• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.731-732
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• 2006

Recently warm compaction techniques are focused on and commercialization of one high-density compaction process in the P/M industry. Another development is a new SEGLESS using a developed lubricant that reduces ejection force at room temperature compaction. It is possible to achieve high-density by reducing lubricant amount. In this paper we confirmed that green density was $7.35g/cm^3$ at 686MPa of compaction pressure when the new SEGLESS was applied to relatively lower temperature warm compaction process, such as $80^{\circ}C$.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.395-399
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• 1999

MgO/metal nanocomposite powder mixtures were prepared by solution chemical processes to obtain suitable structure for ceramic/metal nanocomposites. Nickel or cobalt nitrate, as a source of metal dispersion, was dissolved into alcohol and mixed with magnesia powder. After calcined in air, these powders were reduced by hydrogen. Densified nanocomposites were successively obtained by Pulse Electric Current Sintering (PECS) process. The dispersed metal partical size depended on temperature and time in calcination and reduction processes. The phase analyses in the synthesized powders as a functioni of temperature were tracked using a dynamic high temperature X-ray diffractioni (HTXRD) system. Phase and crystallite size analyses were done using X-ray diffractioni and TEM. The MgO/metal nanocomposites were successfully fabricated, and ferromagnetic responses with enhanced coercive force were also investigated for these composites.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.5 s.176
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• pp.1146-1154
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• 2000

Fatigue strength of NiAl and Ni$_3$Al particulate reinforced aluminum alloy composites fabricated by the diecasting method was examined at room and elevated temperatures. The results were compared wit h that of SiC particulate reinforced one. The particulate reinforced composites showed some improvement in the static and fatigue strength at elevated temperatures when compared with that of Al alloy. The composites reinforced by intermetallic compound particles showed good fatigue strengths at elevated temperatures especially $Ni_3AI_{p}/Al$ alloy composite showed good fatigue limit up to high temperature of 30$0^{\circ}C$. Adopting intermetallic compound particle as a reinforcement phase, it will be possible to develop MMC representing better fatigue property at elevated temperature.

• Progress in Superconductivity and Cryogenics
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• v.15 no.4
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• pp.48-52
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• 2013

This paper compares the features of second generation (2G) High Temperature Superconducting (HTS) field coil with those of magnesium diboride ($MgB_2$) field coil for a 10 MW class superconducting generator. Both coils can function effectively in their respective magnetic flux density range: 10-12 T for 2G HTS field coil, 2 T for $MgB_2$ superconducting field coil. Even though some leading researchers have been developing 10 MW class superconducting generator with 2G HTS field coil, other research groups have begun to focus on $MgB_2$ wire, which is more economical and suitable for mass production. However 2G HTS wire is still appealing in functions such as in-field property and critical temperature, it shows higher in-field property and critical temperature than $MgB_2$ wire.

• Journal of Advanced Marine Engineering and Technology
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• v.13 no.2
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• pp.64-77
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• 1989

In this study, the experiments were carried out for the purpose of establishment of aluminium cementation to steel surface by diffusible heat treatment after making the coated film onto the substrate by arc spray method. Also, the microstructure and mechanical properties of the cementation layer produced by this study were inspected for various heat treatment and spraying conditions. Main results obtained are as follow ; 1. The coating film characteristics which have excellent errosion-resistance, high temperature oxidation-resistance are obtained by aluminium penetration heat treatment after making the sprayed aluminum coating film onto the steel substrate. 2. Aluminium diffusion penetration takes place at higher temperature than 660.deg.C, and the more heat treatment time and the higher heat treatment temperature adopted, the deeper diffusion layer obtained. 3. Insert gas arc spraying using argon gas as the carrier gas higher improvement of mechanical property than that of compressed air environment. 4. The coating film characteristics appeared to be improvement of adhesive property, porosity plugging effect by heat treatment in air environment.

• Applied Science and Convergence Technology
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• v.26 no.6
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• pp.214-217
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• 2017

AlSb is a promising material for optical devices, particularly for high-frequency and nonlinear-optical applications. We report the effect of growth temperature on structural properties of AlSb grown on GaAs substrate. In particular we studied the surface of AlSb with the growth temperature by atomic force microscopy, and concluded that optimized growth temperature of AlSb is $530^{\circ}C$. We also show the result of real-time monitoring of AlSb growth by in situ ellipsometry. The results of the structural study are good agreement with the previous reported ellipsometric data.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.12
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• pp.25-32
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• 2010

Compared to general lighting method, the lighting system that uses optic fiber can provide only the visible light of good quality to subject by eliminating ultraviolet ray and infrared ray. Thanks to this merit, it is possible to prevent the hard phenomenon of subject caused by ultraviolet ray and infrared ray and to provide the agreeable light environment. This study developed indoors illumination system of high color rendering on the basis of plastic optic fiber with excellent optical property and processing to substitute halogen lamp which has been used for excellent color rendering in spite of low efficiency and short life. Producing pilot product of the designed illumination system and evaluating the property of electric and optical property, ultraviolet ray radiation quantity and temperature property, this study verified the excellence of suggested lighting system of plastic optic fiber.

• Korean Journal of Materials Research
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• v.15 no.1
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• pp.19-24
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• 2005

For the good combination of high-temperature strength, toughness and creep property, $9-12\%$ chromium steels are often used for gas turbine compressors, steam turbine rotors, blade and casing. In this study, the correlation of microstructural evolution and mechanical properties was investigated fur the specimens heat-treated at 600, 650 and $700^{\circ}C$ for 1000, 3000 and 5000 hrs. The microstructure of as-received specimen was tempered martensite with a high dislocation density, small sub-grains and fine secondary phase such as $M_23C_6$. Aging for long-time at high temperature caused the growth of martensite lath and the decrease of dislocation density resulting in the decrease in strength. However, the evolution of secondary phases had influence on hardness, yield strength and impact property. In the group A specimen aged at $600^{\circ}C\;and\;650^{\circ}C$, Laves phase was observed. The Laves phase caused the increase of the hardness and the decrease of the impact property. In addition, the abrupt growth of secondary phases caused decrease of the impact property in both A and B group specimens.

• Journal of Korea Foundry Society
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• v.40 no.4
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• pp.118-127
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• 2020

Microstructural evolution during a heat treatment and high-temperature tensile properties have been investigated in conventionally cast CM247LC. In as-cast specimens, MC carbides with high amounts of Ta, Ti, Hf, and W were found to exist in the interdendritic regions, and γ' was observed in the form of cubes and octocubes prior to decomposition into cubes. In the heat-treated condition, some portion of eutectic γ-γ' remained, and uniform cubic γ' was observed in both interdendritic regions and dendrite core. Three types of carbides with different stoichiometries and compositions were found at the grain boundaries. MC carbides with high Hf contents were observed in the vicinity of eutectic γ-γ'. The highest tensile strength value was found at 750℃, whereas the greatest ductility appeared at 649℃. The effect of the temperature on the tensile properties was closely related to the dislocation structure. With increase in the test temperature, the density of dislocations inside γ' decreased, whereas that in the γ matrix increased. Stacking faults generated in γ' at 750℃ had a strengthening effect, whereas thermally activated dislocation motion at a high temperature was considered to have the opposite effect.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.383-386
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• 2008

Magnesium alloy sheets have been extending their field of applications to automotive and electronic industries taking advantage of their excellent light weight property. In addition to their excellent light property, magnesium alloys have several other advantages: high specific strength, good welding capability and corrosion resistance. Taking advantage of these benefits, magnesium alloys have also been substituting the polymeric materials in the electronic devices industries. In sheet metal forming application with magnesium alloys, the lower formability and high springback due to the lower elastic property (Young's modulus=45 GPa) at room temperature are major hurdles by which magnesium alloys have limited applications. In this study, commercial notebook case was adopted as the benchmark model, and then design parameters and process conditions are analyzed by the finite element simulation and physical try-outs.