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Shin, Keesam,Lee, Sunghak 대한금속재료학회 2003 METALS AND MATERIALS International Vol.9 No.6
This is a study on the fabrication of surface composites of SiC, TiC particulates, and AISI 304 substrate by high voltage electron beam irradiation. Using CaF2 powders as flux, two kinds of surface composites were fabricated for a comparative analysis of the microstructural modification and mechanical properties. Through the employed process, the powders and substrate surface were melted and surface composite layers were successfully formed in both cases. In the specimen fabricated with SiC powders, a volume fraction of Cr_(23)C_(6) particles (~22 vol.%) were homogeneously distributed along solidification cell boundaries. The large amount of Cr_(23)C_(6) particles in combination with solid solution hardening of Si in the matrix resulted in the improved hardness and wear resistance of the surface composite layer, that are 2 to 3 times those of the substrate. In the specimen fabricated with SiC and Ti+SiC powders, TiC and Cr_(23)C_(6) particles were precipitated without precipitation of SiC.
Cavity Formation Mechanism in Inert-Gas-Atomized Superalloy A-286
Shin, Keesam 국립7개대학공동논문집간행위원회 2001 공업기술연구 Vol.1 No.-
Cavity formation mechanism is that of great interest for the possibility of utilizing the cavities as a material strengthening elements and also for the application of the knowledge obtained to suppress the cavity formation upon radiation damage. In this study, the cavity formation mechanism is studied in the inert-gas-atomized superalloy A-286. The powders produced by IGA are rapidly solidified by the rapid heat extraction during atomization. This study focuses the effect solute atoms on the cavity formation.
Performance Evaluation of Textile-Based Electrodes and Motion Sensors for Smart Clothing
Gilsoo Cho,Keesam Jeong,Min Joo Paik,Youngeun Kwun,Moonsoo Sung IEEE 2011 IEEE SENSORS JOURNAL Vol.11 No.12
<P>Development of textile-based electrodes and motion sensors is one of the main issues of recent smart textile research utilizing electronic textiles. Electrocardiogram (ECG) electrodes have been developed by various textile technologies such as sputtering or electroless-plating on the fabric surfaces, and embroidering or knitting with stainless steel yarns. In addition, two types of motion sensors have also been developed using piezo-resistive textiles. They were fabricated by knitting and braiding. To examine the usability of the ECG electrode, waveforms of the conventional AgCl electrode, and the new electrodes developed in our lab were compared. It was found that electrodes using metallic embroidering are more efficient when its substrate was a metal blended fabric. The electrolessly Cu/Ni plated fabrics obtained the best conductivity in textile-based electrodes. The first motion-measuring textile-based sensor was used to predict and measure the changes in electric resistances that accompany the angle changes in the elbow joint. An advanced piezo-resistive textile by braiding showed more accurate resistance changes and also better durability. Changes in its electrical resistance were mapped to changes in its length extension. From the relationship between the extension and the electrical resistance, movement or posture of human body was detected.</P>
고에너지 전자빔 투사를 이용한 표면합금화 재료의 미세조직 연구
유정훈,신기삼,윤재홍,이찬규,허성강,오준철,이성학,어광준 국립7개대학공동논문집간행위원회 2002 공업기술연구 Vol.2 No.-
For determination of the mechanism of microstructural modification by surface alloying technique using high energy electron beam (HEEB), surface alloys of carbon steel with TiC, TiB_2 and VC were fabricated and their microstructures were analyzed using optical microscope, XRD (X-ray diffractometer), and SEM (scanning electron microscope). The surface regions of TiC and VC surface alloy consists of 1) melted, 2) interface, and 3) heat affected regions. In the TiC surface alloy precipitates of large primary and fine eutectic TiC were observed. In TiB_2 surface alloy, neither fine precipitates were present nor the TiB_2 shape was changed from the original particles, which was attributed to the high melting temperature of TiB_2. Among the three surface alloys studied, the melted region hardness of VC surface alloy was the highest.
Effect of Shot Peening on Microstructural Evolution of 500-7 Ductile Cast Iron
Zhang, Yubing,Shin, Keesam Korean Society of Microscopy 2018 Applied microscopy Vol.48 No.3
Ductile cast iron is widely used for many automotive components due to its high wear resistance and fatigue resistance in addition to the low cost of fabrication. The improvement of wear resistance and fatigue properties is key to the life time extension and performance increase of the automobile parts. Surface nanocrystallization is a very efficient way of improving the performance of materials including the wear- and fatigue-resistance. Shot peening treatment, as one of the popular and economic surface modification methods, has been widely applied to various materials. In this study, ductile cast iron specimens were ultrasonic shot peening (USP) treated for 5 to 30 min using different ball size. The microstructures were then microscopically analyzed for determination of the microstructural evolution. After the USP treatment, the hardness of pearlite and ferrite increased, in which ball size is more effective than treatment time. With USP treatment, the graphite nodule count near the surface was decreased with grain refinement. The lager balls resulted in an increased deformation, whereas the smaller balls induced more homogenously refined grains in the deformation layer. In addition, formation of nanoparticles was formed in the surface layer upon USP.
Development of High-Temperature Solders: Contribution of Transmission Electron Microscopy
Bae, Jee-Hwan,Shin, Keesam,Lee, Joon-Hwan,Kim, Mi-Yang,Yang, Cheol-Woong Korean Society of Microscopy 2015 Applied microscopy Vol.45 No.2
This article briefly reviews the results of recently reported research on high-temperature Pb-free solder alloys and the research trend for characterization of the interfacial reaction layer. To improve the product reliability of high-temperature Pb-free solder alloys, thorough research is necessary not only to enhance the alloy properties but also to characterize and understand the interfacial reaction occurring during and after the bonding process. Transmission electron microscopy analysis is expected to play an important role in the development of high-temperature solders by providing accurate and reliable data with a high spatial resolution and facilitating understanding of the interfacial reaction at the solder joint.
Transmission Electron Microscopy Specimen Preparation of Delicate Materials Using Tripod Polisher
Cha, Hyun-Woo,Kang, Min-Chul,Shin, Keesam,Yang, Cheol-Woong Korean Society of Microscopy 2016 Applied microscopy Vol.46 No.2
Transmission electron microscopy (TEM) is a powerful tool for analyzing a broad range of materials and provides localized information about the microstructure. However, the analysis results are strongly influenced by the quality of the thin foil specimen. Sample preparation for TEM analysis requires considerable skill, especially when the area of interest is small or the material of interest is difficult to thin because of its high hardness and its mechanical instability when thinned. This article selectively reviews recent advances in TEM sample preparation techniques using a tripod polisher. In particular, it introduces two typical types (fl at type and wedge type) of TEM sample preparation and the benefits and drawbacks of each method; finally, a method of making better samples for TEM analysis is suggested.