Papers by Author: In Bae Kim

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Authors: In Gon Kim, Yang Do Kim, In Bae Kim
Abstract: The effects of pre-strain and aging treatment on the mechanical properties of hot rolled steel sheet containing 1.0wt.%Cu were investigated. As the amount of pre-strain increased, the maximum hardness increased and the time to reach its peak hardness decreased. Tensile strength of 10% pre-strained steel was 600MPa. This value was about 150MPa higher than that of hot rolled steel. In case of 30% pre-strained steel, the strength was further increased to 657MPa. Such a strength increase was due to the strain hardening and enhanced precipitation reaction of Cu-clusters. TEM study revealed that fine Cu-clusters were uniformly dispersed throughout the grain. This means that the precipitation of Cu-clusters was mainly controlled by the vacancies introduced during the pre-straining process. The size of Cu-clusters was about 10~20nm at peak aged condition and they had spherical shape.
Authors: In Bae Kim, Yong Su Park, Kyung Hyun Kim, In Gon Kim
Abstract: Effects of Si and Cr additions on the fatigue properties of Al-Zn-Mg-Cu cast alloy were investigated by low and high cycle fatigue tests. It was found that in the low cycle fatigue test, fatigue life of base alloy showed the maximum value of 3,075 cycles, whereas in Si and Cr containing alloys, it was 2,993 and 1,413 cycles, respectively. The same trend was obtained in high cycle fatigue test, i.e., the fatigue strength in base alloy showed the highest value of 104MPa and decreased to 100MPa for Cr containing alloy and 81MPa for Si containing alloy. The fatigue ratio was about 0.20 for all three alloys. The tensile strength of base alloy also showed the maximum value of 513MPa, and decreased with the addition of Si and Cr to 400 and 500MPa, respectively. Metallographic observation revealed that the fatigue crack initiated at the surface and propagated along the grain boundary.
Authors: In Bae Kim, Kwang Nyeon Kim, Kyung Hyun Kim, In Gon Kim
Abstract: Effects of Si and Cr additions and aging treatment on the stress corrosion cracking(SCC) resistance of Al-Zn-Mg-Cu cast alloys were investigated by C-ring test and electrical conductivity measurement. The SCC resistance of Al-Zn-Mg-Cu cast alloys decreased in the order of Cr containing alloy, Si containing alloy and base alloy. The lowest electrical conductivity of Cr containing alloy exhibited the best SCC resistance and this is probably due to an improved corrosion resistance by forming a passive film on the surface. The over-aged alloys showed the better SCC resistance. This is due to the increased distance between coarse particles at grain boundary. The fracture mode of the alloy was confirmed as intergranular type and showed brittle fracture surface. The SCC mechanism of Al-Zn-Mg-Cu cast alloys was found to be the anodic dissolution model.
Authors: In Bae Kim, Jin Young Hong, Bong Gil Hong, Kyung Hyun Kim
Abstract: The precipitation behavior of Mg-Y-Nd-Zr alloy was investigated by using transmission electron microscopy. The precipitation sequence of Mg-Y-Nd-Zr alloy was confirmed as follows ; Supersaturated solid solution → β''→ β'→ β.The β'' phase was identified Mg3Nd having DO19 structure with the lattice constant of a=2aMg=0.64nm and c=cMg=0.52nm. The β' precipitate was identified as Mg12NdY having base centered orthorhombic structure with the lattice constants a, b and c of 0.64, 2.23 and 0.52 nm, respectively. The β phase was confirmed as equilibrium phase having the fcc structure with the lattice constant of a=2.22 nm.
Authors: Myoung Seok Sung, Yoon Bok Lee, Young Seok Kim, Young Mok Rhyim, Jin Chun Kim, In Bae Kim, Yang Do Kim
Abstract: CdSe nanoparticles with average particles size of ~ 3.4 nm were successfully prepared by the sonochemical reduction of a mixed solution of CdCl2, Na2SeSO3 and CH2CH2OH)2NH at room temperature. CdSe nanoparticles characterized by TEM, XPS and XRD analysis revealed the formation of high purity cubic phase CdSe nanoparticles with lattice constant of a=6.415Å. CdSe nanoparticles showed relatively large range of particle size distribution from 20 to 50 nm as the sonication time increased. UV-Vis absorption spectra showed a red-shift in the wavelength region of 545-590 nm as increasing sonication time due to the gradual growth of CdSe nanoparticles in the solution. This paper will mainly present the effects of ultrasonic irradiation on the formation and properties of CdSe nanoparticles.
Authors: Shin Ho Kim, Yoon Bok Lee, Seung Chan Cho, Young Mok Rhyim, Jin Chun Kim, Young Seok Kim, In Bae Kim, Yang Do Kim
Abstract: Cadmium selenide (CdSe) have been prepared by the reduction of mixed solution of cadmium chloride (CdCl2), sodium selenosulfate (Na2SeSO3) and diethanolamine ((CH2CH2OH)2NH) at temperatures of 80-200°C under Ar atmosphere. Characteristics of CdSe nanoparticles were analyzed using transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD) and UV-Vis absorption spectra. CdSe samples prepared at relatively low temperature of below 100°C showed cubic structure while samples synthesized at temperature above 100°C showed hexagonal phase. The increased reaction temperature caused the particle size increase as well as the agglomeration of particles to form a hollow sphere. UV-Vis absorption spectra also showed a red-shift as increasing reaction temperatures due to the gradual growth of CdSe nanoparticles in the solution. The relatively sharp absorption band from samples synthesized at 80 and 100°C can be attributed to homogeneous particle size distribution compared with those of prepared at elevated temperatures. This paper will mainly discuss the phase stability of CdSe nanoparticles as well as the hollow sphere formation.
Authors: Moon Hee Choi, Yoon Bok Lee, In Bae Kim, Young Seok Kim, Young Mok Rhyim, Jin Chun Kim, Yang Do Kim
Abstract: Cadmium selenide (CdSe) of hollow sphere with 30-50nm in diameter have been prepared form the mixed solution of cadmium chloride (CdCl2), sodium selenosulfate(Na2SeSO3) and ethylenediamine (H2NCH2CH2NH2) at room temperature. The hollow sphere of CdSe was characterized by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The molar ratio of EDA to Cd2+ ions in this system was important factor on controlled synthesis in the self-encapsulated morphology. Based on the observation on morphological difference with molar ratio of EDA to Cd2+ ion, the possible mechanism for the formation of CdSe hollow sphere was discussed.
Authors: Yang Ki Hyun, Soon Ho Won, Jae Ho Jang, In Bae Kim
Abstract: Evolution of microstructure due to service exposure to high temperature has a strong effect performance of heat resistant steels. In case of modified 9Cr-1Mo steels, precipitation of Fe2Mo-type laves phases and coarsening of M23C6-type carbides are the primary cause of degradation of mechanical properties such as creep resistance, tensile strength and toughness. Therefore creep tests have been carried out on modified 9Cr-1Mo steels to examine the effect of aging and stress on the creep strength. Additionally vibrating sample magnetometer is used to measure hysteresis loop.
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