• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1934-1937
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• 1999

A copper-tungsten sintered alloy(Cu-W) has been friction-welded to a tough pitch copper (Cu) in order to investigate friction weldability. The tensile strength of the friction welded joint was increased up to 87% of the Cu base metal under the condition of friction time 1.0 see, friction pressure 40MPa and upset pressure 100MPa, upset time 5.0 sec. And it is related to upset pressure rather than friction time. Mixed layer was formed in the Cu adjacent weld interface and W particles which were included in mixed layer could induce fracture in the Cu adjacent to the weld interface. Thickness of mixed layer was reduced as upset pressure increase.

• Journal of Powder Materials
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• v.6 no.4
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• pp.320-324
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• 1999

The formation, microstructure and properties of novel ceramic composite materials manufactured by active-filler-controlled polymer pyrolysis were investigated. In the presence of active filler particles such as transition metals, bulk components of various geometry could be fabricated from siliconorganic polymer. Molybdenum- and tungsten-filled polymer suspensions were prepared and their conversion to ceramic composites by annealing in $CH_4$ atmosphere were studied. Dimensional change. porosity and phase distribution (filler network) were analyzed and correlated to the resulting hardness values. Molybdenum and tungsten as active filler were carburized completely to $Mo_2C$, $W_2C$ and WC in $CH_4$ atmosphere. Consequently, microcrystalline composites with the filler reaction products embedded in a silicon oxycarbide glass matrix were formed. Hardness was increased with increasing carburization and reached 8.6-9.5 GPa in the specimen pyrolyzed in $CH_4$ atmosphere.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1157-1158
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• 2006

Internally nitrided dilute W-Ti alloy specimens having a heavily deformed surface microstructure were prepared by a multi-step internal nitriding at 1573-2073 K. Primary nitriding below their recrystallization temperature induced a precipitation of ultrafine TiN particles. After secondary and tertiary nitriding, those precipitates grew into rod-like TiN with a length of 20-60 nm. The recrystallization temperature after nitriding was elevated above 2073 K. The yield strength at 1773 K obtained from nitrided W-0.5 mass% Ti alloy was about 5 times as large as that of the recrystallized specimen. DBTT of the nitrided alloys was about 373 K.

• Journal of Powder Materials
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• v.11 no.2
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• pp.130-136
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• 2004

The passivation and oxidation process of tungsten and molybdenum narlopowders, produced by electrical explosion of wires was studied by means of FE-SEM, XPS. XRD, TEM, DIA-TGA and sire distribution analysis. In addition, the phase transformation of W and Mo nanopowders under oxidation in air was investigated. A chemical process is suggested for the oxidation of W and Mo nano-particles after a comprehensive testing of passivated and oxidized powders.

• Journal of Plant Biology
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• v.37 no.1
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• pp.27-36
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• 1994

For establishing a transformation system of rice, an efficient introduction of foreign genes into embryogenic cell suspension by particle bombardment was conducted. The particle inflow gun based on the acceleration of DNA-coated tungsten particles using pressurized helium was constructed for delivery of DNA into rice cells. Several bombardment parameters were optimized using the transient expression of GUS gene. The conditions that gave the highest GUS gene expression of about 1000 blue spots per g fresh weight of bombarded cells include treatment of the cells with 0.5 M osmotic pressure, and use of the 410 kPa helium, 110 mm target distance, 13 mm syringe filter holder and 5 $\mu$L DNA/tungsten mixtures. It was also confirmed that rice actin promoter-intron construct gave the highest expression of all promoter-sequences studied. Eight weeks after the bombardment, stably transformed calluses were obtained on the selection medium containing 100 mg/L G418 and showed the strong activity in in situ GUS assay.

• Journal of the Korean institute of surface engineering
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• v.23 no.2
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• pp.11-17
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• 1990

The erosion characteristice of plasma-sprayed tungsten carbide chromium carbide coatings were investigated. Erosion tests were perfomed at room temperature by using Al2O3 and SiC particles accleerated in air stream. Weight losses of the coatings were measured over a range of paricle velocities and impingement angle. It was found that, for both of this coatings, the maximum erosion occurrd at a normal angle of impact, and the erosion rate at this impact angle was a power function of pparticle velocity. The values of the velocty emponent were between 3.07 and 3.50 Erosion value of chromium carbide coating was higher than that of tungsten carbide coating.

• Nuclear Engineering and Technology
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• v.54 no.3
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• pp.975-983
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• 2022

A four-layered W/Cu functionally graded material (FGM) (W90% + Cu10%/W80% + Cu20%/W70% + Cu30%/W60% + Cu40%, wt.% fraction) and a four-layered diamond/W-Cu FGM (W90% + Cu10%/W80% + Cu20%/W70% + Cu30%/W55% + Cu40% + diamond5%, wt.% fraction) were fabricated by microwave sintering. The thermal conductivity and thermal shock resistance of diamond/W-Cu FGM and W-Cu FGM were investigated. The morphologies of the diamond particles and different FGMs were analyzed using AFM, SEM, EDS, and TEM. The results show that a 200 nm rough tungsten coating was formed on the surface of the diamond. The density of the tungsten-coated diamond/W-Cu FGM, obtained by microwave sintering at 1200 ℃ for 30 min, was 94.66%. The thermal conductivity of the fourlayered diamond/W-Cu FGM was 220 W·m^-1·K^-1, which is higher than that of the four-layered W/Cu FGM (209 W m^-1 K^-1). This indicates that adding an appropriate amount of tungsten-coated diamond to the high Cu layer W/Cu FGM improves the thermal conductivity of the composite. The diamond/W-Cu FGM sintered at 1200 ℃ for 10 min exhibited better thermal shock resistance than diamond/W-Cu FGM sintered at 1100 ℃ for 10 min.

• Journal of Mechanical Science and Technology
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• v.18 no.5
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• pp.770-779
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• 2004

This paper describes the micro cutting of wear resistant tungsten carbides using PCD (Poly-Crystalline Diamond) cutting tools in performance with SEM (Scanning Electron Microscope) direct observation method. Turning experiments were also carried out on this alloy (V50) using a PCD cutting tool. One of the purposes of this study is to describe clearly the cutting mechanism of tungsten carbides and the behavior of WC particles in the deformation zone in orthogonal micro cutting. Other purposes are to achieve a systematic understanding of machining characteristics and the effects of machining parameters on cutting force, machined surface and tool wear rates by the outer turning of this alloy carried out using the PCD cutting tool during these various cutting conditions. A summary of the results are as follows: (1) From the SEM direct observation in cutting the tungsten carbide, WC particles are broken and come into contact with the tool edge directly. This causes tool wear in which portions scrape the tool in a strong manner. (2) There are two chip formation types. One is where the shear angle is comparatively small and the crack of the shear plane becomes wide. The other is a type where the shear angle is above 45 degrees and the crack of the shear plane does not widen. These differences are caused by the stress condition which gives rise to the friction at the shear plane. (3) The thrust cutting forces tend to increase more rapidly than the principal forces, as the depth of cut and the cutting speed are increased preferably in the orthogonal micro cutting. (4) The tool wear on the flank face was larger than that on the rake face in the orthogonal micro cutting. (5) Three components of cutting force in the conventional turning experiments were different in balance from ordinary cutting such as the cutting of steel or cast iron. Those expressed a large value of thrust force, principal force, and feed force. (6) From the viewpoint of high efficient cutting found within this research, a proper cutting speed was 15 m/min and a proper feed rate was 0.1 mm/rev. In this case, it was found that the tool life of a PCD tool was limited to a distance of approximately 230 m. (7) When the depth of cut was 0.1 mm, there was no influence of the feed rate on the feed force. The feed force tended to decrease, as the cutting distance was long, because the tool was worn and the tool edge retreated. (8) The main tool wear of a PCD tool in this research was due to the flank wear within the maximum value of $V_{max}$ being about 260 $\mu\textrm{m}$.

• Journal of Powder Materials
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• v.9 no.4
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• pp.273-279
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• 2002

In this study, the WC-10 wt.%Co nanopowders doped by grain growth inhibiter were produced by three different methods based on the spray conversion process. Agglomerated powders with homeogenous distribution of alloying elements and with internal particles of about 100-200 nm in diameter were synthesized. The microstructural changes and sintering behavior of hardmetal compacts were compared with doping method and sintering conditions. The microstructure of hardmetals was very sensitive to doping methods of inhibitor. Nanostructured WC-Co hardmetal powder compacts containing TaC/VC doped by chemical method instead of ball-milling shown superior sintering densification, and the microstructure maintained ultrafine scale with rounded WC particles.

• Korean Journal of Materials Research
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• v.27 no.10
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• pp.513-517
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• 2017

An optimum route to fabricate a hybrid-structured W powder composed of nano and micro size powders was investigated. The mixture of nano and micro W powders was prepared by a ball milling and hydrogen reduction process for $WO_3$ and W powders. Microstructural observation for the ball-milled powder mixtures revealed that the nano-sized $WO_3$ particles were homogeneously distributed on the surface of large W powders. The reduction behavior of $WO_3$ powder was analyzed by a temperature programmed reduction method with different heating rates in Ar-10% $H_2$ atmosphere. The activation energies for the reduction of $WO_3$, estimated by the slope of the Kissinger plot from the amount of reaction peak shift with heating rates, were measured as 117.4 kJ/mol and 94.6 kJ/mol depending on reduction steps from $WO_3$ to $WO_2$ and from $WO_2$ to W, respectively. SEM and XRD analysis for the hydrogen-reduced powder mixture showed that the nano-sized W particles were well distributed on the surface of the micro-sized W powders.