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S.Y. Chang, H.S. Jang, Y.H. Yoon, Y.H. Kim, J.Y. Kim, Y.K. Lee and W.H. Lee

Abstract

Electrical discharges using a capacitance of 450 μF at 0.5, 1.0, and 1.5 kJ input energies were applied in a N2 atmosphere to obtain the mechanical alloyed Ti3Al powder without applying any external pressure. A solid bulk of nanostructured Ti3Al was obtained as short as 160 μsec by the Electrical discharge. At the same time, the surface has been modified into the form of Ti and Al nitrides due to the diffusion process of nitrogen to the surface. The input energy was found to be the most important parameter to affect the formation of a solid core and surface chemistry of the compact.

Open access

S.Y. Chang, Y.W. Cheon, Y.H. Yoon, Y.H. Kim, J.Y. Kim, Y.K. Lee and W.H. Lee

Abstract

Characteristics of electro-discharge-sintering of the Ti-37.5at.% Si powder mixture was investigated as a function of the input energy, capacitance, and discharge time without applying any external pressure. A solid bulk of Ti5Si3 was obtained only after in less than 129 μsec by the EDS process. During a discharge, the heat is generated to liquefy and alloy the particles, and which enhances the pinch pressure can condensate them without allowing a formation of pores. Three step processes for the self-consolidation mechanism during EDS are proposed; (a) a physical breakdown of oxide film on elemental as-received powder particles, (b) alloying and densifying the consolidation of powder particles by the pinch pressure, and (c) diffusion of impurities into the consolidated surface.

Open access

W.H. Lee, C.S. Hong and S.Y. Chang

Abstract

The initial ferrite powders were subjected to high energy ball milling at 300rpm for 3h, and subsequently heat-treated at 573-1273K for 1h. Based on the observation of microstructure and measurement of magnetic properties, the heat-treatment effect was investigated. The size of initial powders was approximately 70μm. After milling, the powders with approximately 230nm in size were obtained, which were composed of the nano-sized particles of approximately 15nm in size. The milled powders became larger to approximately 550nm after heat-treatment at 973K. In addition, the size of particles increased to approximately 120nm with increasing temperature up to 973K. The coercivity of initial powders was almost unchanged after milling, whereas the saturation magnetization increased. As the heat-treatment temperature increased, the saturation magnetization gradually increased and the maximum coercivity was obtained at 773K.

Open access

H.-Y. Gil, E. H. Lee, I.-Y. Choi, M. S. Roh and C. S. Chang

Abstract

Pinus parviflora Siebold et Zucc. on Ulleung Island, Korea, has been proposed to be more closely related to P. armandii Franch. because both have long leaves and seeds that are either wingless or have very short wings. Randomly amplified polymorphic DNA (RAPD) markers using nine primers and sequence analysis of the trnG gene and the matK gene and morphological characteristics of seeds and cones were used to assess the genetic relatedness of this taxon on Ulleung Island with P. armandii in China and P. parviflora in Japan. This current study showed that Pinus armandii from China, P. parviflora from Japan, and P. parviflora populations of Ulleung Island formed distinct groups that were separated from each other. P. parviflora from Ulleung Island grouped with P. parviflora from Japan, rather than P. armandii from China based on the RAPD dendrogram and SNPs in matK. It is believed that P. parviflora on Ulleung Island is genetically well differentiated, indicating limited gene flow from Japan, although cones and seeds of P. parviflora on Ulleung Island are more similar to var. parviflora in southern Japan than P. armandii in central China. It seems that the entities that comprise P. parviflora exhibit widely overlapping ranges in morphological attributes except leaf length.

Open access

W.H. Lee, Y.H. Yoon, Y.H. Kim, Y.K. Lee, J.Y. Kim and S.Y. Chang

Abstract

A single pulse of 2.0 to 3.5 kJ of input energy from a 450 mF capacitor was applied to a commercially pure Ti rod in a N2 atmosphere. The surface of the Ti rod transformed from TiO2 into titanium nitride in times as short as 159 msec, providing a bimodal morphology of the cross-section. A much higher value of hardness that was observed at the edge of the cross-section was attributed to nitrogen-induced solid-solution hardening that occurred during the electrical discharge process. The activation energy (Ea) for the diffusion process was estimated to be approximately 86.9 kJ/mol. Results show that the electrical discharge process is a possible potential method for the nitriding of Ti; advantages include a short processing time and control of the nitrided layer without dimensional changes.

Open access

W.H. Lee, Y.J. Jo, Y.H. Kim, Y.H. Jo, J.G. Seong, C.J. Van Tyne and S.Y. Chang

Abstract

Electro-Discharge-Sintering (EDS) was employed to fabricate Ti-6Al-4V porous implant prototypes from atomized powders (100 – 150 μm), that were subjected to discharges of 0.75 to 2.0 kJ/0.7g-powder from 150, 300, and 450 μF capacitors. Both fully porous and porous-surfaced Ti-6Al-4V compacts with various solid core sizes were self-consolidated in less than 86 – 155 μsec. It is known that EDS can simultaneously produce the pinch pressure to squeeze and deform powder particles and the heat to weld them together. The formation of a solid core in these prototypes depends on the amounts of both the pinch pressure and heat generated during a discharge. The size of the solid core and the thickness of the porous layer can be successfully controlled by manipulating the discharge conditions such as input energy and capacitance.

Open access

Y.J. Jo, Y.H. Yoon, Y.H. Kim, S.Y. Chang, J.Y. Kim, Y.K. Lee, C.J. Van Tyne and W.H. Lee

Abstract

A single pulse of 0.75-2.0 kJ/0.7g of atomized spherical Ti powders from 300 mF capacitor was applied to produce a microporous Ti implant compact by electro-discharge-sintering (EDS). A solid core in the middle of the compact surrounded by a microporous layer was found. X-ray photoelectron spectroscopy was employed to study the surface characteristics of the EDS Ti compact and it revealed that Ti, C and O were the main constituents on the surface with a smaller amount of N. The surface was lightly oxidized and was primarily in the form of TiO2 resulting from the air oxidation during EDS processing. The lightly oxidized surface of the EDS compact also exhibited Ti nitrides such as TiN and TiON, which revealed that the reaction between air constituents and the Ti powders even in times as short as 128 msec.