temperature on the microstructure and tensile properties of extruded AZ61 and AZ91 alloys are investigated by subjecting them to hot extrusion at 300 and 400℃.Although the average grain size of the extruded AZ61 alloy slightly increases from 9.5 to 12.6μm with increasing extrusion temperature,its resultant microstructural variation is *** contrast,the average grain size of the extruded AZ91 alloy significantly increases from 5.7 to 22.5μm with increasing extrusion temperature,and the type of Mg17Al12 precipitates formed in it changes from fine dynamic precipitates with a spherical shape to coarse static precipitates with a lamellar *** the extrusion temperature increases,the tensile yield strength of the extruded AZ61 alloy increases from 183 to 197 MPa while that of the extruded AZ91 alloy decreases from 232 to 224 *** tensile elongations of the extruded AZ61 and AZ91 alloys decrease with increasing extrusion temperature,but the degree of decrease is significant in the latter *** different extrusion temperature dependences of the tensile properties of the extruded AZ61 and AZ91 alloys are discussed in terms of their microstructural characteristics,strengthening mechanisms,and crack initiation sites.

关键词： Mg-Al-Zn alloys Extrusion temperature Precipitation Strengthening mechanism Tensile properties

Effects of surface roughness on bending properties of rolled AZ31 alloy

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Journal of Magnesium and Alloys 2023年第4期11卷 1224-1235页

作者： gyo myeong lee Jong Un lee Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea

This study investigated the effects of mechanical-polishing-induced surface roughness and the direction of polishing lines on the bending properties of a rolled AZ31 *** this end,three-point bending tests were performed on one sample without polishing lines(SS sample)and two samples with polishing lines—one in which the polishing lines were parallel to the rolling direction(RS-RD sample)and the other in which they were parallel to the transverse direction(RS-TD sample).In all three samples,macrocracks were formed in the width direction on the outer surface,where tensile stress was predominantly generated in the longitudinal ***,the macrocracks formed in the SS sample were curved because of the merging of uniformly formed fine microcracks,whereas those formed in the RS-TD sample were linear owing to the formation of relatively coarse microcracks along the polishing *** bendability of the samples was in the order of SS>RS-RD>RS-TD,and their limiting bending depths were 4.8,4.6,and 4.4 mm,*** the presence of mechanical-polishing-induced surface roughness,polishing lines perpendicular to the direction of the major stress(i.e.,tensile stress along the longitudinal direction)resulted in a greater degree of stress concentration on the outer surface of the bending *** higher stress concentration promoted the formation of undesirable{10–11}contraction and{10–11}–{10–12}double twins—which typically act as crack initiation sites—and thereby facilitated crack generation and ***,the surface roughness caused premature fracture during bending deformation,which,in turn,caused deterioration of the bendability of the rolled Mg alloy.

关键词： AZ31 alloy Bending Surface roughness Stress concentration Crack

Bending properties of extruded AZ91–0.9Ca–0.6Y alloy and their improvement through precompression and annealing

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Journal of Magnesium and Alloys 2022年第8期10卷 2238-2251页

作者： Jong Un lee gyo myeong lee Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea

In this study,an extruded Mg–9Al–1Zn–0.3Mn–0.9Ca–0.6Y(AZXW9110)alloy is subjected to precompression and subsequent annealing(PCA)treatment for improving its bending formability,and the three-point bending properties of the as-extruded material and the precompressed and subsequently annealed(PCAed)material at room temperature are *** bending,microcracks formed in undissolved Al2Ca,Al2Y,and Al8Mn4Y particles propagate along the grain boundaries or twin boundaries and consequently form a macrocrack in the tension zones of the bending samples of both the ***,the bending formability of the PCAed material is 75%higher than that of the as-extruded material owing to the promoted twinning and slip behaviors in the *** as-extruded material has a strong normal direction(ND)texture and a weak transverse direction(TD)texture,and the ND-and TD-oriented grains are unfavorable for both{10–12}twinning and basal slip in the tension zone of the bending sample of this material,which eventually results in its low bending *** PCAed material has a strong extrusion direction(ED)texture,weak TD texture,and spread ND *** bending,{10–12}twins are fully formed in the ED-oriented grains,and this{10–12}twinning effectively accommodates the plastic strain in the tension *** addition,the activation of basal slip in the ND-oriented grains of the PCAed material is promoted owing to the spread ND texture of this ***,this material exhibits substantially superior bending formability because of the vigorous{10–12}twinning in its ED-oriented grains and promoted basal slip in its ND-oriented grains.

关键词： Magnesium Bending Formability Twinning Texture

Microstructural evolution of pre-twinned Mg alloy with annealing temperature and underlying boundary migration mechanism

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Journal of Magnesium and Alloys 2023年第8期11卷 2953-2966页

作者： Ye Jin Kim Jong Un lee gyo myeong lee Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea

This study investigates the variations in the microstructural characteristics of a pre-twinned Mg alloy with the temperature of the subsequent annealing *** this end,a rolled AZ31 alloy is compressed to 3%plastic strain along the rolling direction(RD)to activate{10-12}twinning and is subsequently annealed at 200,250,300,350,and 400℃.Numerous{10-12}twins are formed throughout the compressed material,leading to the formation of a RD-oriented *** an annealing temperature of 200℃,no microstructural variations occur during *** the annealing temperature increases from 250 to 400℃,the residual strain energy and remaining twin boundaries of the annealed material decrease owing to the promoted static recovery and the increased area fraction of twin-free grown ***,an increase in the annealing temperature results in a gradual microstructural transition from a fully twinned grain structure to a completely twin-free grain *** microstructural evolution during annealing is predominantly governed by the movement of high-angle grain boundaries via a strain-induced boundary migration mechanism,and a few twin boundaries migrate above 350℃because of their lower boundary *** boundary migration behavior and resultant microstructural evolution are discussed in detail based on the variations in boundary mobility and driving force for boundary migration with annealing temperature.

关键词： Rolled Mg alloy {10-12}twin Grain growth Boundary migration Annealing

Effect of characteristics and distribution of Mg_(17)Al_(12)precipitates on tensile and bending properties of high-Al-containing Mg alloys

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Journal of Magnesium and Alloys 2024年第2期12卷 779-793页

作者： Sumi Jo gyo myeong lee Jong Un lee Young Min Kim Sung Hyuk Park School of Materials Science and Engineering Kyungpook National UniversityDaegu 41566Republic of Korea Department of Magnesium Korea Institute of Materials ScienceChangwon 51508Republic of Korea

This study investigates the effect of characteristics and distribution of Mg_(17)Al_(12)precipitates on the uniaxial tensile and three-point bending properties of extruded Mg alloys containing high Al *** extruded Mg–9Al–1Zn–0.3Mn(AZ91)alloy contains lamellar-structured Mg_(17)Al_(12)discontinuous precipitates along the grain boundaries,which are formed via static precipitation during natural air *** extruded Mg–11Al–1Zn–0.3Mn(AZ111)alloy contains spherical Mg_(17)Al_(12)precipitates at the grain boundaries and inside the grains,which are formed via dynamic precipitation during *** to inhomogeneous distribution of precipitates,the AZ111 alloy consists of two different precipitate regions:precipitate-rich region with numerous precipitates and finer grains and precipitate-scarce region with a few precipitates and coarser *** AZ111 alloy exhibits a higher tensile strength than the AZ91 alloy because its smaller grain size and more abundant precipitates result in stronger grain-boundary hardening and precipitation hardening effects,***,the tensile elongation of the AZ111 alloy is lower than that of the AZ91 alloy because the weak cohesion between the dynamic precipitates and the matrix facilitates the crack initiation and *** bending,a macrocrack initiates on the outer surface of bending specimen in both *** AZ111 alloy exhibits higher bending yield strength and lower failure bending strain than the AZ91 *** bending specimens of the AZ91 alloy have similar bending formability,whereas those of the AZ111 alloy exhibit considerable differences in bending formability and crack propagation behavior,depending on the distribution and number density of precipitates in the *** bending specimens of the AZ111 alloy,it is found that the failure bending strain(ε_(f,bending))is inversely proportional to the area fraction of precipitates in the outer zone of bending specimen(A_(ppt)),with a relation

关键词： Mg–Al alloy Extrusion Bending Precipitation Microstructure

Aligned Ion Conduction Pathway of Polyrotaxane‑Based Electrolyte with Dispersed Hydrophobic Chains for Solid‑State Lithium–Oxygen Batteries

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Nano-Micro Letters 2025年第2期17卷 169-186页

作者： Bitgaram Kim myeong‑Chang Sung Gwang‑Hee lee Byoungjoon Hwang Sojung Seo Ji‑Hun Seo Dong‑Wan Kim Department of Materials Science and Engineering Korea University145 Anam‑RoSeongbuk‑GuSeoul 02841Republic of Korea School of Civil Environmental and Architectural EngineeringKorea University145 Anam‑RoSeongbuk‑GuSeoul 02841Republic of Korea Materials Science and Chemical Engineering Center Institute for Advanced Engineering(IAE)Yongin 17180Republic of Korea

A critical challenge hindering the practical application of lithium–oxygen batteries(LOBs)is the inevitable problems associated with liquid electrolytes,such as evaporation and safety *** study addresses these problems by proposing a modified polyrotaxane(mPR)-based solid polymer electrolyte(SPE)design that simultaneously mitigates solvent-related problems and improves ***-SPE exhibits high ion conductivity(2.8×10^(−3)S cm^(−1)at 25℃)through aligned ion conduction pathways and provides electrode protection ability through hydrophobic chain *** this mPR-SPE into solid-state LOBs resulted in stable potentials over 300 *** situ Raman spectroscopy reveals the presence of an LiO_(2)intermediate alongside Li_(2)O_(2)during oxygen *** situ X-ray diffraction confirm the ability of the SPE to hinder the permeation of oxygen and moisture,as demonstrated by the air permeability *** present study suggests that maintaining a low residual solvent while achieving high ionic conductivity is crucial for restricting the sub-reactions of solid-state LOBs.

关键词： Solid polymer electrolyte Lithium-oxygen batteries Polyrotaxane ion conductivity Hydrophobic chain

Pressure Wave and Fluid Velocity in a Bend-Mode Inkjet Nozzle with Double PZT Actuators

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Journal of Thermal Science 2013年第1期22卷 29-35页

作者： Sungu Kim Jaeyong Sung myeong Ho lee Graduate School Dept.of Mechanical EngineeringSeoulTech Dept.of Mechanical and Automotive Engineering SeoulTech

A new concept of bend-mode inkjet nozzle with double PZT (lead zirconate titanate) actuators has been designed and fabricated in the present study. Then the pressure wave and fluid velocity at the nozzle exit have been investigated. The complex pressure behavior inside the channel was solved numerically based on the narrow channel acoustic theory. The two PZTs attached to a rectangular channel were actuated sequentially by setting the waveforms of each PZT to be center-aligned with various pulse widths. As a result, the double PZT actuation is superior to the single PZT actuation in view of strong momentum force and fast dissipation of residual pressure. The maximum fluid velocity at the nozzle exit is observed when the respective pulse widths equal to their optimum pulse widths. The numerical results are supported by the experimental results with the fabricated inkjet device by measuring the speed of meniscus just out of the nozzle.

关键词： double PZT actuators inkjet nozzle narrow channel theory pressure wave sequential actuation

Laser transformation hardening on rod-shaped carbon steel by Gaussian beam

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中国有色金属学会会刊：英文版 2009年第4期19卷 941-945页

作者： Jong-Do KIM myeong-Hoon lee Su-Jin lee Woon-Ju KANG Division of Marine System Engineering College of Maritime SciencesKorea Maritime University Graduate School Korea Maritime University

Laser transformation hardening(LTH) is one of the laser surface modification *** surface hardening of rod-shaped carbon steel(SM45C) was performed by lathe-based laser composite processor with Gaussian-beam optical *** LTH characteristics by dominant processes,longitudinal and depth directional hardness distributions and behaviors of phase transformation in hardened zones were ***,two concepts of circumferential speed and theoretical overlap rate were *** laser power increased or circumferential speed decreased,the surface hardening depth gradually increases due to the increased heat ***,the longitudinal hardness distribution particularly shows periodicity of repetitive increase and decrease,which results from tempering effect by ***,the feasibility of laser transformation hardening is verified by using the beam with Gaussian intensity distribution.

关键词：激光相变硬化高斯光束碳素钢表面强化硬度分布圆周速度改性过程相变行为

Effect of post heat-treatment on the microstructure and high-temperature oxidation behavior of precipitation hardened IN738LC superalloy fabricated by selective laser melting

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Journal of Materials Science & Technology 2021年第17期76卷 95-103页

作者： Kyu-Sik Kim Sangsun Yang myeong-Se Kim Kee-Ahn lee Department of Materials Science and Engineering Inha UniversityIncheon 22212Republic of Korea Korea Institute of Materials Science Changwon51508Republic of Korea Auratech Co. Ltd.Seongnam13449Republic of Korea

The present study investigated the effect of as-built and post heat-treated microstructures of IN738LC alloy fabricated via selective laser melting process on high temperature oxidation *** as-built microstructure showed fine cell and columnar structure due to high cooling *** element segregation was observed in inter-cell/inter-columnar *** post heat-treatment,the initially-observed cell structure disappeared,instead bimodal Ni_3(Al,Ti)particles *** temperature(1273 K and 1373 K)oxidation test results showed parabolic oxidation curves regardless of temperature and initial *** as-built IN738LC fabricated via the selective laser melting process displayed oxidation resistance similar to or slightly better than that of IN738LC fabricated via wrought or cast ***-treated SLM IN738LC,although had similar oxidation weight-gain values to those of the SLM asbuilt material at 1273K,showed relatively better oxidation resistance at 1373 *** Ni_3(Al,Ti)precipitate formed in the post heat treatment changed the local chemical composition,thereby led to changes in alumina former/chromia former location and fraction on the alloy *** was concluded that in heat-treated IN738LC increased alumina former fraction was found,and this resulted in excellent oxidation resistance and relatively low weight-gain.

关键词： IN738LC Selective laser melting High temperature oxidation Post heat-treatment Oxidation mechanism