• Composites Research
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• v.19 no.2
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• pp.7-12
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• 2006

Graphite particle/carbon fiber hybrid conductive polymer composites were fabricated by the compression molding technique. Graphite particles were mixed with an epoxy resin to impart the electrical conductivity in the composite materials. In this study, graphite reinforced conductive polymer composites with high filler loadings were manufactured to accomplish high electrical conductivity above 100S/cm. Graphite particles were the main filler to increase the electrical conductivity of composites by direct contact between graphite particles. While high filler loadings are needed to attain good electrical conductivity, the composites becomes brittle. So carbon fiber was added to compensate weakened mechanical property. With increasing the carbon fiber loading ratio, the electrical conductivity gradually decreased because non-conducting regions were generated in the carbon fiber cluster among carbon fibers, while the flexural strength increased. In the case of carbon fiber 20wt.% of the total system, the electrical conductivity decreased 27%, whereas the flexural strength increased 12%.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.2
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• pp.93-100
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• 2006

Building materials are trending toward environmental materials nowadays and the market share of those is growing. So those researches and developments for environmental property are proceeding now. The main properties of environmental products are far infrared emission, negative ion emission, electro magnetic wave shielding, and anti fungus, these products are used with shape of mortar, and spray on the finish material. But There are not much researches for the concrete, main material in construction field, with those functional properties. So in this research we evaluated slump, compressive strength and air content as basic properties for concrete using functional materials of sericite, wood pattern sand stone, carbon black and nanometric silver solution and functional properties like far infrared emission, negative ion emission, electro magnetic wave shielding, and anti fungus. The results were as follows. The most useful material in the functional materials was carbon black. Sericite and nanometric silver solution had a little effect on functional property, so it was difficult to apply to concrete, and wood pattern sand stone had a high functional property but low compressive strength, can be applied to a factory product. Anti fungus of the concrete using nanometric silver solution was not clear but if those specimens were aged in $CO_2$ gas for a long time it might apparent.

• Korean Journal of Materials Research
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• v.19 no.11
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• pp.619-624
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• 2009

Titanium alloys have been attractive due to a high ratio of strength to weight as well as good corrosion resistance. However, strengthening causes a decrease in ductility in Ti alloys, as is usual in other alloys. For enhanced strength without ductility reduction, grain refinement and tensile properties were investigated as functions of thickness reduction of cold rolling and annealing condition in Ti-15V-3Cr-3Sn-3Al alloy with a ${\beta}$ single phase. The average grain size of the specimen, which was cold-rolled by 90% and annealed at 700$^{\circ}C$ for 5 min, was decreased to approximately 19 ${\mu}m$. The grain refinement of 63 μm to 19 ${\mu}m$ increased yield stress by 90 MPa without a significant decrease in total elongation. The Ti-15-3 alloy exhibited very low work hardening during tensile test at a crosshead speed of 2 mm/min. This result was discussed based on dynamic recovery associated with dislocation annihilation in grain boundaries.

• Korean Journal of Materials Research
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• v.24 no.4
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• pp.175-179
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• 2014

Ti and Ti alloys have been extensively used in the medical and dental fields because of their good corrosion resistance, high strength to density ratio and especially, their low elastic modulus compared to other metallic materials. Recent trends in biomaterials research have focused on development of metallic alloys with elastic modulus similar to natural bone, however, many candidate materials also contain toxic elements that would be biologically harmful. In this study, new Ti based alloys which do not contain the toxic metallic components were developed using a theoretical method (DV-$X{\alpha}$). In addition, alloys were developed with improved mechanical properties and corrosion resistance. Ternary Ti-Ag-Zr alloys consisting of biocompatible alloying elements were produced to investigate the alloying effect on microstructure, corrosion resistance, mechanical properties and biocompatibility. The effects of various contents of Zr on the mechanical properties and biocompatibility were compared. The alloys exhibited higher strength and corrosion resistance than pure Ti, had antibacterial properties, and were not observed to be cytotoxic. Of the designed alloys' mechanical properties and biocompatibility, the Ti-3Ag-0.5Zr alloy had the best results.

• Progress in Superconductivity and Cryogenics
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• v.19 no.2
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• pp.53-57
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• 2017

In superconducting power devices including power cables in which high temperature superconducting (HTS) tapes are utilized, a reliable electrical insulation should be achieved for its maximum performance. For an efficient design of HTS superconducting devices, a comparative evaluation of the mechanical and thermal propperties for various insulation materials at cryogenic temperatures is required. Especially, in the process of the property evaluation of the sheet-shaped insulation materials, anisotropy according to the machining direction should be considered because the mechanical and thermal properties are significantly influenced by the sample orientation. In this study, the cryogenic thermal and mechanical properties of various insulation material sheets such as PPLP, Cryoflex, Teflon, and Kapton were determined considering sample orientation. All samples tested at cryogenic temperature showed significantly higher tensile strength as compared with that of room temperature. The ultimate tensile strength at both temperature conditions significantly depended upon the sample orientation. The thermal properties of the insulation materials exhibited a slight difference among samples depending on the orientation: for the PPLP and Cryoflex, the CD orientation showed larger thermal contraction up to 77 K as compared to the MD one. MD samples in PPLP and Cryoflex showed a lower CTE and thermal contraction which made it more promising as an insulation material due to its comparable CTE with HTS CC tapes.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.25-28
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• 2003

Carbon nanotubes(CNTs), since their first discovery, have been considered as new promising materials in various fields of applications including field emission displays, memory devices, electrodes, NEMS constituents, hydrogen storages and reinforcements in composites due to their extra-ordinary properties. The carbon nanotube reinforced nanocomposites have attracted attention owing to their outstanding mechanical and electrical properties and are expected to overcome the limit of conventional materials. Various application areas are possible for carbon nanotube reinforced nanocomposites through the functionalization of carbon nanotubes. Carbon nanotube reinforced polymer matrix nanocomposites have been fabricated by liquid phase process including surface functionalization and dispersion of CNTs within organic solvent. In case of carbon nanotube reinforced polymer matrix nanocomposites, the mechanical strength and electrical conducting can be improved by more than an order of magnitude. The carbon nanotube reinforced polymer matrix nanocomposites can be applied to high strength polymers, conductive polymers, optical limiters and EMI materials. In spite of successful development of carbon nanotube reinforced polymer matrix nanocomposites, the researches on carbon nanotube reinforced inorganic matrix nanocomposites show limitations due to a difficulty in homogeneous distribution of carbon nanotubes within inorganic matrix. Therefore, the enhancement of carbon nanotube reinforced inorganic nanocomposites is under investigation to maximize the excellent properties of carbon nanotubes. To overcome the current limitations, novel processes, including intensive milling process, sol-gel process, in-situ process and spark plasma sintering of nanocomposite powders are being investigated. In this presentation, current research status on carbon nanotube reinforced nanocomposites with various matrices are reviewed.

• Journal of the Korean Society for Heat Treatment
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• v.26 no.6
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• pp.279-287
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• 2013

Oxide Dispersion Strengthened (ODS) Fe with $Al_2O_3$ dispersoid was successfully produced by reactive milling with a mixture of Fe, $Fe_3O_4$ (Magnetite), $Fe_2O_3$ (Hematite) and Al reactants at cryogenic temperature. The milled powders were consolidated by Vacuum Hot Press (HP) at 1323 K, and the consolidated materials were characterized by Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM), and Energy Dispersive Spectroscopy (EDS); the yield strength and the hardness of the consolidated materials were determined by compressive test and Vickers hardness test at room temperature. The grain size of the materials was estimated by X-ray Diffraction technique using the scherrer's formula. The TEM observations showed that the microstructure was comprised with a mixture of nanocrystalline Fe matrix and $Al_2O_3$ nano-dispersoids with a bimodal size distribution; the 0.2% off-set yield strength of the materials was as high as $758{\pm}29$ MPa and the Vickers hardness was $358{\pm}2$. The effect of the cryogenic milling and addition of extra Fe powder was discussed on the suppression of MSR (Mechanically induced Self-sustaining Reaction) for the desired microstructural evolution of ODS alloys.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.3
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• pp.138-145
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• 2012

An ${\alpha}$-Ferrite (Fe) powder dispersed with 4 vol.% of $Al_2O_3$ was successfully produced by a simple miling at 210 K with a mixture of $Fe_2O_3$, Fe and Al ingredient powders, followed by 2 step high temperature consolidation: Hot Pressing (HP) at 1323 K and then Hot Isostatic Pressing at 1423 K. The microstructure of the consolidated material was characterized by standard metallographic techniques such as XRD (X-ray Diffraction), TEM and STEM-EDS. The results of STEM-EDS analysis showed that the HIPed materials comprised a mixture of pure Fe matrix with a grain size of ~20 nm and $Al_2O_3$ with a bimodal size distribution of extremely fine (~5 nm) and medium size dispersoids (~20 nm). The mechanical properties of the consolidated materials were characterized by compressive test and micro Vickers hardness test at room temperature. The results showed that the yield strength of the ODS (Oxide Dispersion Strengthened) Fe alloy are as much as $674{\pm}39$ MPa and the improvement of the yield strength is attributed to the presence of the fine $Al_2O_3$ dispersoid.

• International Journal of Automotive Technology
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• v.7 no.2
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• pp.209-216
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• 2006

A study has been conducted for an optimal processing and an apparatus for manufacturing a laser welded tube for one-body formed bumper beam. The tube dimensions used in calculation were the thickness of 1.4 mm, the diameter of 105.4 mm and the length of 2000 mm. The tube was formed of a cold rolled high strength steel plate(tensile strength of 600 MPa). The two-roll bending method was the optimal tube forming process in comparison with the UO-bending method, the bending method on the press brake, the multi-step continuous roll-forming method and the 3-roll bending method. Monitoring of the welding quality was conducted and the seam tracking along the butt-joint lengthwise to the tube axis was also examined. The longitudinal butt-joint was welded by using a $CO_2$ laser welding machine equipped with a seam tracker and a plasma sensor. The $CO_2$ laser tube welding machine could be used for precise seam tracking and real-time monitoring of the welding quality. As a result, the developed laser welded tube could be used for a one-body formed automobile bumper beam.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.480-481
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• 2006

The n-type $(95%Bi_2Te_3-5%Bi_2Se_3)$ compound was newly fabricated by gas atomization and hot extrusion, which is considered to be a mass production technique of this alloy. The effect of powder size on thermoelectric properties of 0.04% $SbI_3$ doped $95%Bi_2Te_3-5%Bi_2Se_3$ alloy were investigated. Seebeck coefficient $({\alpha})$ and Electrical resistivity $(\rho)$ increased with increasing powder size due to the decrease in carrier concentration by oxygen content. With increasing powder size, the compressive strength of $95%Bi_2Te_3-5%Bi_2Se_3$ alloy was increased due to the relative high density. The compound with ${\sim}300\;{\mu}m$ size shows the highest power factor among the four different powder sizes. The rapidly solidified and hot extruded compound using $200[\sim}300{\mu}m$ powder size shows the highest compressive strength.