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Tailoring high-refractive-index nanocomposites for manufacturing of ultraviolet metasurfaces

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Microsystems & Nanoengineering 2024年第2期10卷 303-310页

作者： Hyunjung Kang Dongkyo Oh Nara Jeon Joohoon Kim Hongyoon Kim Trevon Badloe Junsuk Rho Department of Mechanical Engineering Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea graduate school of Artificial Intelligence Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea Department of Chemical Engineering Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea Department of Electrical Engineering Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea POSCO-postech-RIST Convergence Research Center for Flat Optics and Metaphotonics PohangRepublic of Korea National Institute of Nanomaterials technology(NINT) PohangRepublic of Korea

Nanoimprint lithography(NIL)has been utilized to address the manufacturing challenges of high cost and low throughput for optical *** overcome the limitations inherent in conventional imprint resins characterized by a low refractive index(n),high-n nanocomposites have been introduced to directly serve as ***,comprehensive research on these nanocomposites is notably *** this study,we focus on the composition of high-n zirconium dioxide(ZrO_(2))nanoparticle(NP)concentration and solvents used to produce ultraviolet(UV)metaholograms and quantify the transfer fidelity by the measured conversion *** utilization of 80 wt%ZrO_(2)NPs in MIBK,MEK,and acetone results in conversion efficiencies of 62.3%,51.4%,and 61.5%,respectively,at a wavelength of 325 *** analysis of the solvent composition and NP concentration can further enhance the manufacturing capabilities of high-n nanocomposites in NIL,enabling potential practical use of optical metasurfaces.

关键词： ultraviolet refractive nanocomposites

Activation of non-basal ＜c + a> slip in multicomponent Mg alloys

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Journal of Magnesium and Alloys 2022年第2期10卷 585-597页

作者： Hyo-Sun Jang Jong-Kwan Lee Antonio Jo?o Seco Ferreira Tapia Nack Joon Kim Byeong-Joo Lee Department of Materials Science and Engineering Pohang University of Science and Technology (POSTECH) graduate Institute of ferrous technology Pohang University of Science and Technology (POSTECH)

Activating non-basal slip is a key method to improve room temperature ductility and formability of Mg alloys. However, the detailed criterion for activation of the slip in multicomponent Mg alloys, which can be utilized in commercial Mg alloys, requires further understanding. The present authors investigated the mechanism and criterion using a molecular statics simulation on dislocation behaviors in multicomponent Mg alloys. We found that if multicomponent Mg alloys have an equivalent dislocation binding intensity to associated binary Mg alloys that are optimized to minimize the critical resolved shear stress anisotropy and thus activate the slip,then the critical resolved shear stress anisotropy between slip systems of the multicomponent Mg alloys can also be minimized, resulting in activation of the slip. The activation is maximized in multicomponent Mg alloys when alloying a large amount of weak dislocation binding elements. It was confirmed through experiments that the multicomponent Mg alloys satisfying the above criterion show higher room-temperature tensile elongation and formability than other alloys.

关键词： Mg–Zn–Ca alloy Molecular statics simulation Ductility Formability

Dynamic Response of Mold Oscillator Interacting with Steel Slabs

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Journal of Iron and Steel Research International 2016年第9期23卷 900-909页

作者： Yonghui PARK Hyunchul PARK graduate school of Engineering Masterships Pohang University of Science and Technology(POSTECH)

A mathematical model to show the dynamic response of the mold oscillator was suggested. The model con- sidered a frictional interaction between the mold oscillator and slab as several connected nodes. The governing equation considered the slab as a multi-degree-of-freedom （DoF） system, and included a hysteresis model to describe elastic-plastic behavior of the slab; the mold oscillator was given two DoF by utilizing pressure and displacement experiment data. Simulations indicate that the mold and slab execute various vibrations, and that mold oscillation marks are caused by a stick-and-slip phenomenon during intervals, in which the slab contacting the mold moves downward compared to the other slab （negative strip time）. The slab shows the formation of mold oscillation marks to previous formation criterion equally when the mold velocity is faster than the casting speed about downward. The oscillation mark will grow up over 2 Hz exciting frequency with constant 4 mm stroke in simulations. Finally, the negative strip time was compared to the frictional force, hysteresis variable, and plastic force to investigate formation mechanism of the oscillation marks.

关键词： mold oscillating mechanism mathematical model direct integration method hysteresis model stick-and-slip

Functionally graded structure of a nitride-strengthened Mg_(2)Si-based hybrid composite

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Journal of Magnesium and Alloys 2024年第3期12卷 1239-1256页

作者： Jeongho Yang Woongbeom Heogh Hogi Ju Sukhyun Kang Tae-Sik Jang Hyun-Do Jung Mohammad Jahazi Seung Chul Han Seong Je Park Hyoung Seop Kim Susmita Bose Amit Bandyopadhyay Martin Byung-Guk Jun Young Won Kim Dae-kyeom Kim Rigoberto CAdvincula Clodualdo Aranas Jr Sang Hoon Kim school of Mechanical Engineering Pusan National UniversityBusan 46241Republic of Korea Department of Mechanical Design Engineering Hanyang UniversitySeoul 04763Republic of Korea Process Research 3 Team LG Display Co.Ltd.PajuGyeonggi-do 10845Republic of Korea Department of Materials Science and Engineering Chosun UniversityGwangju 61452Republic of Korea Institute of Well-Aging Medicare&Chosun University LAMP Center Chosun UniversityGwangju 61452Republic of Korea Division of Materials Science and Engineering Hanyang UniversitySeoul 04763Republic of Korea Department of Mechanical Engineering École de Technologie SupérieureMontrealQuebec H3C 1K3Canada Material&Component Convergence R&D Center Korea Construction Equipment Technology InstituteGunsanJeollabuk-do 54002Republic of Korea school of Mechanical and Aerospace Engineering Nanyang Technological UniversitySingapore 639798Singapore graduate Institute of ferrous&Eco Materials technology Pohang University of Science and TechnologyPohangGyeongsangbuk-do 37673Republic of Korea Advanced Institute for Materials Research Tohoku UniversitySendai 980-8577Japan Institute for Convergence Research and Education in Advanced technology Yonsei UniversitySeoul 03722Republic of Korea school of Mechanical and Materials Engineering Washington State UniversityPullmanWashington 99164USA school of Mechanical Engineering Purdue UniversityWest LafayetteIndiana 47907USA Research Institute of Advanced Manufacturing technology Korea Institute of Industrial TechnologyIncheon 21999Republic of Korea Department of Macromolecular Science and Engineering Case Western Reserve UniversityClevelandOhio 44106USA Department of Chemical and Biomolecular Engineering and Joint Institute for Advanced Materials University of TennesseeKnoxvilleTennessee 37996USA Center for Nanophase Materials and Sciences Oak Ridge National LaboratoryOak RidgeTennessee 37830USA Department of Mechanical Engineering University of New BrunswickFrederictonNew Brunswick E3B 5A3Cana

The ex-situ incorporation of the secondary SiC reinforcement,along with the in-situ incorporation of the tertiary and quaternary Mg_(3)N_(2) and Si_(3)N_(4) phases,in the primary matrix of Mg_(2)Si is employed in order to provide ultimate wear resistance based on the laser-irradiation-induced inclusion of N_(2) gas during laser powder bed *** is substantialized based on both the thermal diffusion-and chemical reactionbased metallurgy of the Mg_(2)Si–SiC/nitride hybrid *** study also proposes a functional platform for systematically modulating a functionally graded structure and modeling build-direction-dependent architectonics during additive *** strategy enables the development of a compositional gradient from the center to the edge of each melt pool of the Mg_(2)Si–SiC/nitride hybrid ***,the coefficient of friction of the hybrid composite exhibits a 309.3%decrease to–1.67 compared to–0.54 for the conventional nonreinforced Mg_(2)Si structure,while the tensile strength exhibits a 171.3%increase to 831.5 MPa compared to 485.3 MPa for the conventional *** outstanding mechanical behavior is due to the(1)the complementary and synergistic reinforcement effects of the SiC and nitride compounds,each of which possesses an intrinsically high hardness,and(2)the strong adhesion of these compounds to the Mg_(2)Si matrix despite their small sizes and low concentrations.

关键词： Laser powder bed fusion Mg_(2)Si-SiC/nitride hybrid composite Both the thermal diffusion-and chemical reaction-based metallurgy Functionally graded structure Compositional gradient Wear resistance.

Super-resolving material microstructure image via deep learning for microstructure characterization and mechanical behavior analysis

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npj Computational Materials 2021年第1期7卷 867-877页

作者： Jaimyun Jung Juwon Na Hyung Keun Park Jeong Min Park Gyuwon Kim Seungchul Lee Hyoung Seop Kim Department of Materials AI&Big-Data Korea Institute of Materials Science(KIMS)Changwon-siRepublic of Korea Department of Mechanical Engineering Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea Department of Materials Science and Engineering Pohrepresent the average grainang University of Science and Technology(POSTECH)PohangRepublic of Korea graduate school of Artificial Intelligence Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea graduate Institute of ferrous technology Pohang University of Science and Technology(POSTECH)PohangRepublic of Korea

The digitized format of microstructures,or digital microstructures,plays a crucial role in modern-day materials ***,the acquisition of digital microstructures through experimental means can be unsuccessful in delivering sufficient resolution that is necessary to capture all relevant geometric features of the *** resolution-sensitive microstructural features overlooked due to insufficient resolution may limit one’s ability to conduct a thorough microstructure characterization and material behavior analysis such as mechanical analysis based on numerical ***,a highly efficient super-resolution imaging based on deep learning is developed using a deep super-resolution residual network to super-resolved low-resolution(LR)microstructure data for microstructure characterization and finite element(FE)mechanical *** characterization and FE model based mechanical analysis using the super-resolved microstructure data not only proved to be as accurate as those based on high-resolution(HR)data but also provided insights on local microstructural features such as grain boundary normal and local stress distribution,which can be only partially considered or entirely disregarded in LR data-based analysis.

关键词： microstructure Microstructure analysis

Non-metallic inclusions in electroslag remelting:a review

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Journal of Iron and Steel Research International 2021年第12期28卷 1483-1503页

作者： Cheng-bin Shi Shi-jun Wang Jing Li Jung-wook Cho Institute of Advanced Steel State Key Laboratory of Advanced MetallurgyUniversity of Science and Technology Beijing(USTB)Beijing100083China graduate Institute of ferrous and Energy Materials technology Pohang University of Science and Technology(POSTECH)Pohang790-784Republic of Korea

Non-metallic inclusion in electroslag remelting is a constant topic that has been studied for *** results and conclusions are obtained on some of the subjects from these previous *** differences originate in part from different experimental conditions,including original inclusion chemistries in consumable electrode,slag composition,oxygen level,liquid metal compositions,deoxidation schemes,and melting rates of electroslag *** advances in the operating practices of inclusion control in electroslag remelting production are *** evolution during the electroslag remelting and related processing parameters are also reviewed and *** role of the reoxidation of liquid steel during electroslag remelting on oxide inclusion composition is *** generation of inclusions in remelted ingot is critically *** and remaining issues are noted.

关键词： Non-metallic inclusion Electroslag remelting Inclusion removal Reoxidation

Thermodynamic calculations and experiments on inclusions to be nucleation sites for intragranular ferrite in Si-Mn-Ti deoxidized steel

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Journal of University of Science and technology Beijing 2007年第1期14卷 14-21页

作者： Xiaojun Zhuo Xinhua Wang Wanjun Wang Lee Hae-Geon Metallurgical and Ecological Engineering school University of Science and Technology Beijing Beijing 100083 China graduate Institute of ferrous technology Pohang University of Science and Technology Pohang 790-784 South Korea

Microstructures and inclusions in the Si-Mn-Ti deoxidized steels after cooling in the furnace were investigated. The composition and morphology of the inclusions were analyzed using a field emission scanning electron microscope （FE-SEM） with energy dispersive X-ray spectrometry （EDS）. The kind and composition of the inclusions calculated from the thermodynamic database were in good agreement with the experimental results. There were two main kinds of inclusions formed in the Si-Mn-Ti deoxidized steels. One kind of inclusion was the manganese titanium oxide （Mn-Ti oxide）. Another kind of inclusion was the MnS inclusion with segregation points containing Ti and N. According to the thermodynamic calculation, those segregation points were TiN precipitates. The formation of intragranular ferrite （IGF） microstructures refined the grain size during the austenite-ferrite transformation. The mechanisms of IGF formation were discussed. Mn-Ti oxide inclusions with Mn-depleted zone （MDZ） were effective to be nucleation sites for IGF formation, because the MDZ increased the austenite-ferrite transformation temperature. TiN had the low misfit ratio with IGF, so the TiN precipitated on the MnS surface also promoted the formation of IGF because of decreasing interfacial energies.

关键词： Si-Mn-Ti deoxidized steel intragranular ferrite Mn-depleted zone TtN precipitation thermodynamic calculation

Nature of large (Ti, Nb)(C, N) particles precipitated during the solidification of Ti, Nb HSLA steel

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Journal of University of Science and technology Beijing 2007年第2期14卷 112-117页

作者： Xiaojun Zhuo Xinhua Wang Wanjun Wang Hae-Geon Lee Metallurgical and Ecological Engineering school University of Science and Technology Beijing Beijing 100083 China graduate Institute of ferrous technology Pohang University of Science and Technology Pohang 790-784 South Korea

To investigate the microsegregation phenomena and complex （Ti, Nb）（C, N） precipitation behavior during continuous casting, a unidirectional solidification unit was employed to simulate the solidification process. The samples of Ti, Nb-addition steels after unidirectional solidification were examined using field emission scanning electron microscope （FE-SEM） and electron probe X-ray microanalyzer （EPMA）. In such specimens, dendrite structure and mushy zone can be detected along the solidification direction. It shows that the addition of titanium, niobium to high-strength low-alloyed （HSLA） steel results in undesirable （Ti, Nb）（C, N） precipitation because of microsegregation. The effect of cooling rate on （Ti, Nb）（C, N） precipitation was investigated. The composition of large precipitates was determined using FE-SEM with EDS. Large （Ti, Nb）（C, N） precipitates could be divided into three kinds according to the composition and morphology. With the cooling rate increasing, Ti-rich （Ti, Nb）（C, N） precipitates are transformed to Nb-rich （Ti, Nb）（C, N） precipitates.

关键词： carbonitride microsegregation dendritic region unidirectional solidification cooling rate

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