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Open access

J. Lee, Y. Noh, Y. Arai, W. Gao and C. Park

Precision Measurement of Cylinder Surface Profile on an Ultra-Precision Machine Tool

This paper describes the measurement of the surface straightness profile of a cylinder workpiece on an ultra-precision machine tool which has a T-base design with a spindle, an X-slide and a Z-slide. The movement range of the X-slide is 220 mm and that of the Z-slide is 150 mm, which have roller bearings in common. Two capacitive sensors are employed to scan a cylinder workpiece mounted on the spindle along the Z-axis. The straightness error motion of the Z-slide is measured to be approximately 100 nm by the reversal method. The straightness profile of the cylinder workpiece is evaluated to be approximately 400 nm by separation of the motion error, simultaneously.

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

Y.M. Shin and J.-H. Lee

Abstract

This study presents a simple wet-chemical process to prepare several micron-size Cu powders. Moreover, changes in powder synthesis yield and particle size are examined with different solvents, synthesis temperatures, and amounts of reducing agent during the synthesis. As a reducing agent and capping agent, L-ascorbic acid and polyvinyl pyrrolidone were used, respectively. The yields in distilled water or an ethylene glycol (EG)/distilled water mixture were higher than that in EG alone, and the yield increased with increasing temperature owing to a lower Δ Gred value. Increasing the L-ascorbic acid concentration also increased the yield. The Cu powder synthesized in 3 h at 90°C in distilled water with 272.8 mM of L-ascorbic acid showed the lowest average particle size of 2.52 μm, indicating mechanisms of short burst nucleation and reduced growth via the increased reduction rate of Cu ions. It is estimated that the nucleation step was nearly completed within 10 min in this system. The Cu powders synthesized in an ethylene glycol/distilled water mixture presented an average particle size of 3.76 μm and the highest yield of 87.9%.

Open access

J.-H. Pee, G.H. Kim, H.Y. Lee and Y.J. Kim

Abstract

Decomposition promoting factors and extraction process of tungsten carbide and tungstic acid powders in the zinc decomposition process of tungsten scraps which are composed mostly of tungsten carbide and cobalt were evaluated. Zinc volatility was suppressed by the enclosed graphite crucible and zinc volatilization pressure was produced in the reaction graphite crucible inside an electric furnace for ZDP (Zinc Decomposition Process). Decomposition reaction was done for 2hours at 650°, which 100% decomposed the tungsten scraps that were over 30 mm thick. Decomposed scraps were pulverized under 75μm and were composed of tungsten carbide and cobalt identified by the XRD (X-ray Diffraction). To produce the WC(Tungsten Carbide) powder directly from decomposed scraps, pulverized powders were reacted with hydrochloric acid to remove the cobalt binder. Also to produce the tungstic acid, pulverized powders were reacted with aqua regia to remove the cobalt binder and oxidize the tungsten carbide. Tungsten carbide and tungstic acid powders were identified by XRD and chemical composition analysis.

Open access

J.-H. Pee, G.H. Kim, H.Y. Lee and Y.J. Kim

Abstract

Typical oxidation process of tungsten scraps was modified by the rotary kiln with oxygen burner to increase the oxidation rate of tungsten scraps. Also to accelerate the solubility of solid oxidized products, the hydrothermal reflux method was adapted. By heating tungsten scraps in rotary kiln with oxygen burner at around 900° for 2hrs, the scraps was oxidized completely. Then oxidized products (WO3 and CoWO4) was fully dissolved in the solution of NaOH by hydrothermal reflux method at 150° for 2hrs. The dissolution rate of oxidized products was increased with increasing the reaction temperature and concentration of NaOH. And then CaWO4 and H2WO4 could be generated from the aqueous sodium tungstate solution. Ammonium paratungstate (APT) also could be produced from tungstic acid using by aqueous ammonium solution. The morphologies (cubic and plate types) of APT was controlled by the stirring process of purified solution of ammonium paratungstate.

Open access

J.J. Oak, Y.C. Lee and Y.H. Park

Abstract

In this study, the newly designed Al-9Si/SiC particles (SiCp) + Ti-fiber (2step-reinforced Al-9Si alloy matrix) metal matrix composites (MMCs) were fabricated by hot-pressing sintering at 560°C. 2step-reinforced Al-based MMCs were characterized by thermal shrinkage, phase transition, microstructure and tensile strength. The addition of Ti-fiber reduced thermal shrinkage was caused by temperature difference in sintering process as well as enhanced assistance for tensile strength and plastic deformation at room temperature. Experimental results reveal that the 2step-reinforcment sintering by ceramic and metal has a significant effect to increase interface bonding in boundary of each component material and the improved mechanical properties were due to the influence of interfacial product by diffusion. Tensile strength and elongation at room temperature by 2step-reinforcement were improved in 19.5% and 26.2% more than those of Al-9Si/SiCp, respectively. Especially, it reveals that diffusion direction may be varied by sintering methods at low temperature in this study.

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

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

D.-G. Lee, J. Seo, Ch. Li and Y. Lee

Abstract

Microstructural characterization and aging hardening behaviors of a new designed Ti-12.1Mo-1Fe alloy during solution treatment and aging were investigated in the present study. It is well known that when β-Ti alloys are generally under solution treatment or aging, α phases and ω phases appear or disappear dependent on heat treatment temperature and holding time. It is very necessary to understand the phase transformation phenomenon and to control the microstructure because these phases can control the drastic changes of the mechanical and physical properties of these alloys. According to the calculated [Mo]eq value and the microstructural observation, the β-transus temperature was about 780°. After the solution treatment, this alloy was composed of the β-phase and the microstructure mainly consisted of the equiaxed β grains with the average size of 25 μm. ω phases which were precipitated during aging process, played a more important role to the hardening effect than α phases. The highest hardness value of Ti-12.1Mo-1Fe alloy showed in the condition of the aging temperature of 450°. The hardening due to ω-phase precipitation can lead to a high hardness about 480 Hv but the coarse α-phase result in hardness below 300 Hv.

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.