Papers by Author: Jong Ho Kim

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Authors: Jong Ho Kim, Young Gu Kim, Hyeon Keun Lee, Do Kyung Kim
Abstract: The mechanical properties of brittle coating structures were characterized by various indentation techniques. The adhesion properties of the coatings were evaluated by in situ scratch and sphere indentation method. Physical vapor deposited TiN coatings on transparent substrates, sapphire, were scratched by diamond cone indenter and in situ observed through the transparent substrate. In situ scratch results reveal that the failure of coating is originated from the damage of the substrate and the plastic deformation of substrate is a primary factor for determining the adhesion breakage. The unique characterization technique for the strength measurement of brittle thin coating has been developed. The strength of the thin coating was evaluated by the sphere indentation on the trilayer structure. The CVD SiC coatings on graphite were characterized by the technique. It is concluded that the microstructure of SiC coatings influences the strength. In this paper, the various indentation technique were applied to evaluate the mechanical properties of TiN and SiC coatings and the effect of microstructure on the reliability of the brittle coating system was discussed.
Authors: Chul Seung Lee, Jong Ho Kim, Do Kyung Kim
Authors: Jong Ho Kim, Young Gu Kim, Do Kyung Kim, Kee Sung Lee, Soon Nam Chang
Abstract: Hertzian and explosive indentations were used to determine the damage behavior of SiC and Si3N4 ceramics. Specimens were selected with different microstructures. In order to observe the subsurface damaged zone, the bonded interface technique was adopted. It was found that the damage response depends strongly on the microstructure of ceramics. Examination of subsurface damage reveals a competition between brittle and quasiplastic damage mode: brittle fracture mode is dominant in fine grain microstructure; quasiplastic deformation occurs in coarse grain. Dynamic indentation induces subsurface yield zone which contains extensive micro-cracks. The role of microstructure on static and dynamic damage behavior are discussed in terms of the weakness of grain boundary and grain size.
Authors: Seung Hwan Jo, Jong Ho Kim, Do Kyung Kim
Abstract: Two kinds of nano crystalline Gd-doped CeO2 particles were successfully synthesized via glycine-nitrate combustion and neutral precipitation with subsequent hydrothermal crystallization. It was revealed that the surface modification of nano particles significantly affected sintering behaviors and resulting physical properties. Glycine/nitrate ratio was a key parameter to control the surface state of nano particles in the glycine-nitrate process, but, in the neutral precipitation process, the solvent was important. To obtain the GDC nano particles with chemically and physically favorable properties, the effect of the surface state of nano particles on the sintering behavior was discussed with consideration of aggregation property and surface-adsorbed substances on nano particles.
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