Papers by Author: Dong Hyuk Shin

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Authors: Dong Hyuk Shin, Jong Ryoul Kim, Yong Jun Oh, Kyung Tae Park
Authors: Young Gun Ko, Yong Nam Kwon, Jung Hwan Lee, Dong Hyuk Shin, Chong Soo Lee
Abstract: Cavitation behavior during superplastic flow of ultra-fine grained (UFG) Ti-6Al-4V alloy was established with the variation of grain size and misorientation. After imposing an effective strainup to 8 via equal-channel angular pressing (ECAP) at 873 K, alpha-phase grains were markedly refined from 11 μm to ≈ 0.3 μm, and misorientation angle was increased. Uniaxial-tension tests were conducted for initial coarse grained (CG) and two UFG alloys (ε = 4 and 8) at temperature of 973 K and strain rate of 10-4 s-1. Quantitative measurements of cavitation evidenced that both the average size and the area fraction of cavities significantly decreased with decreasing grain size and/or increasing misorientation. It was also found that, when compared to CG alloy, cavitation as well as diffused necking was less prevalent in UFG alloys, which was presumably due to the higher value of strain-rate sensitivity. Based on the several theoretical models describing the cavity growth behavior, the cavity growth mechanism in UFG alloys was suggested.
Authors: In Jun Hwang, Kang Min Lee, Bong Young Yoo, Dong Hyuk Shin
Abstract: Characterization of nickel oxide layers on the AZ91 Mg alloys by plasma electrolytic oxidation (PEO) was investigated. For this purpose, PEO coating was carried out on the present sample in the alkaline electrolyte with nickel ion at three different voltage responses, i.e., 150, 250, 350 V. The amount of nickel oxide increased by increasing process time, and changed the color of sample from light grey to moderate olive brown. It was observed from potentio-dynamic polarization analysis that polarization resistance of oxide layer was increased with increasing nickel ions. Also microhardness of the sample processed at 350 V was higher than those of the samples.
Authors: Bong Kwon Chung, Young Gun Ko, Kang Min Lee, Dong Hyuk Shin
Authors: Y.G. Ko, Y.G. Kim, S. Namgung, Dong Hyuk Shin, Sung Hak Lee
Abstract: In this study, dynamic deformation behavior of submicrocrystalline aluminum alloy was established with respect to equal-channel angular (ECA) pressing routes such as A, B, and C. After 8-pass ECA pressings, the deformed samples, regardless of the routes applied, were consisted of ultrafine grains together with high dislocation density near the boundaries. Microstructural observation revealed that the sample deformed via route B showed more diffused diffraction pattern than those deformed via route A and C, suggesting the fact that route B was most effective for a rapid evolution in the grain boundary orientation from low-angle to high-angle characteristics. In the torsion tests, the shear stress decreased once reaching the maximum point. This maximum was the highest in the sample deformed via route B, and decreased in the order of the route C and route A. The dynamic deformation was explained based on microstructural uniformity associated with ECA pressing routes.
Authors: Si Young Chang, Ki Seung Lee, Seong Hee Lee, Sung Kil Hong, Kyung Tae Park, Dong Hyuk Shin
Authors: Yong Suk Kim, Suk Ha Kang, Dong Hyuk Shin
Abstract: The cross-ARB (C-ARB) process, which adopts cross rolling of the two stacked plates, has been performed up to seven cycles on a commercial purity 1050 aluminum alloy to obtain ultrafine grains with an average grain size of 0.7μm. Microstructural evolution of the C-ARB processed aluminum alloy was examined by a transmission electron microscopy as a function of process cycle number (accumulated plastic strain). Tensile property of the severely deformed Al alloy was also explored. Grain size of grains of the C-ARB processed alloy varied across thickness of the rolled plate. The size of grains at the top and bottom of the rolled plate converged to 0.65μm, while that of grains at the center of the plate increased with the number of ARB cycles. Tensile strength of the CARB processed 1050 Al alloy increased from 100MPa (as-received) to 160MPa. Tensile elongation varied with the number of cycles, but 15% of failure strain was measured from the 6-cycle C-ARB processed specimen. The variation of the elongation with the cycle number coincided exactly with the variation of grain size at the center of the processed plate.
Authors: W.H. Kim, H.H. Cho, J.H. Cha, S.I. Kwun, Dong Hyuk Shin
Abstract: The effects of equal channel angular pressing (ECAP) and subsequent heat treatment on the low cycle fatigue properties of 6005 Al alloy were investigated. The ECAPed specimens showed cyclic softening, whereas the peak aged specimens showed cyclic hardening at all strain amplitudes. After ECAP, artificial aging was performed at 175°C to observe the change of the low cycle fatigue properties due to precipitation. The fatigue life and behavior of the unECAPed and ECAPed 6005 Al alloys were discussed in terms of the microstructural changes and aging conditions.
Authors: Young Gun Ko, Y.H. Lee, Won Seok Jung, Dong Hyuk Shin, Chong Soo Lee
Authors: Seng Ho Yu, Dong Hyuk Shin, No Jin Park, Moo Young Huh, Sun Keun Hwang
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