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| 1 | 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显示文摘An ultrafine-grained(UFG) Mg-13Zn-1.55 Y alloy(ZW132) with a high volume fraction(7.4%) of icosahedral phase(I-phase, Mg_3Zn_6Y) 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^(-3)s^(-1) and 523 K-10^(-3)s^(-1),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. | T.Y.Kwak W.J.Kim | 2017 | Journal of Materials Science & Technology2017，33，9： | 9 |
| 2 | Grain size and temperature effect on the tensile behavior and deformation mechanisms of non-equiatomic Fe(41)Mn(25)Ni(24)Co8Cr2high entropy alloy显示文摘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 590.2μm.In 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 size.The 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 strengthening.At 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 6.8-13.5μm.The 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 flow.The activation energies for plastic flow for the materials with different grain sizes were similar as^199 kJ/mol.In 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 mechanism.The sample with the ultrafine(sub)grains exhibited the large tensile elongations of 30%-85%due to its high strain rate sensitivity,m(0.1-0.5)at temperatures of973-1173 K.The material with the large grain size of 590.2μm exhibited the very small elongations of0.2%-8%due to its small m values(0.1-0.2)and occurrence of brittle intergranular fracture at the early stage of plastic deformation. | H.T.Jeong W.J.Kim | 2020 | Journal of Materials Science & Technology2020，42，7： | 5 |
| 3 | 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显示文摘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 magnesium.Compared 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. | T.Y.Kwak W.J.Kim | 2019 | Journal of Materials Science & Technology2019，35，1： | 4 |
| 4 | Microstructure and tensile properties of magnesium nanocomposites fabricated using magnesium chips and carbon black显示文摘In this study,carbon black(0,0.01,0.03 and 0.08 wt%)and AZ31(Mg-3Al-lZn)magnesium chips were used to fabricate carbon black-reinforced magnesium matrix composites with extrusion or a combination of extrusion and high-ratio differential speed rolling.After hot pressing at 693 K and extrusion at 623 K with an extrusion ratio of 22,the magnesium chips coated with carbon black were soundly bonded into a bulk composite material.The grain sizes of the extruded materials were similar with a size of 48.2-51.5|im despite the difference in the amount of carbon black.The yield strength and ultimate tensile strength increased from 177 to 191 MPa and from 240 to 265 MPa,respectively,as a result of the addition of 0.01%carbon black;however,a further increase in the strength was marginal with additional carbon black.The same trend was observed in the strain hardening behavior.The tensile elongation increased by to the addition of 0.01%carbon black(from 15.8%to 17.4%)due to the increased work hardening effect,but decreased with additional carbon black due to its agglomeration and poor dispersion at higher concentration.After high-ratio differential speed rolling(HRDSR)on the extruded materials and subsequent annealing,the AZ31 and AZ31 composites had a similar fine grain size of 16.3-17.9 p.m.The annealed HRDSR composites showed the best mechanical properties at a higher content of carbon black(0.03%)compared to that(0.01%)for the extruded composites.This resulted from the enhanced dispersion effect of the carbon black due to the high shear flow induced during the HRDSR process.The extruded composites exhibited the three distinct hardening stages(stage II,stage III and stage IV),while the annealed HRDSR composites mainly displayed the stage III hardening.The addition of carbon black increased the strain hardening rate at all the strain hardening stages in both of the extruded and annealed HRDSR materials.At the initial hardening stage,the strain hardening rates of the extruded composites were higher than those of the annealed HRDSR composites,but this became reversed at the later stage of hardening.Possible explanations for this observation were discussed.The strength analysis suggests that dislocation-carbon black interaction by Orowan strengthening and dislocation generation due to a difference in thermal expansion between matrix and carbon black are the major strengthening mechanisms. | T.J.Lee W.J.Kim | 2020 | Journal of Magnesium and Alloys2020，8，3： | 3 |
| 5 | Stress corrosion cracking of high-strength AZ31 processed by high-ratio differential speed rolling显示文摘Stress corrosion cracking(SCC)in distilled water was studied for AZ31,processed by differential-speed-rolling to different strengths,using Linear Increasing Stress Tests(LISTs).The stress corrosion crack velocity was 5.0±2.5×10^(−9) m s^(−1),independent of applied stress rate and independent of material strength.SCC susceptibility was greater at lower applied stress rates manifest most importantly as a lower threshold stress for stress corrosion crack initiation.SCC susceptibility could be characterised by the ratio of threshold stress to yield stress,which was dependent on processing details and was as low as 0.3. | Zhiming Shi W.J.Kim Fuyong Cao Matthew S.Dargusch Andrej Atrens | 2015 | Journal of Magnesium and Alloys2015，3，4： | 2 |
| 6 | Effect of roll speed ratio on the texture and microstructural evolution of an FCC high-entropy alloy during differential speed rolling显示文摘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 4.As the SR was increased,the volume fraction of the region of high-density micro-shear bands increased to accommodate the higher shear strain.At 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 process.During conventional rolling(at SR=1),a brass{110}<112>orientation texture with minor components of S{123}<634>and Cu{112}<111>orientations developed.At higher SRs,shear texture developed as the main type,while the development of rolling texture was suppressed.The 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 rolling.The samples processed with high SRs exhibited better tensile properties compared with the conventionally rolled sample in terms of strength and ductility after annealing.The 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 rolling.The strength of the as-rolled and annealed samples was quantitatively explained by considering the contribution of grain size and dislocation density to strengthening. | H.T.Jeong W.J.Kim | 2022 | Journal of Materials Science & Technology2022，，16： | 2 |
| 7 | 查看详情显示文摘 | W.J.Kim W.Chang S.B.Qadri H.D.Wu J.M.Pond S.W.Kirchoefer H.S.Newman D.B.Chrisey and J.S.Horwitz | | 0，，： | 1 |
| 8 | 查看详情显示文摘 | W.J.Kim S.M.Yang | | 0，，： | 1 |
| 9 | The hot compressive deformation behavior of cast Mg-Gd-Y-Zn-Zr alloys with and without LPSO phase in their initial microstructures显示文摘Samples of Mg-8.2Gd-3.8Y-1.1Zn-0.4Zr alloy with and without an intragranular lamellae-shaped long period stacking ordered(LPSO)phase were prepared through heat treatment and a series of hot compression tests on these materials were conducted to examine and evaluate the influence of LPSO on the hot compressive deformation behavior and deformation mechanisms at a given alloy composition.The values of activation energy for plastic flow(Qc)of the solution treated(without LPSO phase)and annealed alloys(with intragranular LPSO phase)were larger than that for pure Mg,indicating that the presence of a high amount of rare earth(RE)elements and LPSO in the Mg matrix significantly increases Qc.The Qcvalue of the annealed alloy was larger than that of the solution treated alloy at all the strain levels(223.3 vs.195.5 k J/mol in average)and the largest difference in Qcbetween the two alloys was recorded at the smallest strain of 0.1 where precipitation of LPSO during deformation was limited in the solution treated alloy.These observations imply that the formation of LPSO phase out of the RE-rich solid solution matrix during deformation increases Qc,but the increment is not so large.Analysis of the hot compressive data of the alloys with LPSO phase and the alloys with RE-rich solid solution matrix in literatures indicates the similarity of the effect of the LPSO and RE-rich solid solution matrix phases on Qcand high-temperature strength. | H.T.Jeong W.J.Kim | 2022 | Journal of Magnesium and Alloys2022，10，10： | 1 |
| 10 | Critical review of superplastic magnesium alloys with emphasis on tensile elongation behavior and deformation mechanisms显示文摘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 day.Studies 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 attention.The effect of grain size and the type and amount of secondary phase particles on the superplasticity of Mg alloys was systematically examined and reviewed.The 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 alloys.For 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 enhanced.The 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 HSRS.Mg-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 high.Grain 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 sizes.Deformation 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. | H.T.Jeong W.J.Kim | 2022 | Journal of Magnesium and Alloys2022，10，5： | 1 |
| 11 | Microstructure tailoring of Al_(0.5)CoCrFeMnNi to achieve high strength and high uniform strain using severe plastic deformation and an annealing treatment显示文摘Ultrafine-grained alloys fabricated by severe plastic deformation(SPD)have high strength but often poor uniform ductility.SPD 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 achieved.The 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 matrix.In the severely plastically deformed microstructure,the nucleation kinetics of the BCC phase was accelerated.Continuous static recrystallization(CSRX)took place during the annealing process at 1273 K.Precipitation of the BCC phase particles occurring concurrently with CSRX effectively retarded the grain growth of the FCC grains.The precipitation of the hard and brittleσphase was,however,suppressed.The 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 steel.Strengthening mechanisms of the severely plastically deformed alloy before and after annealing were identified,and each strengthening mechanism contribution was estimated.The calculated results matched well with the experimental results. | H.T.Jeong W.J.Kim | 2021 | Journal of Materials Science & Technology2021，，12： | 1 |
| 12 | Effects of grain size and Al addition on the activation volume and strain-rate sensitivity of CoCrFeMnNi high-entropy alloy显示文摘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 temperature.As the strain rate decreased,the plastic strain decreased,and the grain size increased,V∗increased.The 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 density.As the plastic strain increased,the strain rate decreased,and the grain size decreased,m decreased.The behavior of m could be quantitatively predicted by using equations derived for the grain-size-dependent V∗and flow stress.The 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. | H.T.Jeong W.J.Kim | 2023 | Journal of Materials Science & Technology2023，，12： | 0 |
| 13 | 胶原蛋白-聚乙烯醇复合再生蛋白纤维的研究显示文摘以从含铬革屑中提取的胶原蛋白为原料,配制分子量不小于100,000Da,且铬含量低于百万分之5的胶原蛋白纺丝原液,采用湿法纺丝制得再生蛋白纤维。为增强纤维的稳定性和力学性能,在胶原蛋白原液中加入戊二醛含量不高于0.3%的聚乙烯醇溶液。通过湿法纺丝实验,发现当原液的粘度高于1000cps时,可获得优良的可纺性。选择以含量不低于40%的硫酸钠和1M的硼酸组成的混合液为凝固浴,温度30℃~35℃的条件下,纺丝原液的成纤性最好。最后,以15%的硫酸钠、0.5%的戊二醛以及0.25%的甲醛溶液为交联剂处理再生纤维以增强抗水性。再生蛋白纤维的线密度为1.3g/cm^2,抗张强度为(1.32~2.0)g/d,伸长率为29%~38%。 | E.C.Shin S.C.Lee W.J.Kim 贾淑平(编译) | 2008 | 北京皮革(中外皮革信息版)(中)2008，，7： | 0 |
| 14 | Superplasticity of fine-grained Mg-10Li alloy prepared by severe plastic deformation and understanding its deformation mechanisms显示文摘The superplastic behavior and associated deformation mechanisms of a fine-grained Mg-10.1 Li-0.8Al-0.6Zn alloy(LAZ1011)with a grain size of 3.2μm,primarily composed of the BCCβphase and a small amount of the HCPαphase,were examined in a temperature range of 473 K to 623 K.The microstructural refinement of this alloy was achieved by employing high-ratio differential speed rolling.The best superplasticity was achieved at 523 K and at strain rates of 10^(-4)-5×10^(-4)s^(-1),where tensile elongations of 550±600%were obtained.During the heating and holding stage of the tensile samples prior to tensile loading,a significant increase in grain size was observed at temperatures above 573 K.Therefore,it was important to consider this effect when analyzing and understanding the superplastic deformation behavior and mechanisms.In the investigated strain rate range,the superplastic flow at low strain rates was governed by lattice diffusion-controlled grain boundary sliding,while at high strain rates,lattice diffusion-controlled dislocation climb creep was the rate-controlling deformation mechanism.It was concluded that solute drag creep is unlikely to occur.During the late stages of deformation at 523 K,it was observed that grain boundary sliding led to the agglomeration of theαphase,resulting in significant strain hardening.Deformation mechanism maps were constructed forβ-Mg-Li alloys in the form of 2D and 3D formats as a function of strain rate,stress,temperature,and grain size,using the constitutive equations for various deformation mechanisms derived based on the data of the current tests. | H.T.Jeong S.W.Lee W.J.Kim | 2024 | Journal of Magnesium and Alloys2024，12，1： | 0 |
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