Papers by Author: Young Jig Kim

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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.
Authors: Bong Jae Choi, Kyung Eui Hong, Jeong Il Youn, Young Jig Kim
Abstract: The main purpose of this research is to evaluate the wear resistance of titanium matrix composites (TMCs). Reinforcements, TiB and TiC, were formed by in-situ reaction between boron carbide and commercial pure titanium. The confirmation of the sound synthesis of TMCs was done by phase identification. And then, sliding wear test were carried out to verify the wear resistance of TMCs by means of the coefficient of friction, wear loss and morphology wear track. The results of wear test indicate that TMCs have superior resistance than AISI H13 tool steel at the condition of severe loads.
Authors: Won Ha, Shae K. Kim, Hyung Ho Jo, Myoung Gyun Kim, Young Jig Kim
Authors: Si Young Sung, Beom Suck Han, Young Jig Kim
Authors: Jeong Il Youn, Young Jig Kim
Abstract: This paper presents semi-solid processing of Cu-Ag alloy to produce squirrel cage for small and medium induction motors. Complete die filling could be achieved with the slug at 1065 oC, casting pressure of 9 MPa and ram speed of 0.08 m/s. There were no defects in squirrel cage and slug temperature and ram speed affected the slot filling of rotor importantly, however, casting pressure rarely has an effect of the filling in this experiment. As the same thixoforming condition, when the ram speed was 1.5 m/s, slurry could not fill the slot and solidified like a needle shape. The rapid flow like this would be the cause of non-filling defect of slot because the slurry injected and solidified in the slot firstly was became the obstacle not to flow the rest of the slurry.
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.
Authors: Shae K. Kim, Hyung Ho Jo, Gue Serb Cho, Kyong Whoan Lee, Young Jig Kim
Authors: Jin Kyu Lee, Young Ok Yoon, Hyung Ho Jo, Young Jig Kim, Shae K. Kim
Abstract: In recent year, various rheocasting methods, other than stirring in the semisolid state, have been developed to produce a fine globular primary phase in cast alloys. These new methods, called as slurry-on-demand, involve the controlled nucleation and growth/ripening of primary phase during partial solidification. In-Ladle direct thermal control (DTC) rheocasting has been competitively and successfully developed. It requires no processing equipment outside of the casting machine, no grain refinement procedure and no additional cycling time except for cooling down to the desired casting temperature. Process concept of In-Ladle DTC rheocasting is simply based on the fact that there is slurry and mush transition in the range of liquid fraction of 0.1 to 0.6 and the fact that the transition could be controlled by controlling the shape of solid and the relative energy. This study is mainly concerned about the feasibility to achieve semisolid slurry during partial solidification only through thermal and time control, this is, by In-Ladle DTC rheocasting. Based on the optimum conditions obtained by thermal modeling, microstructural evolution of Al alloys was carried out by In-Ladle DTC rheocasting. The fluidity was also investigated by In-Ladle DTC rheocasting for Al alloys.
Authors: Young Ok Yoon, Hyung Ho Jo, Hoon Cho, Shae K. Kim, Young Jig Kim
Abstract: It has been generally known that the refining efficiency in zone refining process depends on travel rate, number of pass and distribution coefficient of impurity. In the present study, the effect of distribution coefficient on copper purification was investigated by zone refining process. A numerical model capable of predicting the solute redistribution at any stage of zone refining was proposed. The composition profiles of each segment at the given condition were compared with the results of micro hardness profiles. After zone refining, metallic elements were analyzed by GDOS (Glow Discharge Optical Spectroscopy) and GDMS (Glow Discharge Mass Spectrometry). The impurities Ag, Pb, S and Ti, whose distribution coefficients are below 0.5, were concentrated at the finishing position. Cr, Mn, Si and Zn, whose distribution coefficients are between 0.5 and 1, were distributed irregularly. Fe and Ni, whose distribution coefficients are greater than 1, moved to the starting position. It was found that zone refining process was actually effective to remove impurities whose distribution coefficients are below 0.5. The experimental results agreed well with the simulation result.
Authors: Yeon Sun Choi, Won Ho Yang, Young Jig Kim, Chang Sung Seok
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