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Microstructure,Elastic Modulus and Tensile Properties of Ti-Nb-O Alloy System

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Journal of Materials Science & Technology 2008年第1期24卷 33-36页

作者： H.S.kim T.Y.Ra i.D.Yeo H.J.Bang Y.G.Yoo w.Y.kim Advanced Materials R＆D Division Korea Institute of Industrial Technology Incheon 406-800 Korea

in the present study Ti-Nb binary alloy system was chosen because it has excellent biocompatibility as well as reasonable mechanical properties,aiming at understanding oxygen content on microstructural formation, elastic modulus and tensile properties in Ti-Nb alloy *** alloy buttons of 50 mm in diameter were prepared by arc melting on a water-cooled copper hearth under an argon gas atmosphere with a non-consumable tungsten *** button ingots were then heat treated in a vacuum atmosphere at 1273 K for 0.5 h followed by water quenching in a specially designed heat treatment ***,elastic modulus and tensile properties were investigated in order to understand the effect of oxygen content in quenched Ti- Nb alloy *** orthorhombic structuredα″martensite was changed to bcc structuredβ-phase with increasing Nb ***,it was found that oxygen makesβ-phase stable in quenched Ti-Nb alloy *** modulus values were sensitive to phase stability of constituent *** strength increased with increasing oxygen *** will be explained by phase formation and stability behavior.

关键词： Ti-Nb-O alloy Phase stability Elastic modulus Mechanical properties

Effect of roll speed ratio on the texture and microstructural evolution of an FCC high-entropy alloy during differential speed rolling

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Journal of Materials Science & Technology 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)high-entropy alloy with a single FCC phase was cold rolling to a 80%reduction in thickness using the differential speed rolling technique with various speed ratios(SRs)ranging between 1 and *** the SR was increased,the volume fraction of the region of high-density micro-shear bands increased to accommodate the higher shear *** SR=4,the entire thickness of the sheet was covered with micro-shear bands,and ultrafine(sub)grains with a size of1.4μm were uniformly formed along the shear bands.A continuous dynamic recrystallization(CDRX)mechanism occurred during rolling,and a higher SR accelerated the CDRX *** conventional rolling(at SR=1),a brassiorientation texture with minor components of S{123}and Cuiorientations *** higher SRs,shear texture developed as the main type,while the development of rolling texture was *** microstructure at SR=4 obtained after annealing at973 K showed a fully recrystallized microstructure composed of a five times smaller grain size(4μm)with a higher intensity ofγfiber texture compared with that prepared by conventional *** samples processed with high SRs exhibited better tensile properties compared with the conventionally rolled sample in terms of strength and ductility after *** current results demonstrate that by using differential speed rolling with a high SR,one can achieve a significantly finer and more homogeneous microstructure,stronger shear texture,and superior tensile mechanical properties for an FCC high-entropy alloy compared to that obtained by conventional *** strength of the as-rolled and annealed samples was quantitatively explained by considering the contribution of grain size and dislocation density to strengthening.

关键词： High entropy alloys Differential speed rolling Texture Grain refinement Strength Severe plastic deformation

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

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

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

Priming of antiherbivore defensive responses in plants

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insect Science 2013年第3期20卷 273-285页

作者： Jinwon kim Gary w. Felton Department of Entomology Pennsylvania State University University Park PA 16802 United States

Abstract Defense priming is defined as increased readiness of defense induction. A growing body of literature indicates that plants （or intact parts of a plant） are primed in anticipation of impending environmental stresses, both biotic and abiotic, and upon the following stimulus, induce defenses more quickly and strongly. For instance, some plants previously exposed to herbivore-inducible plant volatiles （HiPVs） from neighboring plants under herbivore attack show faster or stronger defense activation and enhanced insect resistance when challenged with secondary insect feeding. Research on priming of antiherbivore defense has been limited to the HiPV-mediated mechanism until recently, but significant advances were made in the past three years, including non-HiPV-mediated defense priming, epigenetic modifications as the molecular mechanism of priming, and others. it is timely to consider the advances in research on defense priming in the plant- insect interactions.

关键词： defense priming epigenetic modifications plant-insect interactions

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

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

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