• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.2
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• pp.102-111
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• 1997

This paper deals with the machinability based on turning of WC-Co allows with the coated and the sintered diamond tools. The main conclusions obtained are as follows. (1) When machining WC-10%Co alloy, the flank wear of sintered diamond tool increases more largely with the increase of cutting speed in comparison with coated diamond tool. The tool wear decreases with the increase of the grain size and nose radius of sintered diamond tool. (2) When machining WC-20%Co alloy, the tool wear and cutting force decrease with the decrease of rake angle. Their exists a certain cutting speed range to exhibit the smallest tool wear in machining the WC-20%Co alloy, and this critical cutting speed becomes higher by 2 times in the case of coated diamond tool compared with sintered diamond tool. (3) The machinability becomes better with the increase of Co content. The effects of cutting speed and feed rate on the roughness of machined surface become smaller with the increase of Co content.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1330-1332
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• 1998

Polycrystalline diamond films are deposited on a Si substrate by employing a 2.45 GHz $\mu$-wave plasma CVD system. Prior to depositing the diamond film, a DPR(diamond photo-resist) layer is coated to enhance the nucleation density. The growth rate of diamond films increases with the $\mu$-wave power and approaches to be about $1.5{\mu}m/hr$ at 1100 W. Structural properties of diamond films deposited are characterized from their SEM photographs, Raman spectra, and AFM surface images. Lager grain size, higher intensity of diamond peak, and smoother surface are observed for films deposited at a higher power. The possible mechanism on the diamond growth is also discussed to explain the experimental results.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1533-1536
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• 2001

To grow the diamond films by using RF-MW two step process, at first, diamond seeds were deposited on silicon substrate by RF plasma CVD, and then a diamond layer grown by MW plasma CVD on the seeds. The grain-size of diamond films deposited by using RF-MW two step process was smaller and denser and also, crystallity of diamond film was better than those of the MW plasma CVD process. The deposited diamond films were analyzed by SEM(scanning electron microscophy), XRD (x-ray diffraction), and Raman spectroscopy.

• Journal of the Korean institute of surface engineering
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• v.29 no.5
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• pp.540-544
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• 1996

To apply the CVD diamond film to coated tools, it is necessary to make adhesion strength between diamond film and substrate stronger. So adhesion strength of diamond coated WC-Co tools using Microwave Plasma CVD and cutting test of Al-18mass%Si alloy using diamond cutting tools were studied. Diamond coating was carried out using Microwave Plasma CVD apparatus. Reaction gas was used mixture of methane and hydrogen. Substrate temperature were varied from 673K to 1173K by control of microwave output power and reaction pressure. By observation of SEM, grain size became larger and larger as substrate temperature became higher and higher. Also all deposits were covered with clear diamond crystals. XRD results, the deposits were identified to cubic diamond. An analysis using Raman spectroscopy, the deposit synthesized at lower substrate temperature (673K) showed higher quality than deposit synthesized at higher substrate temperature (1173K). As a result of scratch adhesion strength test, from 873K to 1173K adhesion strength decreased by rising of substrate temperature. The deposit synthesized at 873K showed best adhesion strength. In the cutting test of Al-18mass%Si alloy using diamond coated tools and the surface machinability of Al-Si works turned with diamond coating tools which synthesized at 873K presented uniform roughness. Cutting performance of Al-18mass%Si alloys using diamond coated WC-Co tools related to the adhesion strength.

• 한국정보디스플레이학회:학술대회논문집
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• 2000.01a
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• pp.135-136
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• 2000

Field emission mechanism of undoped polycrystalline diamond films with a different amount of nondiamond carbon has been investigated using a transparent anode imaging technique and an electrolytic decoration technique. It is confirmed that for the films with a large amount of nondiamond carbon, electron transport occurs mainly through conductive grain boundaries while for the films with a small amount of nondiamond carbon, electron transports preferentially through diamond surface.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.2
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• pp.100-107
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• 1998

Diamond wheels with fine grains and multi-porous structures are newely trial developed for smoothing and mirror finishing materials. Grinding wheel must have performed both to remove tool marks efficienitly and to contact elastically with curved surfaces, that are employed for ultra precision and high performance grinding of difficult-to materials such as tungsten carbide alloy using tool and die materials, Diamond grains are bonded by a melamine resin to prevent the decrease of machining efficiency due to grain sinking within the bond materials. Also, highly foamed structures are developed to increase the flexibility of the grinding wheel, and to induce self-sharpening by increasing contact pressure between the grinding wheel and workpiece surfaces. In this paper, melamine-bonded diamond wheels try to manufacture, then the forming method of grinding wheel are suggested, and the grinding characteristics of melamine-bonded diamond grinding wheel are also illustrated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.317-326
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• 2004

This study investigated tile local austenite grain size (AGS) distribution In rolling of SCM435 steel which is commonly used for high strength bolt. To investigate AGS distribution, round-oval (R-O) and square-diamond (S-D) rolling experiments were carried out with pilot mill. In round-oval rolling, local AGS has a tendency to increase when it goes to outward. In square-diamond rolling, local AGS has a tendency to increase when it goes to free surface. To investigate relation between AGS and process parameter, three dimensional FE analysis was carried out along with rolling experiment. To validate accuracy of FE analysis, we compared deformed geometry with FE result. The AGS prediction combined AGS model with numerical analysis was also carried out for center node of S-D rolling. Although this study brought experimental observation and its qualitative analysis into focus and quantitative AGS prediction will be done as a further work.

• Journal of the Korean Ceramic Society
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• v.41 no.10 s.269
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• pp.728-734
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• 2004

The effect of microstructure of WC-Co substrates which have different WC grain sizes from submicron to 5 $\mu$m on the diamond-substrate adhesion strength was investigated. The substrates were pre-treated by two methods : chemical etching with Murakami's solution and subsequently with $H_2SO_4$, and thermal heat-treatment. The adhesion strength was estimated by degree of peeling after Rockwell indentation. Diamond films of 20 $\mu$m thickness deposited on the heat-treated substrates showed an excellent adhesion strength at the load of 100 kg, which ascribed to the large and elongated WC grains. However, the cutting edge of insert was deformed after heat treatment and the surface morphology of heat treated substrate strongly affected on the surface roughness of the deposited diamond films. On the contrary, the diamond film of 10 $\mu$m in thickness on the chemically etched substrates of average WC grain size over 2 $\mu$m showed good adhesion strength enough not to peel-off under a load of 60 kg. Especially, the substrate of average WC grain size over 5 $\mu$m exhibited much improved reliability of adhesion comparing with the substrate of average grain size under 2 $\mu$m. No substrate deformation was observed in this case after the chemical etching, which is more advantageous and more practical in terms of precious machining than the heat treatment case.

• Korean Journal of Materials Research
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• v.10 no.9
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• pp.593-600
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• 2000

This paper investigated the conduction path and conduction mechanism in undoped polycrystalline diamond thin films deposited by microwave chemical vapor deposition. The resistances measured by ac impedance spectroscopy with different directions can not be explained by the previously-known surface conduction model. The electrodeposition of Cu and electroetching of Ag experiments showed that the conduction path is the grain boundaries within the diamond films. The electodeposition of Cu with an insulating surface layer further proved that the main conduction path in polycrystalline films in the grain boundaries. The film with high electrical conductivity has low activation energy of 45meV and higher dangling bond density. By considering the results and surface C chemical bonds, the H-C-C-H bonds at surface and in grain boundaries might be the origin of high conductivity in undoped diamond films.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.12
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• pp.2172-2178
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• 1997

Development of diamond wheel with fine grains and multi-pore structures were newely attempted. Wheels, that are employed for ultra precision and high performance grinding of difficult-to materials such as tungsten carbide alloy using tool and die materials, must have both performances to remove tool marks efficiently and to contact elastically with curved surfaces. Diamond grains were bonded firmly by a melamine resin to prevent the decrease of machining efficiency due to grain sinking within the bond materials. Also, highly foamed structures were developed to increase the flexibility of the wheel, and to induce active self-sharpening by increasing contact pressure between the wheel and work surfaces. In this paper, melamine-bonded diamond wheels are trial manufactured, then the forming method of wheels are suggested, and the grinding characteristics of wheels are also illustrated.