• Journal of the Korean Society for Heat Treatment
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• v.9 no.1
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• pp.27-33
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• 1996

Metallographic observation was carried out by scanning and transmission electron microscopy to evaluate microstructural characteristics of partially austenitized and isothermally transformed 1.0C-1.5Cr bearing steel. It was observed that lower bainite formed in the local region of specimen partially austenitized and isothermally held at $250^{\circ}C$ for 1/3 hr and formed in almost all area of the specimen isothermally held at $250^{\circ}C$ for 2 hrs. Lower bainitic carbides with midrib was also observed in the specimen partially austenitized and isothermally held at $250^{\circ}C$ for 4 hrs. Midrib was nearly carbide-free region and thicker in the vicinity of spherical carbides than the other region. Lengthening speed of lower bainitic carbides was remarkabey increased at isothermal holding time ranging from 2 hrs to 4 hrs.

• Journal of Surface Science and Engineering
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• v.32 no.2
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• pp.100-108
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• 1999

The microstructure and corrosion properties of Al-Si diffusion coated PWA1426 alloy have been investigated. Experimental variables are included temperatures of heat-treatment and coating thickness. The microstructure of coated layer and corrosion properties were analysed by SEM, EDS and hot corrosion test. Two major processes have been found to contribute to microstructural changes in the coating. These are, firstly, the transformation of the NiAl to other $Ni_2Al_3$-based phase and secondly, the precipitation of Cr containing phases. Specimens heat treated at $1080^{\circ}C$ showed superior corrosion resistance to heat treated at $880^{\circ}C$. These increase in life was attributed to the transformation of NiAl and increased coating thickness of PWA1426 alloy.

• Annual Conference of KIPS
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• 2022.05a
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• pp.689-690
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• 2022

동영상 공유 플랫폼의 유저가 늘어남에 따라 영상을 통해 다양한 정보가 공유된다. 하지만 다양한 정보들이 영상으로 제한된 채 사용되고 있다. 이러한 제한점의 개선을 위하여 우리는 유튭콕을 기획하였다. 유튭콕 애플리케이션은 유튜브의 영상 정보를 기반으로 하는 위치 정보 마킹 및 공유 서비스이다. 유튭콕을 통해 관심이 있는 동영상의 정보를 받아와 지도를 생성하여 위치 정보를 가시적으로 확인할 수 있다. 또한 지도 공유 기능을 통해 타 유저와의 공유 서비스를 제공한다.

• Korean Journal of Materials Research
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• v.11 no.12
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• pp.1047-1051
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• 2001

Purity tantalum powder has been produced by sodium reduction of potassium tantalum fluoride($K_2TaF_7$)in a stainless steel bomb. The influence of experimental variable, such as excess of reductant and temperature of reduction on the yield and quality of the Ta powder has been studied. The excesses of reductant were varied from -20%, -10%, 0%, 5%, 10%, 20%. When -20% excess of sodium was used, the un-reacted sodium remained in the reacted product. The yield of 81% of Ta powder has been achieved by reducing 50g of$K_TaF_7$with 5% sodium in excess of stoichiometric amount in presence of 16.8g of sodium chloride in the charge at a reduction temperature of$905{\circ}C$. The proportion of fine fraction(~325mesh) decreased appreciably with the increase of sodium excess, and the yield of tantalum powder improved from 65% to 94%. The average particle size of Ta Powder is improved from 3 microns to 4 microns in the 5% excess sodium.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.4
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• pp.1971-1982
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• 2014

The purpose of the this study is to analyze what business value orientations are more effective on the enhancement of productivity and performance indexes of IT companies. Especially we are interest in the moderate effect of business types such as IT manufacturing, IT services, and non-IT manufacturing companies. The empirical test results was somehow different from the theoretical researches. Customer orientation affects productivity directly and performance indexes indirectly. Whereas, technology innovation orientation didn't affects productivity and performance indexes directly, except IT services companies. Corporate social responsibility affects performance indexes directly, but not productivity. We could conclude that the type of business is an important moderator between business value orientations and enterprise performance factors.

• Korean Journal of Materials Research
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• v.26 no.8
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• pp.444-448
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• 2016

In this study, the recently developed Al 2013 alloy was T8-tempered and, to improve the strength and corrosion-resistance, slight amounts of Zr of 0.2 wt% and 0.5 wt%, respectively, were added and the mechanical properties were analyzed. For microstructure and precipitate analysis, OM observation, XRD analysis, and TEM analysis were performed, and for the mechanical property analysis, hardness and tensile strength tests were done. Also, in order to determine the corrosion rate according to the Zr content, a potentiodynamic polarization test was performed and the properties were compared and analyzed. The size of the precipitate varied with the content of Zr and was finest at Zr content of 0.2 wt%; it grew larger at 0.5 wt%, at which point the hardness value accordingly showed the same trend. On the other hand, as calculated from the aspect of chemical bonding among atoms, it was confirmed that the tensile strength and the corrosion-resistance increased with the same trend.

• Journal of Powder Materials
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• v.10 no.6
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• pp.395-405
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• 2003

In the conventional metallothermic reduction (MR) process for obtaining tantalum powder in batch-type operation. it is difficult to control morphology and location of deposits. On the other hand, a electronically mediated reaction (EMR) process is capable to overcome these difficulties and has a merit of continuous process, but it has the defect that the reduction yield is poor. MR-EMR combination process is a method that is able to overcome demerits of MR and EMR process. In this study, a MR-EMR combination process has been applied to the production of tantalum powder by sodium reduction of $K_2$TaF$_{7}$. The total charge passed through external circuit and average particle size (FSSS) were increased with increasing reduction temperature. The proportion of fine particle (-325 mesh) was decreased with increasing reduction temperature. The yield was improved from 65% to 74% with increasing reduction temperature. Considering the charge, impurities, morphology, particle size and yield, an reduction temperature of 1,123 K was found to be optimum temperature for MR-EMR combination process.

• 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.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.3
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• pp.186-191
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• 1998

An oxidation behavior of 304 and 316 stainless steels were studied in dry air. After solution treatment, specimens were polished up to $1{\mu}m$ $A1_2O_3$ grade and then subjected to oxidation treatment in dry air at $800^{\circ}C{\sim}1200^{\circ}C$. The oxidation behavior between matrix and oxide scale was analyzed with SEM, EDS and XRD. When oxidation treatment was conducted at $1200^{\circ}C$, large thickness of Fe oxide scale was formed on top of surface and fine $(Cr,Fe)_2O_3$ oxide film was formed below it. Cr rich zone existed at interface between metal and $(Cr,Fe)_2O_3$ oxide layer, and it was believed that this zone acted as obstacle to oxidation. Most of Ni was detected at the interface between metal and $(Cr,Fe)_2O_3$ and also detected at the interface between $Fe_2O_3$ and $(Cr,Fe)_2O_3$.

• Korean Journal of Materials Research
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• v.25 no.11
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• pp.642-646
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• 2015

Super alloys, which can be divided into three categories, i.e. Ni-base, Co-base, and Fe-base alloys, are widely used for high temperature applications. Since superalloys contain many alloying elements and precipitates, their chemistry and processing parameters need to be carefully designed. In this study, we designed a new Ni alloy to prevent corrosion due to water vapor and gases at high temperatures. The new alloy was designed using the theoretical value of the resulting energy electronic state calculation($DV-X{\alpha}$ method). The components that were finally used were Cr, Mo, and Ti, with Ni as a base. For these alloys, elements were selected in order to compare their values with that of the average theoretical basis for an Inconel 625 alloy. Finally, two kinds of Ni alloy were designed: Ni-28Cr-4Mo-2Ti and Ni-20Cr-10Mo-1Ti.