Myoung Gyun Kim

Synthesis of In-Situ Titanium Carbide Particle Reinforced Titanium Composites

Titanium carbide particle reinforced titanium composites were prepared by in-situ synthesis reaction between titanium and carbon liquid alloys. The phases constitute and microstructures of titanium composite have been investigated by OM, XRD, SEM and EPMA. Although it was possible to synthesize titanium carbide particle reinforced titanium composites, the morphology of in-situ titanium carbide grows into typically dendritic shape due to the compositional supercooling theory. Using computerized image analysis, the average particle size and aspect ratio of in-situ formed titanium carbide is about 28.1 ㎛ and 1.9, respectively.

Iron Removal in Aluminum Melts Containing Scrap by Electromagnetic Stirring

Excessive iron in aluminum melt produces needle-shaped beta-AlFeSi intermetallic compounds during solidification. The presence of beta-AlFeSi intermetallic compounds can be harmful in the extrusion process because of the high pressure. As a common process, those compounds change from the needle-shaped to the globular-shaped alpha-AlFeMnSi intermetallic compounds through the addition of manganese to the aluminum melt. Those phases settle down during the solidification process, and then such is cut. Note, however, that the efficiency of iron elimination is very low. Our previous study reported that EMS can help the alpha-AlFeMnSi intermetallic compounds form easier and faster and settle down at the bottom of the aluminum melt through the centrifugal force of EMS. To investigate the effect on the efficiency of iron elimination in aluminum melt scrap, EMS current, holding temperature, and time of melt as well as the ratio of manganese to iron were controlled. As a result of this study, lower holding temperature and longer holding time of aluminum melt make iron elimination in aluminum melt more efficient with induced EMS. The best efficiency of iron elimination in aluminum melt was 65.2%with EMS induced at 923k for 4 minutes.

Continuous Casting and Rolling for Aluminum Alloy Wire and Rod

Since the Continuous Casting & Rolling of the non-ferrous metal by Illario Properzi have invented in 1944, the various non-ferrous rod, wire and sheet are produced at present. Although there is long research and trials for producing the wire or rod of commercial the high-strength aluminum alloy, there are few companies with the success in producing commercial hard-aluminum alloys wire and rod by CC&R process. The application of the high-strength aluminum alloy rod or wire is various parts such as rivet, bolt, sports leisure supplies, high-tension power transmission wire, machinable and forgeable materials. However, it is very difficult to produce the high-strength aluminum alloy wire and rod by CC&R process because of the wide mushy zone and high strength compared with the pure or low strength aluminum alloy. Additionally, it is easy to crack and breakout in casting and rolling process due to tiny internal defects of the castings. The object of this project is to design the most suitable equipments for CC&R and optimize the experimental condition of continuous casting condition of the high-strength aluminum alloy. The facilities of CC&R process in RIST are composed of the melting furnace, the wheel casting machine, the automatic machine for moving of castings bar, the 15-step rolling machine with three rolls, the induction heater for reheating the castings bar and the coiling machine. In the present work, through the numerical computer simulation, in first, we have developed the thermal model of the solidification behavior of the casting bar. Finally, using finite element code, Marc, the temperature distribution of each rolled bar and effective strain are obtained during continuous rolling.

Investment Casting of Near-Net Shape Gamma Titanium Aluminide Automotive Turbocharger Rotor

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.

Investment Casting of Titanium Matrix Composites

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.

Continuous Casting of Magnesium Alloy Billet Using Electromagnetic Techniques

Currently, magnesium billets produced by ingot casting or direct chill casting process, result in low-quality surfaces and peer productivity. Continuous casting technology for high-quality surface billets with fine-grained and homogeneous microstructure can be a solution for the cost barrier breakthrough. The latent heat of fusion per weight (J/g) of magnesium is similar to that of other metals, however, considering the heat emitted to the mould surface during continuous casting in meniscus region and converting it to the latent heat of fusion per volume, magnesium will be rapidly solidified in the mould during continuous casting, which induces subsequent surface defect formation. In this study, electromagnetic casting and stirring (EMC and EMS) techniques are proposed to control solidification process conveniently by compensating the low latent heat of solidification by volume and to fabricate magnesium billets with a high quality surface.

Electromagnetic Continuous Casting Process for Near Net Shape Aluminum Alloy Billet

A new method and apparatus for the fabrication of high-quality, near net shaped aluminum alloy billets is developed by the combination of continuous casting and electromagnetic casting/stirring technique. Traditional machine for continuous casting process involves round, square and rectangular billets; therefore it requires additional multistep forging process to fabricate final products of complicated shape. A new process for the fabrication of near net shaped aluminum billets offers some advantages: the process of extrusion and forging is simplified and the cost of plastic working can be greatly reduced. In order to reduce the peculiar problems such as surface crack and internal defect due to inhomogeneous heat transfer of solidified billets, electromagnetic casting and stirring technique were adopted. The effect of electromagnetic field was compared by observing the microstructure of billets. Grain refinement of aluminum billet was clearly observed by applying electromagnetic field to continuous casting process.

Titanium Carbide Particulate Reinforced Titanium Based Composite by In Situ Process

Titanium carbide particle reinforced titanium composites were prepared by in-situ synthesis reaction between titanium and carbon liquid alloys. The phases constitute and microstructures of titanium composite have been investigated by OM, XRD, SEM, EPMA and TEM. Although it was possible to synthesize titanium carbide particle reinforced titanium composites, the morphology of in-situ titanium carbide grows into typically dendritic shape due to the compositional supercooling theory. The observation of TEM also show that interfaces between the reinforcements and the titanium matrix alloy are very clean.

Titanium and Titanium Alloy Castings for Biomedical Application

The aim of this study is to optimize the economic net-shape forming of titanium and titanium alloys for the biomedical application. The alpha-case formation reaction between titanium, and Al2O3, ZrO2, CaO stabilized ZrO2 and ZrSiO4 mold were examined in a plasma arc melting furnace. Regardless of the thermodynamic approach, α-case formation reactions still remain to be eliminated with the complex chemical milling processes. The reason why the α-case generated cannot be explained by the conventional α-case formation mechanism. However, from the experimental results and thermodynamic consideration, it can be 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 interstitial and substitutional α-case formation mechanism, α-case controlled net-shape forming of titanium and titanium alloys can be possible for the biomedical application.