Papers by Author: Jeong Whan Han

Abstract: Phase equilibrium of the Mg-Al-Sn alloy system was calculated in detail by utilizing phase diagram calculation commercial package and other thermodynamic data for Mg alloys. The calculated phase diagrams were compared with the DSC results for the alloys of Mg-3wt%Al-3wt%Sn. The solidification and precipitation process of Mg-3wt%Al-Xwt%Sn were analyzed. The detailed comparison strongly supports the reliability of the selected thermodynamic description based on the results of thermodynamic calculation. It is clarified that when the Mg-Al-Sn alloy ends its solidification and cools down continuously, the phase Mg2Sn precipitated first from solid solution of magnesium, and then the Mg17Al12 phase precipitated at relative lower temperature. This is shown that the calculation phase diagram method considerably reduces the effort of alloy design and that the reliability of the results is high.

Abstract: We present a study of the photoresist (PR) etching and the low-k materials damage using a ferrite-core inductively coupled plasma (ICP) etcher, in order to develop an etching process for the low-k dielectric devices. We reveal that the N2/O2 flow ratio and bias power affected the PR etching rate. By Fourier transform infrared spectroscopy and HF dipping test, we investigated the effect of the gas flow ratio and bias power on the amount of etching damage to the low-k material.

Abstract: Indium oxide (In2O3) films were successfully grown on LiAlO2 substrates using the triethylindium (TEI) as a precursor in the presence of oxygen in the metalorganic chemical vapor deposition process. We have established the correlation between the substrate temperature and the structural properties. The grain structures were clearly shown on the surface of the films deposited at 350°C. The root mean square (RMS) surface roughness of the In2O3 films increased with increasing the substrate temperature. A photoluminescence measurement at room temperature exhibited a yellow-green emission band centered at 585 nm.

Abstract: A cold spray process is a relatively new process using high velocity metallic particles for surface modifications. Metallic powder particles which are injected into a converging-diverging nozzle are accelerated to supersonic velocities. In this study a comparative study was performed to figure out the effect of curvature on gas and particle flow in converging-diverging nozzle. And, the critical radius of curvature in converging and diverging section of nozzle and the behavior of the gas and particle flow were determined and calculated, respectively.

Abstract: In the continuity casting technology of steel-manufacturing process, the tundish has two important functions: the preservation and distribution of molten metal and the reaction container able to perform float-out separation of nonmetallic inclusions. The residence time affects the effective removal of the nonmetallic inclusions. In this study, a T-shaped tundish with a submerged entry nozzle (SEN) and three strands was investigated for its ability to extend the residence time. Analysis conditions were the shape of the dam which was transformed to three cases. Fluid flow and non-metallic inclusion movement were also analyzed. The movement and removal of nonmetallic inclusions was determined by residence time distribution (RTD) analysis. As a result, the number of float-out, non-metallic inclusions was increased when the deviation of mean residence time was reduced.

Abstract: The cold spray process is a relatively new process using high velocity metallic particles for surface modifications. Metallic powder particles which are injected into a converging-diverging nozzle are accelerated to supersonic velocities. In this study effects of nozzle design such as diameter of nozzle throat and length of converging and diverging part of the nozzle on gas and particle velocities developed after the nozzle exit are investigated.

Abstract: From materials view point, a PCB (Printed Circuit Board) is a simple mixture of various metals, plastics and oxides. Thus, it can be regarded as urbanized resources or ores. The existence of valuable metallic components in used PCB, then, becomes a major driving force for the recycling In this study, the effect of slag compositions on the extraction of valuable metallic components from the used PCB is investigated. Especially, a melting temperature of slag and slag viscosity are discussed as major operating parameters. PCB contains nearly 30wt% of SiO2 and 20wt% of Al2O3 as major oxides, and by just adding other flux components to used PCB, 20wt%Al2O3-Xwt%SiO2 - Ywt%CaO-10wt%MgO slag system with low melting point and low slag viscosity can be made to extract metallic components from used PCB by gravity separation. The slag basicity was changed under fixed compositions of Al2O3 and MgO. It was found that a proper melting temperature and slag basicity to make a homogeneous liquid slag and to extract metallic components from used PCB were 1573 K, and 0.75, respectively.

Abstract: In the present study, we have attempted to refine a microstructure of conventional AZ31 magnesium alloy using a new combination process including hot extrusion followed by a cold equal channel angular pressing (ECAP). ECAP die was specially designed with an inner die corner angle of 135 degree, the fillet angle of 45 degree and dimensional thermo-coupled elastro-plastic material model in order to understand the change of stress and strain of the deformed material after a cold ECAP. ECAP for the AZ31 alloy, which was extruded in the extrusion ratio 20 to 1 and heat-treated at 623K, was successfully carried out at room temperature. The uniform shear band obtained from experiment was well matched with the zone of effective strain more than 0.533 estimated from calculation. On the basis of the results, it is suggested that the room temperature ECAP makes microstructure to be refined and the basal plane to be rotated slightly from extrusion direction to axis direction. Compressive yield strength of AZ31 alloy can be enhanced up to twice in applying ECAP process. Hall-Petch relations do not fit to the experimental data This can be ascribed to the texture effect. Room temperature ECAP process is very promising in improving mechanical properties of AZ31 alloy in terms of grain refinement and texture control.

Abstract: It is generally well known that a steelmaking ladle operation plays an important role in the production of clean steel. A turbulent mixing of melt with Ar gas bubbling from the ladle bottom can homogenize a melt temperature and can control precisely chemical compositions of steel. In order to figure out these phenomena, a quantitative analysis of fluid flow behavior of gas and melt during a ladle operation is required and special concerns should be focused on effects of operating parameters on the perfect mixing time of melt. In this study, as a basic approach, effects of operating parameters such as a melt depth (aspect ratio) and a nozzle type (one-hole or porous plug) on the mixing behavior in ladle operation are investigated. Water model experiments are carried out to simulate these melt behaviors in steelmaking ladle. As a result, it was found that there exist an optimized melt depth and a nozzle type at a given gas flow rate, which affect significantly on the mixing behavior of melt.

Abstract: Flow patterns and mixing behaviors in a gas stirred steelmaking ladle with a slag layer were discussed using a water model experiment as well as a numerical simulation. While the water model experiment was performed to investigate the effect of slag on the mixing behavior in ladle, the numerical simulation was carried out to figure out the flow pattern in ladle with a slag layer. Slag viscosity and its thickness in ladle were considered as major variables. It was found that a slag layer made a great change in the flow pattern in ladle, which, in turn, affected on the mixing behavior in ladle. A flow pattern without a slag layer showed that rising bubbles eventually made a recirculation loop at the central area of the ladle and this flow pattern was regarded as a favorable flow pattern for the better mixing behavior. However, a flow pattern with a slag layer showed distorted and localized recirculating loop near side wall below slag layer. This eventually gave a longer mixing time in ladle with a slag layer. Moreover, as the gas flow rate increases, slag existing on top of the ladle was found to be entrained into the melt. Slag viscosity and its thickness were found to be major variables affecting the behavior of slag entrainment. Lower the slag viscosity and thicker the slag layer, much more slag on top of the melt was entrained into the melt.