Si Young Sung

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.

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.

Titanium Alloys Casting for Structural Application

The aim of this study is to clarify the metal-mold reaction for the economic net-shape forming of titanium and titanium alloys. The metal-mold reactions between pure titanium, TiAl alloys and Al2O3 mold were examined in a plasma arc melting furnace. The alpha-case generation between pure titanium 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, based on the interstitial and substitutional α-case formation mechanism, the α-case formation between pure titanium and Al2O3 mold, and α-case free casting of TiAl alloys against Al2O3 mold can be explained. On the basis of the interstitial and substitutional α-case formation mechanism, α-case controlled net-shape forming of titanium and TiAl alloys can be possible for the structural materials.

In Situ Synthesis of TiAl Matrix Composites by Melting Route

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.

Evaluation of Interfacial Reaction between Titanium Matrix Composites and Aluminium Alloy

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.

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.

Casting and Modeling of Titanium Matrix Composites

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.

Thermodynamic Calculation of Alpha-Case Formation in Titanium Alloys

The alpha-case formation mechanism was elucidated for the economic titanium casting. The α-case formation reaction between Ti and Al2O3 mold was examined in a plasma arc melting furnace. The reaction products were characterized by electron probe micro-analyzer and transmission electron microscopy. The α-case generation between Ti and Al2O3 mold was not able to 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, from our experimental results and thermodynamic calculations and Calphad modeling (Thermo-calc®), it was confirmed that the α-case is formed not only by an interstitial element but also by substitutional metallic elements dissolved from mold materials. Our newly established α-case formation mechanism will surely lead to a variety of significant applications of the α-case controlled Ti casting.

Interfacial Reaction between Molten Al Alloys and Titanium Matrix Composites

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.