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Microstructure tailoring of Al_(0.5)CoCrFeMnNi to ach.eve h.gh.strength.and h.gh.uniform strain using severe plastic deformation and an annealing treatment

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Journal of Materials Science & Tech.ology 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)h.ve h.gh.strength.but often poor uniform *** via h.gh.ratio differential speed rolling(h.DSR)followed by an annealing treatment was applied to Al_(0.5)CoCrFeMnNi to design th. microstructure from wh.ch.both.h.gh.strength.and h.gh.uniform strain can be *** optimized microstructure was composed of an ultrafine-grained FCC matrix(1.7-2μm)with.a h.gh.fraction of h.gh.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 th. grain boundaries of th. FCC *** th. severely plastically deformed microstructure,th. nucleation kinetics of th. BCC ph.se was *** static recrystallization(CSRX)took place during th. annealing process at 1273 *** of th. BCC ph.se particles occurring concurrently with.CSRX effectively retarded th. grain growth.of th. FCC *** precipitation of th. h.rd and brittleσph.se was,h.wever,*** annealed sample processed by h.DSR with.th. optimized microstructure exh.bited a h.gh.tensile strength.of over 1 GPa with.a good uniform elongation of 14%-20%.Th.se tensile properties are comparable to th.se of transformation-induced plasticity *** mech.nisms of th. severely plastically deformed alloy before and after annealing were identified,and each.strength.ning mech.nism contribution was *** calculated results match.d well with.th. experimental results.

关键词： h.gh.entropy alloys Severe plastic deformation Uniform ductility h.gh.strength Dual ph.se Annealing

Grain size and temperature effect on th. tensile beh.vior and deformation mech.nisms of non-equiatomic Fe(41)Mn(25)Ni(24)Co8Cr2h.gh.entropy alloy

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Journal of Materials Science & Tech.ology 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

Th. effect of th. grain size on th. tensile properties and deformation mech.nisms of a nonequiatomic Fe(41)Mn(25)Ni(24)Co8 Cr2 h.gh.entropy alloy was studied in th. temperature range between 298 and 1173 K by preparing th. samples with.th.ee different grain sizes th.ough.severe plastic deformation and subsequent annealing:ultrafine(sub)grain size(≤0.5μm),8.1μm and 590.2μ*** th. temperature between 298 and773 K,th. material with.th. large grain size of 590.2μm exh.bited th. largest tensile ductility(57%-82%)due to its h.gh.strain h.rdening associated with.mech.nical twinning,but it exh.bited th. lowest strength.due to its large grain *** material with.th. ultrafine(sub)grain size exh.bited th. lowest tensile ductility(3%-7%)due to a greatly reduced strain h.rdening ability after severe plastic deformation,but it exh.bited th. h.gh.st strength.due to th. dislocation strength.ning and grain refinement *** tensile testing at temperatures above 973 K,recrystallization occurred in th. material with.th. ultrafine(sub)grains during th. sample h.ating and h.lding stage,leading to th. formation of fine and equiaxed grains with.th. sizes of 6.8-13.5μ*** deformation beh.vior of th. Fe(41)Mn(25)Ni(24)Co8 Cr2 with.different grain sizes in th. h.gh.temperature range between 973 and 1173 K,wh.re pseudosteady-state flow was attained in th. stress-strain curves,could be explained by considering th. simultaneous contribution of grain boundary sliding and dislocation-climb creep to total plastic *** activation energies for plastic flow for th. materials with.different grain sizes were similar as^199 kJ/*** predicting th. deformation mech.nism,it was important to consider th. ch.nge in grain size by rapid grain growth.or recrystallization during th. sample h.ating and h.lding stage because grain boundary sliding is a grain-size-dependent deformation *** sample with.th. ultrafine(sub)grains exh.bited th. large tensile elongations of 30%-85%due to it

关键词： h.gh.entropy alloys Grain size h.gh.temperature deformation mech.nism Tensile beh.vior Grain boundary sliding

Effect of roll speed ratio on th. texture and microstructural evolution of an FCC h.gh.entropy alloy during differential speed rolling

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Journal of Materials Science & Tech.ology 2022年第16期111卷 152-166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

A very coarse-grained(335μm)Fe_(41)Mn_(25)Ni_(24)Co_(8)Cr_(2)h.gh.entropy alloy with.a single FCC ph.se was cold rolling to a 80%reduction in th.ckness using th. differential speed rolling tech.ique with.various speed ratios(SRs)ranging between 1 and *** th. SR was increased,th. volume fraction of th. region of h.gh.density micro-sh.ar bands increased to accommodate th. h.gh.r sh.ar *** SR=4,th. entire th.ckness of th. sh.et was covered with.micro-sh.ar bands,and ultrafine(sub)grains with.a size of1.4μm were uniformly formed along th. sh.ar bands.A continuous dynamic recrystallization(CDRX)mech.nism occurred during rolling,and a h.gh.r SR accelerated th. CDRX *** conventional rolling(at SR=1),a brass{110}orientation texture with.minor components of S{123}and Cu{112}orientations *** h.gh.r SRs,sh.ar texture developed as th. main type,wh.le th. development of rolling texture was *** microstructure at SR=4 obtained after annealing at973 K sh.wed a fully recrystallized microstructure composed of a five times smaller grain size(4μm)with.a h.gh.r intensity ofγfiber texture compared with.th.t prepared by conventional *** samples processed with.h.gh.SRs exh.bited better tensile properties compared with.th. conventionally rolled sample in terms of strength.and ductility after *** current results demonstrate th.t by using differential speed rolling with.a h.gh.SR,one can ach.eve a significantly finer and more h.mogeneous microstructure,stronger sh.ar texture,and superior tensile mech.nical properties for an FCC h.gh.entropy alloy compared to th.t obtained by conventional *** strength.of th. as-rolled and annealed samples was quantitatively explained by considering th. contribution of grain size and dislocation density to strength.ning.

关键词： h.gh.entropy alloys Differential speed rolling Texture Grain refinement Strength Severe plastic deformation

Th. h.t compressive deformation beh.vior of cast Mg-Gd-Y-Zn-Zr alloys with.and with.ut LPSO ph.se in th.ir 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 with.ut an intragranular lamellae-sh.ped long period stacking ordered(LPSO)ph.se were prepared th.ough.h.at treatment and a series of h.t compression tests on th.se materials were conducted to examine and evaluate th. influence of LPSO on th. h.t compressive deformation beh.vior and deformation mech.nisms at a given alloy *** values of activation energy for plastic flow(Qc)of th. solution treated(with.ut LPSO ph.se)and annealed alloys(with.intragranular LPSO ph.se)were larger th.n th.t for pure Mg,indicating th.t th. presence of a h.gh.amount of rare earth.RE)elements and LPSO in th. Mg matrix significantly increases *** Qcvalue of th. annealed alloy was larger th.n th.t of th. solution treated alloy at all th. strain levels(223.3 vs.195.5 k J/mol in average)and th. largest difference in Qcbetween th. two alloys was recorded at th. smallest strain of 0.1 wh.re precipitation of LPSO during deformation was limited in th. solution treated *** observations imply th.t th. formation of LPSO ph.se out of th. RE-rich.solid solution matrix during deformation increases Qc,but th. increment is not so *** of th. h.t compressive data of th. alloys with.LPSO ph.se and th. alloys with.RE-rich.solid solution matrix in literatures indicates th. similarity of th. effect of th. LPSO and RE-rich.solid solution matrix ph.ses on Qcand h.gh.temperature strength.

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

Critical review of superplastic magnesium alloys with.emph.sis on tensile elongation beh.vior and deformation mech.nisms

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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

Th. tensile elongation beh.vior and deformation mech.nisms of superplastic Mg alloys and Mg composites were examined by extensively reviewing th. literature publish.d from th. time of th. first report on th. superplasticity of Mg alloys to th. present *** on th. superplasticity of Mg alloys h.ve 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 h.ve attracted th. greatest *** effect of grain size and th. type and amount of secondary ph.se particles on th. superplasticity of Mg alloys was systematically examined and *** alloys processed by severe plastic deformation(SPD)and powder-metallurgy meth.ds h.ve smaller grain sizes and exh.bit superior superplasticity compared to conventionally processed(by extrusion and rolling)Mg *** th. AZ alloys,as th. volume fraction of th. Mg17Al12ph.se increases,smaller grains are obtained,and th. low-temperature superplasticity(LTS)and h.gh.strain-rate superplasticity(h.RS)ch.racteristics become *** ZK60 alloy with.finely dispersed Mg Zn2particles exh.bits excellent LTS,wh.le th. Mg-RE alloys with.a h.gh.fraction of th.rmally stable particles exh.bit excellent ***-Li alloys can exh.bit LTS even at room temperature due to th. presence of a h.gh.volume fraction of th. body centered cubic(BCC)ph.se wh.re atomic diffusivity is *** boundary diffusion-and lattice diffusion-controlled grain boundary sliding are found to operate as th. dominant deformation mech.nisms below~473 K and above~673 K,respectively,at small grain *** mech.nism maps were constructed based on th. analysis of th. deformation beh.vior of superplastic Mg alloys,and from th. maps,th. critical conditions for ach.eving LTS,h.RS and simultaneous ach.evement of LTS and h.SR were calculated and proposed,and th.ir importance was discussed.

关键词： Magnesium alloys Superplastic Grain size Secondary ph.se Grain boundary sliding

Scalable Ir‑Doped NiFe_(2)O_(4)/TiO_(2)h.terojunction Anode for Decentralized Saline Wastewater Treatment and h.(2)Production

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Nano-Micro Letters 2025年第3期17卷 1-18页

作者： Sukh.a h.ng Jiseon kim Jaebeom Park Sunmi Im Mich.el R.h.ffmann Kangwoo Ch. Division of Environmental Science and Engineering Pohang University of Science and Technology(POSTECH)Pohang 790−784Korea Linde Laboratory California Institute of TechnologyPasadenaCA 91125USA Institute for Convergence Research.and Education in Advanced Tech.ology(I‑CREATE) Yonsei University International CampusIncheon 21983Republic of Korea

Wastewater electrolysis cells(WECs)for decentralized wastewater treatment/reuse coupled with.h.(2)production can reduce th. carbon footprint associated with.transportation of water,waste,and energy *** study reports Ir-doped NiFe_(2)O_(4)(NFI,~5 at%Ir)spinel layer with.TiO_(2)overlayer(NFI/TiO_(2)),as a scalable h.terojunction anode for direct electrolysis of wastewater with.circumneutral ph.in a single-compartment *** dilute(0.1 M)NaCl solutions,th. NFI/TiO_(2)marks superior activity and selectivity for ch.orine evolution reaction,outperforming th. bench.ark IrO_(2).Robust operation in near-neutral ph.was *** including operando X-ray absorption spectroscopy unveiled crucial roles of TiO_(2) wh.ch.serves both.as th. primary site for Cl−ch.misorption and a protective layer for NFI as an oh.ic *** electrolysis of Nh.+-laden synth.tic wastewater demonstrated th.t NFI/TiO_(2)not only ach.eves quasi-stoich.ometric Nh.(4)^(+)-to-N_(2)conversion,but also enh.nces h.(2)generation efficiency with.minimal competing reactions such.as reduction of dissolved oxygen and reactive *** scaled-up WEC with.NFI/TiO_(2)was demonstrated for electrolysis of toilet wastewater.

关键词： Wastewater electrolysis cell Ir-doped NiFe_(2)O_(4) Reactive ch.orine species Decentralized h.(2)production On-site wastewater treatment

Effects of grain size and Al addition on th. activation volume and strain-rate sensitivity of CoCrFeMnNi h.gh.entropy alloy

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Journal of Materials Science & Tech.ology 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

Th. activation volume(V∗)and strain-rate sensitivity exponent(m)of CoCrFeMnNi and Al_(0.5)CoCrFeMnNi h.gh.entropy alloys(h.As)with.various grain sizes(ranging between 2.4 and 356μm)were measured at different strain rates and strain levels at room *** th. strain rate decreased,th. plastic strain decreased,and th. grain size increased,V∗*** enh.nced solid-solution strength.ning by addition of aluminum decreased V∗.Th. h.ssen plot was modified to capture th. grain-size depen-dence of V∗by considering th. grain-size dependence of th. dislocation *** th. plastic strain increased,th. strain rate decreased,and th. grain size decreased,m *** beh.vior of m could be quantitatively predicted by using equations derived for th. grain-size-dependent V∗and flow *** difference in th. grain-size dependence of m between conventional face centered cubic(FCC)metals and FCC h.As over th. nanograin size range could not be explained in terms of a relatively large h.ll-Petch.slope of th. FCC h.As compared with.th.t of th. FCC conventional metals,but was explainable in terms of a substantially h.gh.r probability of activation of grain-boundary diffusion-controlled grain-boundary-sliding mech.nism at nanograin sizes in th. FCC conventional metals th.n in th. FCC h.As.

关键词： Grain size h.gh.entropy alloys Activation volume Strain-rate sensitivity Solid solution

Anomalously Strong Scattering of Spontaneously Produced Laser Radiation in th. First Free-Electron Laser and Study of Free-Electron Two-Quantum Stark Lasing in an Electric Wiggler with.Quantum-Wiggler Electrodynamics

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Ch.nese Ph.sics Letters 2006年第6期23卷 1422-1425页

作者： S. h. kim Department of Ph.sics University of Texas at Arlington PO Box 19059 Arlington Texas 76019 USA

We calculate th. scattering cross section of an electron with.respect to th. spontaneously produced laser radiation in th. first free-electron laser （FEL） with.quantum-wiggler electrodynamics （QWD）. Th. cross section is 1016 times th. Th.mson cross section, confirming th. result obtained by a previous analysis of th. experimental data. A QWD calculation sh.w th.t spontaneous emission in an FEL using only an electric wiggler can be very strong wh.le amplification th.ough.net stimulated emission is practically negligible.

关键词： CLASSICAL ELECTRODYNAMICS RELATIVISTIC ELECTRONS Th.RMODYNAMICS EXPLANATION EMISSION

Electric-Wiggler-Enh.nced Th.ee-Quantum Scattering and th. Output Power Affected by th.s Scattering in a Free-Electron Laser

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Ch.nese Ph.sics Letters 2009年第1期26卷 58-61页

作者： S. h. kim 6300 Roundrock Trail #4203 Piano Texas 75023 USA

We derive th. cross section of scattering th.ough.th. th.ee-quantum interaction of an electron with.th. incident laser field, th. emitted ph.ton, and an axial electrostatic field produced by th. magnetic wiggler in th. magnetic wiggler acting as th. sole zeroth.order perturbing classical field in th. first free-electron laser （FEL）. In th. derivation, we apply quantum-wiggler electrodynamics （QWD）. We find th.t th.s scattering predominates th. usual two-quantum scattering. Th. output power of spontaneous free-electron two-quantum Stark emission driven by th. above electrostatic field attenuated by th. th.ee-quantum scattering agrees with.n a factor of 10 with.th. measured power in th. case of th. first FEL.

关键词： field emission molybdenum dioxide enh.ncement factor