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Microstructure, precipitates and mechanical properties of powder bed fused inconel 718 before and after heat treatment

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Journal of Materials Science & Technology 2019年第6期35卷 1153-1164页

作者： Le Zhou Abhishek Mehta Brandon McWilliams kyu cho Yongho Sohn Advanced Materials Processing and Analysis Center University of Central Florida Orlando FL 32816 USA Department of Materials Science and Engineering University of Central Florida Orlando FL 32816 USA Weapons and Materials Research Directorate US. Amy Research Laboratory Aberdeen Proving Ground MD 21005 USA

IN718 alloy was fabricated by laser powder bed fusion(PBF) for examination of microstructure, precipitates and mechanical properties in the as-built state and after different heat treatments. The as-built alloy had a characteristic fine cellular-dendritic microstructure with Nb, Mo and Ti segregated along the interdendritic region and cellular boundary. The as-built alloys were then subjected to solution heat treatment(SHT) at 980°C or 1065°C for 1 h. SHT at 980°C led to the formation of δ-phase in the interdendritic region or cellular boundary. The segregation was completely removed by the SHT at 1065°C, but recrystallization was observed, and the carbides decorated along the grain boundaries. The as-built alloy and alloys with SHT at 980°C and 1065°C were two-step aged, which consisted of annealing at 720°C for8 h followed by annealing at 620°C for 8 h. Transmission electron microscopy revealed the precipitation of λ’ and λ" in all alloys after two-step aging, but the amount and uniformity of distribution varied. The Vickers hardness of the PBF IN718 alloy increased from 296 HV to 467 HV after direct aging. The hardness decreased to 267 HV and 235 HV after SHT at 980°C and 1065°C, respectively, but increased to 458 HV and 477 HV followed by aging. The evolution of Young’s modulus after heat treatment exhibited similar trend to that of hardness. The highest hardness was observed for IN718 after SHT at 1065°C and two-step aging due to precipitation with greater amount and uniform distribution.

关键词： Laser powder bed fusion IN718 Microstructure Transmission electron microscopy

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Kinematic Analysis and Experimental Verification on the Locomotion of Gecko

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Journal of Bionic Engineering 2009年第3期6卷 246-254页

作者： Woochul Nam TaeWon Seo Byungwook Kim DongsuJeon kyu-Jin cho Jongwon Kim School of Mechanical and Aerospace Engineering Seoul National University Mechanical Engineering Carnegie Mellon University

This paper presents a kinematic analysis of the locomotion of a gecko,and experimental verification of the kinematic *** analysis is important for parameter design,dynamic analysis,and optimization in biomimetic robot research. The proposed kinematic analysis can simulate,without iteration,the locomotion of gecko satisfying the constraint conditions that maintain the position of the contacted feet on the *** the method has an advantage for analyzing the climbing motion of the quadruped mechanism in a real time *** kinematic model of a gecko consists of four legs based on 7-degrees of freedom spherical-revolute-spherical joints and two revolute joints in the *** motion of the kinematic model is simulated based on measurement data of each *** motion of the kinematic model simulates the investigated real gecko's motion by using the experimental *** analysis solves the forward kinematics by considering the model as a combination of closed and open serial mechanisms under the condition that maintains the contact positions of the attached feet on the ground. The motions of each joint are validated by comparing with the experimental *** addition to the measured gait,three other gaits are simulated based on the kinematic *** maximum strides of each gait are calculated by workspace *** result can be used in biomimetic robot design and motion planning.

关键词： kinematic analysis locomotlon of gecko lizard gait simulation various gaits workspace analysis

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FactSage Thermodynamic Database for Steelmaking Refractory Research

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China's Refractories 2015年第1期24卷 15-21页

作者： In-Ho JUNG Marie-Aline VAN ENDE Mun-kyu cho Zhanmin CAO Mining and Materials Engineering McGill University Research Institute of Industrial Science and Technology School of Metallurgical and Ecological Engineering University of Science and Technology Beijing

Thermodynamic databases are very useful to analyze the complex chemical reactions happening in high temperature material processes. An accurate thermodynamic database based on physically sound thermodynamic models can provide thermodynamic calculations of useful phase diagrams and comprehensive chemical reactions related to refractory corrosion in steelmaking processes. In this study,the FactS age thermodynamic database,one of the most comprehensive thermodynamic databases for oxide systems among other commercial software,is reviewed in particular for the steelmaking refractory research,and several applications to refractory corrosion are presented.

关键词： thermodynamic database CALPHAD FactSage phase diagram corrosion steelmaking

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Reconstruction of cervical necrotizing fasciitis defect with the modified keystone flap technique:Two case reports

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World Journal of Clinical Cases 2024年第7期12卷 1305-1312页

作者： Wonseok cho Eun A Jang kyu Nam Kim Department of Plastic and Reconstructive Surgery Kangbuk Samsung HospitalSungkyunkwan University School of MedicineSeoul 03181South Korea

BACKGROUND Cervical necrotizing fasciitis(CNF)is a rare,aggressive form of deep neck space infection with significant morbidity and mortality *** surgical debridement acts as the cornerstone of CNF treatment;however,it often results in defects requiring complex *** SUMMARY We report two cases in which the keystone flap(KF)was used for CNF defect coverage:Case 1,an 85-year-old patient with CNF in the anterior neck,and Case 2,a 54-year-old patient with CNF in the posterior *** patients received empirical intravenous antibiotic therapy and underwent serial debridement,enabling adequate wound preparation and *** final defect size measured 5.5 cm×12 cm in Case 1 and 6 cm×11 cm in Case *** defect coverage,we employed an 8 cm×19 cm type II KF based on perforators from the superior thyroid artery in Case 1 and a 9 cm×18 cm type II KF based on perforators from the transverse cervical artery in Case *** flaps showed complete *** postoperative complications occurred in both cases,and favorable outcomes were observed at 7-and 6-month follow-ups in case 1 and 2,*** We effectively treated CNF-associated defects using the KF technique;KF is viable for covering CNF defects in carefully selected cases.

关键词： Fasciitis Necrotizing Debridement Plastic surgery Dermatologic surgical procedures Case report

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An Anionic Covalent Organic Framework as an Electrostatic Molecular Rectifier for Stabilizing Mg Metal Electrodes

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CCS Chemistry 2023年第11期5卷 2567-2575页

作者： Zhongping Li Hyunseok Moon Seok-kyu cho Changqing Li Jeong-Min Seo Jong-Beom Baek Hong Xu Sang-Young Lee Department of Chemical and Biomolecular Engineering Yonsei UniversitySeoul 03772 School of Energy and Chemical Engineering Ulsan National Institute of Science and TechnologyUlsan 44919 UBATT Inc. Daejeon 34036 Institute of Nuclear and New Energy Technology Tsinghua UniversityBeijing 100084

Despite its potential as a high-capacity battery electrode,magnesium(Mg)metals are highly susceptible to electrolytes,resulting in the formation of unwanted passivation layers,which hinder charge transfer ***,we first report an anionic covalent organic framework(a-COF)as an electrostatic molecular rectifier(that can preferentially trap solvent molecules)to stabilize Mg metal *** to a neutral COF(n-COF)as a control sample,the a-COF enhances Mg^(2+)transport by facilitating the desolvation of Mg^(2+)-solvent complexes and cationic mobility through its negatively charged one-dimensional columns,thereby achieving an ionic conductivity eight times higher than that of the *** addition,the anionic porous frameworks in contact with Mg metal electrodes enable a uniform Mg^(2+)flux and interfacial stability with Mg metal ***,the a-COF exhibited reversible Mg plating/stripping cyclability on Mg metal electrodes compared to the n-COF,demonstrating the electrochemical viability of the anionic frameworks for Mg metal electrode stabilization.

关键词： anionic covalent organic framework Mg metal electrodes ion transport interfacial stability Mg plating/stripping

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Defect Engineering in Earth-Abundant Cu_(2)ZnSnSe_(4) Absorber Using Efficient Alkali Doping for Flexible and Tandem Solar Cell Applications

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Energy & Environmental Materials 2024年第2期7卷 249-256页

作者： Muhammad Rehan Ara cho Inyoung Jeong Kihwan Kim Asmat Ullah Jun-Sik cho Joo Hyung Park Yunae Jo Sung Jun Hong Seung kyu Ahn SeJin Ahn Jae Ho Yun Jihye Gwak Donghyeop Shin Photovoltaics Research Department Korea Institute of Energy Research(KIER)152-Gajeong-roYuseong-guDaejeon 34129Korea Department of Renewable Energy Engineering University of Science and Technology(UST)217-Gajeong-roYuseong-guDaejeon 34113Korea Korea Institute of Energy Technology(KENTECH) 50772 Ujeong-roNaju Jeonnam 58217Korea

To demonstrate flexible and tandem device applications,a low-temperature Cu_(2)ZnSnSe_(4)(CZTSe)deposition process,combined with efficient alkali doping,was ***,high-quality CZTSe films were grown at 480℃by a single co-evaporation,which is applicable to polyimide(PI)*** of the alkali-free substrate,Na and K alkali doping were systematically studied and optimized to precisely control the alkali distribution in *** bulk defect density was significantly reduced by suppression of deep acceptor states after the(NaF+KF)*** the low-temperature deposition with(NaF+KF)PDTs,the CZTSe device on glass yields the best efficiency of 8.1%with an improved Voc deficit of 646 *** developed deposition technologies have been applied to *** the first time,we report the highest efficiency of 6.92%for flexible CZTSe solar cells on ***,CZTSe devices were utilized as bottom cells to fabricate four-terminal CZTSe/perovskite tandem cells because of a low bandgap of CZTSe(~1.0 eV)so that the tandem cell yielded an efficiency of 20%.The obtained results show that CZTSe solar cells prepared by a low-temperature process with in-situ alkali doping can be utilized for flexible thin-film solar cells as well as tandem device applications.

关键词： alkali doping Earth-abundant Cu_(2)ZnSnSe_(4) flexible solar cells four-terminal tandem cells low-temperature process

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Performance and Effectiveness of UniFET^TM II MOSFET in HID Lamp Ballast

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Journal of Energy and Power Engineering 2012年第12期6卷 2001-2009页

作者： Jae-Eul Yeon Won-Hwa Lee kyu-Min cho Hee-Jun Kim Consumer Power System Team High Voltage Power Conversion Industrial & Automotive Bucheon 420-711 Korea Department of Information and Communication Engineering Yuhan Univisity Bucheon 422-749 Korea School of Electrical and Computer Engineering Hanyang University Ansan 426-791 Korea

An advanced cell structure and lifetime control technology has enhanced on-resistance and reverse recovery performance of power MOSFET （metal oxide semiconductor field-effect transistor） simultaneously. This paper introduces a newly developed planar MOSFET--UniFETTM Ⅱ MOSFET--with highly improved body diode characteristics, and presents its performance and effectiveness. UniFET II MOSFET is divided into normal FET（field effect transistor）, FRFET （fast recovery field effect transistor）, and Ultra FRFET MOSFETs according to the concentration of lifetime control, and their reverse recovery times are about 70%, 25%, and 15% of that of a conventional MOSFET, respectively. To verify the performance and effectiveness of the new MOSFET, an experiment using a 150 W HID （high intensity discharge） lamp ballast that includes a mixed frequency inverter was implemented. As a result, it was verified that two UniFET Ⅱ MOSFETs can replace two conventional MOSFEs and four additional FRDs （fast recovery diodes） without MOSFET failure.

关键词： UniFET Ⅱ FRFET Ultra FRFET MOSFET failure mixed frequency inverter HID ballast.

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Evaluation of the Surface of Nitinol after MR Polishing Process

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Journal of Applied Mathematics and Physics 2015年第2期3卷 208-217页

作者： Byung-Chan Kim Jung-Won Lee Seok-Jae Ha Yong-kyu cho Dong-Sung Kang Myeong-Woo cho Department of Mechanical Engineering Inha University Incheon Republic of Korea WISYS Gunpo-si Republic of Korea

Nitinol is used in various industries, especially for biomaterials. Generally, the surface integrity of sub-micron level and non-surface flaw is required in nitinol for biomaterial. However, surface flaws, such as scratches, pits, and residual stress, can occur on the polished surface, and it is difficult to remove these surface flaws. The corrosion is accelerated continuously and causes bad influence in the body. Therefore, in this study, conventional polishing and MR polishing were used to minimize the corrosion and residual stress when the nitinol is used as biomaterial. X-ray diffraction and Tafel extrapolation were used to investigate the residual stress and the corrosion, and the strain hardening was investigated by nanoindentation. Surface integrities were also evaluated by SEM image and surface roughness results. As a result, the increased residual stress in conventional polishing was decreased by MR polishing. The result of corrosion test was improved from ?301 mV to ?280 mV. The residual stress was improved from ?38.18 MPa to ?31.17 MPa. Finally, it is certified that MR polishing can be used to minimize surface flaws and to improve the corrosion properties.

关键词： Nitinol MR Polishing Corrosion Test Residual Stress Strain Hardening

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Growth-inhibitory effect of neurotrophin-3-secreting adipose tissue-derived mesenchymal stem cells on the D283-MED human medulloblastoma cell line

Growth-inhibitory effect of neurotrophin-3-secreting adipose...

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中国抗癌协会神经肿瘤专业委员会第八届学术会议

作者： Chae-Yong Kim Young-Hoon Kim Seung Hee cho Soo Jung Lee Seung Ah choi Ji Hoon Phi Seung-Ki Kim kyu-Chang Wang Byung-kyu cho Department of Neurosurgery Seoul National University College of Medicine Department of Neurosurgery Seoul National University Bundang Hospital Division of Pediatric Neurosurgery Seoul National University Children's Hospital

Medulloblastoma（MBL）,the most common malignant pediatric brain tumor,is incurable in about one-third of patients and can lead to long-term disabilities despite current multimodal *** purpose of this study was to demonstrate in vitro biological effects of neurotrophins-3（NT-3） on MBL cells and to evaluate the growth-inhibitory effect of neurotrophin-3（NT-3）-secreting stem cells on tumor *** confirmed by western blotting that D283-MED cells express tyrosine kinase C,a specific receptor for *** the biological effects of NT-3 on MBL cells,we evaluated autophagy,apoptosis,senescence,and differentiation of tumor cells with *** NT-3 induced a concentrationdependent increase in apoptosis in the tumor cell line（P ＜ 0.001）.The high concentrations of NT-3 increased the expression of class III β-tubulin（P ＜ 0.001） and decreased the expression of Nestin（P ＜ 0.05）.NT-3-secreting stem cells were produced by nucleofecting ***-NT3 into human adipose tissue-derived mesenchymal stem cells（hAT-MSCs） and were confirmed by fluorescence microscopy and ***-layered co-culture experiments with the NT-3-secreting hAT-MSCs and D283-MED MBL cells were performed,and NT-3-induced cell death was studied by 3-（4,5-dimethylathiazol-2-yl）-2,5-dephenyltetrazolium bromide（MTT） ***,the high concentrations of NT-3-secreting hAT-MSCs significantly（P ＜ 0.05） increased the death of D283-MED cells in *** present study demonstrated that both apoptotic cell death and neuronal differentiation of tumor cells were the mechanisms of growth-inhibitory effect of NT-3-secreting hAT-MSCs on MBL cell line.

关键词： neurotrophin-3 adipose tissue-derived mesenchymal stem cell medulloblastoma apoptosis differentiation

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高氧钢中液态夹杂物对水口耐火材料的侵蚀

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现代冶金（内蒙古） 2016年第1期 65-72页

作者： Mun - kyu cho[韩国]

为了了解在高氧钢中，液态MnO-SiO2-FeO-MnS夹杂物对塞棒耐火材料的侵蚀机理，在1550℃时，完成了液态MnO-SiO2-FeO-MnS渣和几种耐火材料两者之间的化学反应，耐火材料包括Al2O3-C、尖晶石-C、Al2O3-A1N-C和ZrO2-C。结果发现，液态夹杂... 详细信息

为了了解在高氧钢中，液态MnO-SiO2-FeO-MnS夹杂物对塞棒耐火材料的侵蚀机理，在1550℃时，完成了液态MnO-SiO2-FeO-MnS渣和几种耐火材料两者之间的化学反应，耐火材料包括Al2O3-C、尖晶石-C、Al2O3-A1N-C和ZrO2-C。结果发现，液态夹杂物可通过耐火材料中的碳发生还原生成Mn-Fe-Si金属相，还原度是影响液态夹杂物化学组成和数量。根据此试验和热力学研究以及现场试验，发现ZrO2-C（13％）耐火材料对含液态MnO-SiO2-FeO-MnS夹杂物的高氧钢具有极好的耐侵蚀性。

关键词：耐火材料的侵蚀塞棒头液态夹杂物连铸高氧钢

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