Journal of Powder Materials

Young-Keun Jeong

10 Articles

Machinability Evaluation of Hybrid Ti₂ Ceramic Composites with Conductivity in Micro Electrical Discharge Drilling Operation: Jae-Young Heo, Young-Keun Jeong, Myung-Chang Kang, Ahmed Busnaina; J Powder Mater. 2013;20(4):285-290.; DOI: https://doi.org/10.4150/KPMI.2013.20.4.285

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Ti_2AlN composites are a laminated compounds that posses unique combination of typical ceramic properties and typical metallic(Ti alloy) properties. In this paper, the powder synthesis, SPS sintering, composite characteristics and machinability evaluation were systematically conducted. The random orientation characteristics and good crystallization of the Ti_2AlN phase are observed. The electrical and thermal conductivity of Ti_2AlN is higher than that of Ti6242 alloy. A machining test was carried out to compare the effect of material properties on micro electrical discharge drilling for Ti_2AlN composite and Ti6242 alloy. Also, mixture table as a kind of tables of orthogonal arrays was used to know how parameter is main effective at experimental design. Consequently, hybrid Ti_2AlN ceramic composites showed good machining time and electrode wear shape under micro ED-drilling process. This conclusion proves the feasibility in the industrial applications.

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Comparative Study on Ablation Characteristics of Ti-6Al-4V Alloy and Ti₂AlN Bulks Irradiated by Femto-second Laser
Ki Ha Hwang, Hua Feng Wu, Won Suk Choi, Sung Hak Cho, Myungchang Kang
Journal of the Korean Society of Manufacturing Process Engineers.2019; 18(7): 90. CrossRef
Analysis Of Drilling Of A Metal Plate With Pilot Hole
K.S. Kim
Archives of Metallurgy and Materials.2015; 60(2): 1307. CrossRef

Optimization of PEALD-Ru Process using Ru(EtCp)₂: Se-Hun Kwon, Young-Keun Jeong; J Powder Mater. 2013;20(1):19-23.; DOI: https://doi.org/10.4150/KPMI.2013.20.1.019

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Abstract PDF: Ru films were successfully prepared by plasma-enhanced atomic layer deposition (PEALD) using Ru(EtCp)_2 and NH_3 plasma. To optimize Ru PEALD process, the effect of growth temperature, NH_3 plasma power and NH_3 plasma time on the growth rate and preferred orientation of the deposited film was systemically investigated. At a growth temperature of 270circC and NH_3 plasma power of 100W, the saturated growth rate of 0.038 nm/cycle was obtained on the flat SiO_2/Si substrate when the Ru(EtCp)_2 and NH_3 plasma time was 7 and 10 sec, respectively. When the growth temperature was decreased, however, an increased NH_3 plasma time was required to obtain a saturated growth rate of 0.038 nm/cycle. Also, NH_3 plasma power higher than 40 W was required to obtain a saturated growth rate of 0.038 nm/cycle even at a growth temperature of 270°C. However, (002) preferred orientation of Ru film was only observed at higher plasma power than 100W. Moreover, the saturation condition obtained on the flat SiO_2/Si substrate resulted in poor step coverage of Ru on the trench pattern with an aspect ratio of 8:1, and longer NH_3 plasma time improved the step coverage.

Coating Property of Hybrid Structured Photo-Electrode to Increase Dye-Sensitized Solar Cells Efficiency: Min-Hee Kim, Hyung-Woo Lee, Young-Keun Jeong; J Korean Powder Metall Inst. 2010;17(6):449-455.; DOI: https://doi.org/10.4150/KPMI.2010.17.6.449

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The hybrid structured photo-electrode for dye-sensitized solar cells was fabricated based on the composites of TiO_2 nanoparticles and nanowires. Three samples with different hybrid structures were prepared with 17 vol%, 43 vol%, and 100 vol% nanowires. The energy conversion efficiency was enhanced from 5.54% for pure nanoparticle cells to 6.01% for the hybrid structure with 17 vol% nanowires. For the hybrid structured layers with high nanowires concentration (43 vol% and 100 vol%), the efficiency decreased with the nanowire concentration, because of the decrease of specific surface area, and of thus decreased current density. The random orientations of TiO_2 nanowires can be preserved by the doctor blade process, resulted in the enhanced efficiency. The hybrid structured TiO_2 layer can possess the advantages of the high surface area of nanoparticles and the rapid electron transport rate and the light scattering effect of nanowires.

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N-Doped ZnO Nanoparticle-Carbon Nanofiber Composites for Use as Low-Cost Counter Electrode in Dye-Sensitized Solar Cells
하림 안, 효진 안
Korean Journal of Materials Research.2014; 24(10): 565~571. CrossRef

The Effect of Electrical Characteristics and Electrode Shape on Alignment of Multi-walled Carbon Nanotubes: Se-Hun Kwon, Young-Keun Jeong, Chang-Sik Jung, Myung-Chang Kang, Hyung-Woo Lee; J Korean Powder Metall Inst. 2010;17(4):326-335.; DOI: https://doi.org/10.4150/KPMI.2010.17.4.326

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Abstract PDF: In this paper, the effect of electrical characteristics and electrode shape on the alignment and attachment of multi-walled carbon nanotubes (MWNTs) has been studied. The attraction and alignment of MWNTs between the gaps has been investigated by applying electric field which is called electrophoresis and dielectrophoresis. According to the frequency of electric field, positive or negative dielectrophoretic force can be determined. The concentration of MWNTs solution was 5;µg/ml, and a droplet of 1.0sim1.5;µl was dropped between two electrodes. Through the repeated experiments, the optimal electrical conditions for aligning and attaching MWNTs in the desired places were obtained. Since the frequency range of 100 kHz~10 MHz generated positive dielectrophoretic force, MWNTs were attracted and aligned between the gaps with this frequency range. For generating enough force to attract MWNTs, the appropriate voltage range was 0.3sim1.3;V_rms/µm. Furthermore, the effect of electrode shape on the alignment of MWNTs was investigated. A single MWNT attachment was accomplished on the round shaped with 70% yield.

Characteristics of Micro EDM using Wire Electrical Discharge Grinding for Al₂O₃/CNTs Hybrid Materials: Hyun-Seok Tak, Jong-Hun Kim, Han-Suk Lim, Choon-Tae Lee, Young-Keun Jeong, Myung-Chang Kang; J Korean Powder Metall Inst. 2010;17(4):319-325.; DOI: https://doi.org/10.4150/KPMI.2010.17.4.319

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Electrical discharge machining (EDM) is an attractive machining technique but it requires electrically conductive ceramic materials. In this study, Alumina matrix composites reinforced with CNTs were fabricated through CNT purification, mixing, compaction and spark plasma sintering (SPS) processes. Al_2O_3 nanocomposites with the different CNT concentrations were synthesized. The mechanical and electrical characteristics of Al_2O_3/CNTs composites were examined in order to apply the materials to the EDM process. In addition, micro-EDM using wire electrical discharge grinding (WEDG) was conducted under the various EDM parameters to investigate the machining characteristics of machined hole by Field Emission Scanning Electron Microscope (FE-SEM). The results show that Al_2O_3/CNTs 10%Vol. was more suitable than the other materials because high conductivity and large discharge energy caused violent sparks resulting in bad machining accuracy and surface quality.

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Development of Vibration Assisted Hybrid Femtosecond Laser Ultra-precision Machining System and Cu-Zn alloy Application
Won-Suk Choi, Ji-Wook Yoon, Sung-Hak Cho, Myung-Chang Kang
Journal of Korean Powder Metallurgy Institute.2013; 20(4): 308. CrossRef
Machinability Evaluation of Hybrid Ti2Ceramic Composites with Conductivity in Micro Electrical Discharge Drilling Operation
Jae-Young Heo, Young-Keun Jeong, Myung-Chang Kang, Ahmed Busnaina
Journal of Korean Powder Metallurgy Institute.2013; 20(4): 285. CrossRef

Performance Evaluation on the Endmill of High Speed Machining for Selection of Tungsten Carbide (WC-Co) Material: Dong-Hee Kwon, Jeong-Suk Kim, Min-Wook Kim, Young-Keun Jeong, Myung-Chang Kang; J Korean Powder Metall Inst. 2008;15(5):359-364.; DOI: https://doi.org/10.4150/KPMI.2008.15.5.359

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To satisfy the demand of higher cutting performance, mechanical properties with tungsten carbide (WC-Co) tool materials were investigated. Hardness and transverse rupture strength with WC grain size, Co content and density were measured. Compared to H, K, and S manufacture maker as tungsten carbide (WC-Co) tool materials were used for high-speed machining of end-milling operation. The three tungsten carbide (WC-Co) tool materials were evaluated by cutting of STD 11 cold-worked die steel (HRC25) under high-speed cutting condition. Also, tool life was obtained from measuring flank wear by CCD wear measuring system. Tool dynamometer was used to measure cutting force. The cutting force and tool wear are discussed along with tool material characteristics. Consequently, the end-mill of K, H manufacture maker showed higher wear-resistance due to its higher hardness, while the S maker endmill tool showed better performance for high metal removal.

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Tool Wear Characteristics of Tungsten Carbide Implanted with Plasma Source Nitrogen Ions in High-speed Machining
Sung-Ho Park, Duck Hyun Wang
Journal of the Korean Society of Manufacturing Process Engineers.2022; 21(5): 34. CrossRef

Laser Microfabrication for Silicon Restrictor: Kwang-Ryul Kim, Young-Keun Jeong; J Korean Powder Metall Inst. 2008;15(1):46-52.; DOI: https://doi.org/10.4150/KPMI.2008.15.1.046

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Abstract PDF: The restrictor, which is a fluid channel from a reservoir to a chamber inside a thermal micro actuator, has been fabricated using ArF and KrF excimer lasers, Diode-Pumped Solid State Lasers (DPSSL) and femtosecond lasers for a feasibility study. A numerical model of fluid dynamics for the actuator chamber and restrictor is presented. The model includes bubble formation and growth, droplet ejection through nozzle, and dynamics of fluid refill through the restrictor from a reservoir. Since an optimized and well-fabricated restrictor is important for a high frequency actuator, some special beam delivery setups and post processing techniques have been researched and developed. The effects of variations of the restrictor length, diameter, and tapered shapes are simulated and the results are analyzed to determine the optimal design. The numerical results of droplet velocity and volume are compared with the experimental results of a cylindrical-shaped actuator. It is found that the micro actuators having tapered restrictors show better high frequency characteristics than those having a cylindrical shape without any notable decrease of droplet volume. The laser-fabricated restrictors demonstrate initial feasibility for the laser direct ablation technique although more development is required.

Research and Development of Hybrid Materials: Young-Keun Jeong, Myung-Chang Kang, Kwang-Ho Kim; J Korean Powder Metall Inst. 2007;14(1):1-7.; DOI: https://doi.org/10.4150/KPMI.2007.14.1.001

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Effect of Casting Speed on Microstructure and Mechanical Properties of Al-Mg-Si/Al Hybrid Material by Duo-Casting
Sung Jin Park, Jun-Young Suh, Hee-Kwon Lee, Si Young Chang
Korean Journal of Materials Research.2020; 30(3): 111. CrossRef
Fabrication of Ultra Fine Grained Molybdenum and Mechanical Properties
Se-Hoon Kim, Young-Ik Seo, Dae-Gun Kim, Myung-Jin Suk, Young-Do Kim
Journal of Korean Powder Metallurgy Institute.2010; 17(3): 235. CrossRef

Effect of Sintering Temperature on Microstructure and Mechanical Properties of Cu Particles Dispersed Al₂O₃ Nanocomposites: Young-Keun Jeong, Sung-Tag Oh, Yong-Ho Choa; J Korean Powder Metall Inst. 2006;13(5):366-370.; DOI: https://doi.org/10.4150/KPMI.2006.13.5.366

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Abstract PDF: The microstructure and mechanical properties of hot-pressed Al_2O_3/Cu composites with a different sintering temperature have been studied. The size of matrix grain and Cu dispersion in composites increased with increase in sintering temperature. Fracture toughness of the composite sintered at high temperature exhibited an enhanced value. The toughness increase was explained by the thermal residual stress, crack bridging and crack branching by the formation of microcrack. The nanocomposite, hot-pressed at 1450°C, showed the maximum fracture strength of 707 MPa. The strengthening was mainly attributed to the refinement of matrix grains and the increased toughness.

Fabrication of Ag doped Hydroxyapatite and its Antimicrobial Effects with the Particle Size: Kyung-Sik Oh, Kyung-Ja Kim, Young-Keun Jeong; J Korean Powder Metall Inst. 2001;8(3):192-196.

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Abstract PDF: Ag doped Hydroxyapatite powder in nano-scale was successfully synthesized either by co-precipitation or by ion exchange route. The fabricated powder was successfully dispersed through freeze drying due to the prevention of secondary particles. The antimicrobial effects of nano-HAp against E.coli was superior to micron ones not only in its strength but also in duration.

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