The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Yeongil Jung - One of the best experts on this subject based on the ideXlab platform.
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A new in situ process in Precision Casting for mold fabrication
Journal of The European Ceramic Society, 2011Co-Authors: Eun-hee Kim, Yeongil Jung, Jae-hyun Lee, Chang-seop Lee, Ungyu PaikAbstract:Abstract A new in situ process for mold fabrication in Precision Casting has been developed to decrease processing time and production costs, and produce an environmentally friendly mold, compared with the conventional process. In the new process, the starting powder is fastened by an inorganic binder, whereas the mold in the conventional process takes its form by using an organic binder. The fixing of powders by the inorganic binder is caused by a sol–gel reaction of precursor materials. Therefore, the new mold process is more environmentally friendly and simpler than the conventional process. The inorganic binder system for the in situ process was prepared from a mixture of tetraethyl orthosilicate and poly(dimethyl siloxane) as SiO 2 precursor, and sodium methoxide as Na 2 O precursor. The prepared samples show a fracture strength of about 5 MPa, indicating that the in situ process can be applied to the fabrication of molds having high mechanical properties.
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a new binder system for preparing high strength inorganic molds in Precision Casting
Materials Chemistry and Physics, 2011Co-Authors: Yeongil JungAbstract:Abstract A new composite binder system has been developed to improve the strength and to decrease the processing time of inorganic binder mold for Precision Casting, as functions of dipping time and binder composition. The new binder system was prepared by mixing tetraethyl orthosilicate and polydimethyl siloxane as silicate precursors, and sodium methoxide as the precursor of sodium oxide. Samples of molds coated with an organic binder were dipped into the prepared binder systems, and then heat treated at 1000 °C for a period of 1 h. The fracture strength was markedly enhanced in the new binder systems owing to the increase in reaction depth, independent of the dipping time, whereas the fracture strength of the conventional binder system was not increased, even after a dipping time of 2 h. The new binder system containing 7.6 wt% PDMS showed the highest nominal strength of 8 MPa. When PDMS was used as the silicate precursor in the new binder system, the high glassification efficiency of silicate led to the higher fracture strength, resulting from the lack of hydrolysis and condensation reactions of PDMS. The fracture strength could be controlled by changing the molecular structure of binder and the binder composition.
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Development of Composite Binder System for Shell Mold in Precision Casting of Thin Stainless Steel
Materials Science Forum, 2009Co-Authors: Jae Young Kwon, Yeongil JungAbstract:New composite binder systems have been developed to improve strength of shell mold and to decrease processing time, as functions of dipping time and binder composition, which is compared with the conventional binder system. The new binder systems were prepared by mixing tetraethyl orthosilicate (TEOS) and polydimethyl siloxane (PDMS) as precursor of SiO2 and sodium methoxide (NaOMe) as precursor of NaO2. The samples of shell mold were dipped into the prepared binder systems, and then heat-treated at 1000°C for 1 hr. The fracture strength is sharply enhanced in the new binder system owing to the increase of penetration depth with the dipping time, whereas the conventional binder system is modestly increased even in the dipping time of 2 hr. The new binder system with 7.6 wt% PDMS shows the highest nominal strength, showing a nominal value of 16 GPa. When only PDMS as precursor of SiO2 was used in the new binder system, the increase of viscosity by PDMS causes a larger scattering in the strength value. The strength could be controlled with the dipping time and molecular weight, showing the lower nominal strength values at the dipping time of 0.5 hr and in the low molecular weight of TEOS/NaOMe. The relationship between strength and binder composition is discussed, based on the microstructures before and after heat-treatment.
Ken-ichiro Suzuki - One of the best experts on this subject based on the ideXlab platform.
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Stability of Yttria for Titanium Alloy Precision Casting Mold
Materials Transactions Jim, 2007Co-Authors: Ken-ichiro Suzuki, Koji Nishikawa, Siro WatakabeAbstract:Superior properties of yttrium oxide for mold material use in Precision Casting of Ti-6Al-4V alloy have been proved in experiments under simulating process conditions and by assuming a model for formation of a hardened layer in the surfaces of the castparts. The model consists of instantaneous dissociation of oxide in the mold and rapid absorption and diffusion of dissociated oxygen into Ti-6Al-4V alloy castparts during mold filling, solidification and cooling after solidification. The maximum hardness in the surface hardened layer correlates directly with the stability of oxide which depends on the activities of elements consisting of the oxide in the molten titanium alloy. The hardness profiles in the surface hardened layer are determined by diffusion of oxygen in the alloy during cooling and solidification of the castparts.
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Melting and Precision Casting of Ti-6Al-4V alloy by use of electron beam furnace
Metals and Materials International, 2003Co-Authors: Ken-ichiro Suzuki, Siro WatakabeAbstract:For melting and Casting of Ti-6Al-4V alloy by use of an electron beam furnace, key technologies have been developed: measurement and control of temperature, amount, and chemical composition of molten pool. Temperature in the molten pool was measurred by applying three devices; a thermocouple, a two color pyrometer and the rate of vaporization from the molten pool. Temperature measured by an optical pyrometer without influence of plasma by shifting the wave lengths of the light for the optical pyrometry from those of plasma evolved above the molten pool was in a good accordance with that estimated from the vaporization rate. By combining temperatures measured by three methods, the temperature gradient in the molten pool was estimated to be a level of 100 K/cm. In order to derive an empirical equation for the depth of molten pool of various metals, the depth of the molten pool was determined for Ti, Ti-6Al-4V alloy, solar grade Si, low carbon steel, and stainless steel by chemical etching of vertical cross section of an ingot melted and solidified in a skull crucible. Chemical compositions of Ti-6Al-4V alloy melt before Casting was adjusted by adding an aluminum block into the pool before pouring, which compensated vaporization loss of Al from the pool surface under high vacuum. Since, a key to settle Al content in the specified range is the yield and distribution of Al in every castparts, influences of operating variables on the yield have been studied by paying attention to rapid temperature change observed immediately after addition of aluminum.
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The high-quality Precision Casting of titanium alloys
JOM, 1998Co-Authors: Ken-ichiro SuzukiAbstract:A technique for the high-quality Precision Casting of titanium alloys has been developed that consists of the instantaneous dissociation of oxide at the metal-mold interface, followed by the rapid absorption and diffusion of the dissociated oxygen into the subsurface of the cast parts during solidification and cooling. In centrifugal Casting trials using less molten alloy than required to completely fill the mold, the results suggest that the melt flowing in the mold cavities maintains contact with the vertical inside walls and directionally solidifies from the far end of the cavity to the gate, corresponding to the gradient in the centrifugal force on the horizontal plane. This force enhances the removal of defects, such as entrapped gas bubbles and solidification shrinkage. The results have enabled the development of a two-dimensional model to simulate melt flow during centrifugal Casting.
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Mold filling and solidification during centrifugal Precision Casting of Ti-6Al-4V alloy
Materials Transactions Jim, 1996Co-Authors: Ken-ichiro Suzuki, Koji Nishikawa, Siro WatakabeAbstract:The melt flow and the mold filling process in a Precision Casting tree for Ti-6Al-4V alloy castparts have been examined by Casting trials, in which the molten alloy with an amount intentionally adjusted to be less than that required for complete filling is poured under a centrifugal force. By rotation of the tree on the horizontal plane the melt flows into mold cavities keeping contact with one of the vertical inside walls of a gate and a mold cavity. The melt in the cavity solidifies in a manner of directional solidification by accumulating solidifying layer from the far end of a cavity where the centrifugal force is maximum to a gate at which the force is minimum, namely according to the gradation of centrifugal force. The centrifugal force imposed on the melt enhances removal of gas bubbles which may evolve during the pouring of the melt into the mold cavity, reduces the number of gaseous defects to a negligibly small level at 30 G and improves the tensile strength of castparts. Dendrites are observed at the bottom of porosity where the inter-dendritic melt is sucked to the half thickness side by the solidification shrinkage. In mapping analysis of solute elements on cross sections of dendrite tips, micro segregation in a dendrite tip seems to be caused not during solidification but during transformation from the β to α phase on cooling of castparts.
Shigeki Katsura - One of the best experts on this subject based on the ideXlab platform.
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Dental Precision Casting of Ti-29Nb-13Ta-4.6Zr Using Calcia Mold
Materials Transactions, 2009Co-Authors: Harumi Tsutsumi, Mitsuo Niinomi, Toshikazu Akahori, Tsutomu Takeuchi, Masaaki Nakai, Shigeki KatsuraAbstract:The objective of this study is to develop a dental Precision Casting process for a beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy which has been developed for biomedical applications, using a mold made by electrically fused calcia particles. The effect of a combination of different sizes of calcia particles on the surface condition of the mold was investigated. In addition, to obtain a smooth surface, a cast TNTZ was made using a mold made using a mixture of calcia particles with a wax pattern conducted with calcia slurry coatings. Furthermore, surface reaction layer of the cast TNTZ was evaluated using an optical microscopy, a Vickers' hardness test and a X-ray diffractometry. The surface of the mold fabricated with a mixture of fine (diameter < 0.3 mm) and coarse (diameter = 1-3 mm) calcia particles is smooth and showed no cracks or defects. In addition, the surfaces of the cast TNTZ made using the duplex-coated wax pattern with the fine pure calcia slurry and crushed silica fiber-reinforced fine calcia slurry are very fine. Furthermore, the formation of the surface reaction layer on the cast TNTZ is remarkably inhibited. The results of this study should lead to enhancements in the creation of cast TNTZ for dental products.
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Dental Precision Casting of Ti-29Nb-13Ta-4.6Zr Using Calcia Mold
Materials Science Forum, 2005Co-Authors: Mitsuo Niinomi, Toshikazu Akahori, Tsutomu Takeuchi, Shigeki KatsuraAbstract:Duplex calcia coating method where firstly fine calcia was coated on wax pattern and then fine calcia reinforced silica fiber was coated on the fine calcia coated wax pattern, that is, duplex calcia coating method, was applied for making mold. The surface of Ti-29Nb-13Ta-4.6Zr cast using the duplex calcia coating method show very fine metallic lust. The thickness of alpha case formed on the surface of Ti-29Nb-13Ta-4.6Zr is much thinner comparing with the case where the commercial magnesia mold for Casting conventional titanium and its alloys for dental applications is used. The duplex calcia coating method is highly expected to be put into practical use for dental Precision Casting of Ti-29Nb-13Ta-4.6Zr. The dental crown of Ti-29Nb-13Ta-4.6Zr is successfully fabricated using duplex calcia coating method.
Siro Watakabe - One of the best experts on this subject based on the ideXlab platform.
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Stability of Yttria for Titanium Alloy Precision Casting Mold
Materials Transactions Jim, 2007Co-Authors: Ken-ichiro Suzuki, Koji Nishikawa, Siro WatakabeAbstract:Superior properties of yttrium oxide for mold material use in Precision Casting of Ti-6Al-4V alloy have been proved in experiments under simulating process conditions and by assuming a model for formation of a hardened layer in the surfaces of the castparts. The model consists of instantaneous dissociation of oxide in the mold and rapid absorption and diffusion of dissociated oxygen into Ti-6Al-4V alloy castparts during mold filling, solidification and cooling after solidification. The maximum hardness in the surface hardened layer correlates directly with the stability of oxide which depends on the activities of elements consisting of the oxide in the molten titanium alloy. The hardness profiles in the surface hardened layer are determined by diffusion of oxygen in the alloy during cooling and solidification of the castparts.
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Mold filling and solidification during centrifugal Precision Casting of Ti-6Al-4V alloy
Materials Transactions Jim, 1996Co-Authors: Ken-ichiro Suzuki, Koji Nishikawa, Siro WatakabeAbstract:The melt flow and the mold filling process in a Precision Casting tree for Ti-6Al-4V alloy castparts have been examined by Casting trials, in which the molten alloy with an amount intentionally adjusted to be less than that required for complete filling is poured under a centrifugal force. By rotation of the tree on the horizontal plane the melt flows into mold cavities keeping contact with one of the vertical inside walls of a gate and a mold cavity. The melt in the cavity solidifies in a manner of directional solidification by accumulating solidifying layer from the far end of a cavity where the centrifugal force is maximum to a gate at which the force is minimum, namely according to the gradation of centrifugal force. The centrifugal force imposed on the melt enhances removal of gas bubbles which may evolve during the pouring of the melt into the mold cavity, reduces the number of gaseous defects to a negligibly small level at 30 G and improves the tensile strength of castparts. Dendrites are observed at the bottom of porosity where the inter-dendritic melt is sucked to the half thickness side by the solidification shrinkage. In mapping analysis of solute elements on cross sections of dendrite tips, micro segregation in a dendrite tip seems to be caused not during solidification but during transformation from the β to α phase on cooling of castparts.
Mitsuo Niinomi - One of the best experts on this subject based on the ideXlab platform.
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Dental Precision Casting of Ti-29Nb-13Ta-4.6Zr Using Calcia Mold
Materials Transactions, 2009Co-Authors: Harumi Tsutsumi, Mitsuo Niinomi, Toshikazu Akahori, Tsutomu Takeuchi, Masaaki Nakai, Shigeki KatsuraAbstract:The objective of this study is to develop a dental Precision Casting process for a beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy which has been developed for biomedical applications, using a mold made by electrically fused calcia particles. The effect of a combination of different sizes of calcia particles on the surface condition of the mold was investigated. In addition, to obtain a smooth surface, a cast TNTZ was made using a mold made using a mixture of calcia particles with a wax pattern conducted with calcia slurry coatings. Furthermore, surface reaction layer of the cast TNTZ was evaluated using an optical microscopy, a Vickers' hardness test and a X-ray diffractometry. The surface of the mold fabricated with a mixture of fine (diameter < 0.3 mm) and coarse (diameter = 1-3 mm) calcia particles is smooth and showed no cracks or defects. In addition, the surfaces of the cast TNTZ made using the duplex-coated wax pattern with the fine pure calcia slurry and crushed silica fiber-reinforced fine calcia slurry are very fine. Furthermore, the formation of the surface reaction layer on the cast TNTZ is remarkably inhibited. The results of this study should lead to enhancements in the creation of cast TNTZ for dental products.
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Dental Precision Casting of Ti-29Nb-13Ta-4.6Zr Using Calcia Mold
Materials Science Forum, 2005Co-Authors: Mitsuo Niinomi, Toshikazu Akahori, Tsutomu Takeuchi, Shigeki KatsuraAbstract:Duplex calcia coating method where firstly fine calcia was coated on wax pattern and then fine calcia reinforced silica fiber was coated on the fine calcia coated wax pattern, that is, duplex calcia coating method, was applied for making mold. The surface of Ti-29Nb-13Ta-4.6Zr cast using the duplex calcia coating method show very fine metallic lust. The thickness of alpha case formed on the surface of Ti-29Nb-13Ta-4.6Zr is much thinner comparing with the case where the commercial magnesia mold for Casting conventional titanium and its alloys for dental applications is used. The duplex calcia coating method is highly expected to be put into practical use for dental Precision Casting of Ti-29Nb-13Ta-4.6Zr. The dental crown of Ti-29Nb-13Ta-4.6Zr is successfully fabricated using duplex calcia coating method.