Papers by Author: Si Young Sung

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Authors: Bong Jae Choi, Si Young Sung, Young Jig Kim
Abstract: The aim of this study is to fabricate an α-case free (TiB+TiC) hybrid titanium matrix composites (TMCs) shot sleeve for aluminum alloy diecasting by in-situ synthesis and investment casting. Granular 1.88 wt% B4C was added to a titanium matrix in a vacuum induction melting furnace. The synthesized (TiB+TiC) TMCs were examined using electron probe micro-analysis and transmission electron microscopy. The results of the in-situ synthesis and investment casting of the TMCs show that our casting route constitutes an effective approach to the economic net-shape forming of TMC sleeves.
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Authors: Si Young Sung, Beom Suck Han, Young Jig Kim
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Authors: Si Young Sung, Bong Jae Choi, Young Jig Kim
Abstract: The aim of this study is to establish the net-shape forming of titanium matrix composites (TMCs) shot sleeve for Al alloys die-casting using a casting route. In-situ synthesis and casting of TMCs were carried out in a vacuum induction melting furnace. The synthesized (TiC+TiB) TMCs were examined using an scanning electron microscopy and electron probe micro-analyzer. The thermo-physical variables estimated by casting process were applied to the modeling of TMCs shot-sleeve casting using the Magmasoft®. The results of the investment casting and modeling of TMCs confirm that the casting route can be an effective approach for the economic net-shape forming of TMCs shot sleeve.
1213
Authors: Bong Jae Choi, Si Young Sung, Young Jig Kim
Abstract: The main purpose of this study is to evaluate the interfacial reaction between titanium matrix composites (TMCs) and A380 alloy in aluminum die-casting. In-situ synthesized titanium matrix composites and H13 tool steel were immersed in molten A380 alloy in a mold at 993 K for times varying from 0 to 1200 s. In-situ synthesis TMCs and interfacial reaction between TMCs and A380 alloy were examined by X-ray diffraction, optical microscope, scanning electron microscope and electron probe micro-analyzer. The reaction behavior shows that TMCs can a substitution for H13 tool steel.
433
Authors: Bong Jae Choi, Si Young Sung, Young Jig Kim
Abstract: TiAl alloys Al composition range between 45 and 49 at%, includes γ-TiAl and α2-Ti3Al, are an emerging high temperature materials which has higher specific strength, oxidation ratio and specific modulus than Ni base superalloy. In this study, TiAl alloys were manufactured by plasma arc melting (PAM) and then TiAl and granular boron carbide were in-situ synthesized in PAM method again. The in-situ synthesized TiAl matrix composites were investigated by using X-ray diffractometer, optical microscope, and electron probe micro-analyzer.
1221
Authors: Si Young Sung, Bong Jae Choi, Sang Hwa Lee
Abstract: The aim of this study is to investigate the applicability of titanium matrix composites (TMCs) sleeve to Al alloys die-casting. Ti and 1.88 mass% B4C were prepared for the synthesis of 10 vol% (TiC+TiB) hybrid TMCs. In-situ synthesis and net-shape forming of TMCs were carried out in a vacuum induction melting furnace. The synthesized (TiC+TiB) TMCs were examined using scanning electron microscopy, an electron probe micro-analyzer, X-ray diffraction and transmission electron microscopy. The resistance-ability of (TiC+TiB) TMCs to molten Al alloys attack was also examined. Their reactions were carried out in a furnace at 993 K for times varying from 0 to 1200 s. In the case of conventional sleeve material, H13 steel, there were severe interfacial reactions and erosion after 60 s. On the other hand, the resistance of (TiC+TiB) TMCs to interfacial reactions and erosion by molten A380 alloy was significantly increased.
310
Authors: Myoung Gyun Kim, Si Young Sung, Gyu Chang Lee, Joon Pyo Park, Young Jig Kim
Abstract: The objective of this study was to optimize the casting design of gamma titanium aluminde automotive turbocharger rotor by means of the practical experiment and numerical simulation. Gamma titanium aluminide rotors were produced by centrifugal casting methods on a laboratory scale. Based on the metal-mold reaction of gamma titanium aluminide, the investment molds were manufactured by an electro-fused Al2O3 mold. The experimental results showed that the castings failed to reach the end of the cavities due to insufficient centrifugal force and a lower fluidity compared to the other metals. Although the satisfactory results were not obtained in the numerical simulation, it was concluded that numerical simulation aided to achieve understanding of the casting process and defect formation in gamma titanium aluminide turbocharger rotor castings.
2547
Authors: Si Young Sung, Young Jig Kim
Abstract: The aim of this study is to clarify the alpha-case formation mechanisms for the economic net-shape forming of Ti and Ti alloys. The α-case formation reaction between Ti and Al2O3 mold was examined in a plasma arc melting furnace. The reaction products were characterized by using an electron probe micro-analyzer and transmission electron microscopy. The α-case generation between Ti and Al2O3 mold could not be explained by the conventional α-case formation mechanism, which is known to be formed by the interstitials, especially oxygen dissolved from mold materials. However, on the basis of our experimental results and thermodynamic consideration, it was confirmed that the α-case is formed not only by interstitial oxygen atoms but also by substitutional metal atoms dissolved from mold materials. Based on the α-case formation mechanism, α-case free net-shape forming of Ti and Ti alloys could be possible for biomedical applications.
794
Authors: Si Young Sung, Keun Chang Park, Myoung Gyun Kim, Young Jig Kim
Abstract: The aim of the present work is to investigate the possibility of in-situ synthesis and net-shape of the titanium matrix composites (TMCs) using a casting route. From the scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA), X-ray diffraction (XRD) and thermodynamic calculations, the spherical TiC and needle like TiB reinforced hybrid TMCs could be obtained by the conventional casting route between titanium and B4C. No melts-mold reaction could be possible between (TiC+TiB) hybrid TMCs and the SKKU mold, since the mold is composed of interstitial and substitutional reaction products. Not only the sound in-situ synthesis but also the economic net-shape of TMCs could be possible by conventional casting route.
2551
Authors: Si Young Sung, Young Jig Kim
Abstract: Over the past decades, a large number of researchers have been trying titanium alloys in an attempt to combine most of their advantages, such as high specific yield strength, good corrosion resistance, excellent fatigue property and biocompatibility by casting route. However, the wide use of titanium alloys casting has been limited, since it is considered as only a near net shape forming process in titanium alloys due to the catastrophic reactivity of molten states, the alpha-case formations and the casting defects. In order to maximize the unique property of titanium alloys casting which are comparable to wrought products and quite often superior, it is necessary to take a close examination of titanium alloys casting procedure. Therefore, the merits and demerits of various melting devices, pouring methods and mold materials will be addressed with regard to improving titanium alloys casting.
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