Papers by Keyword: Alpha Fe₂O₃

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: The aim of this study is to evaluated the possibility of the in-situ synthesized (TiC+TiB) reinforced titanium matrix composites (TMCs) for the application of structural materials. In-situ synthesis and casting of TMCs were carried out in a vacuum induction melting furnace with Ti and B4C. The synthesized TMCs were characterized using scanning electron microscopy, an electron probe micro-analyzer and transmission electron microscopy, and evaluated through thermodynamic calculations. The spherical TiC plus needle-like and large, many-angled facet TiB reinforced TMCs can be synthesized with Ti and B4C by a melting route.

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.

Abstract: Alpha-case formations between investment molds and TiAl alloys were investigated for economic TiAl alloys net-shape forming. The α-case reactions between mold and TiAl alloys were characterized by using optical microscopy and a hardness tester. In the case of TiAl alloys, there were no α-case formation reactions. The α-case was formed not only by interstitial oxygen elements but also by substitutional metallic elements dissolved from mold materials. There were neither interstitial nor substitutional α-case formations since TiAl alloys have both negligible solubility of oxygen and low activity in molten states. The results of the investment casting of TiAl alloys confirmed that the casting route in our study can be an effective approach for the economic net-shape forming of TiAl alloys automotive parts.

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.