• Journal of Welding and Joining
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• 제21권2호
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• pp.42-49
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• 2003

The protection of steel surfaces against wear is a practical problem far agricultural, mining and manufacturing industries. Commercial processes are available in which a hard tungsten carbides rich steel layer is formed on the surface of carbon steel digging, drilling and gouging tools to improve their wear resistance. The nature of the interaction of the tungsten carbide with the steel matrix is important in determining the wear and corrosion properties of the resulting metal matrix composites(MMC). In the study, WC-12%Co/low carbon steel MMC overlays have been prepared by gas metal arc welding(GMAW) according to size of WC-12%Co grits. The characteristics wear resistance and wear mechanism have been investigated in relation to the experiment conditions each other. After MMC overlay had been tested by rubber wheel abrasion test, it was known that MMC overlay has a excellent wear resistance. Fe$_{6}$W$_{6}$C carbides of matrix in overlays were not important to restrain rubber wheal abrasion wear. Wear loss is proportioned to a applied load according to time. On the case of low load, wear occurred severely in the matrix of overlay more than WC-12%Co grit, on the contrary it is reverse on the case of high load because of fracture of WC-12%Co grits.its.

• 소성∙가공
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• 제6권5호
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• pp.446-455
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• 1997

A Combined extrusion operation consists of forward and backward extrusion forming and it is possible to make the process be simple by employing it. But the metal flow pattern induced by the operation is hard to analyze accurately because the flows are non-steady, which have at least two directions dependent upon each other. So engineers in the industrial factories had conducted the two extrusion operations separately. A new process was designed by the industrial expert for forming of an alu-minum preform using the combined extrusion operation. In this study, experiments and finite element analysis was carried out to determine the process parameters. Through the preliminary experiment, it was shown that warm forming condition was more desirable than cold or hot ones. And optimal shape of initial billet could be also determined. From the compatibility test, bonde-lube was chosen as the optimal lubricant and 20$0^{\circ}C$ as the material temperature by the inspection of micro-structure. The operation was simulated by the rigid-plastic finite element method to examine the metal flow. Disap-pearing of dead metal zone was observed as the punch fell down and desirable shape was obtained from the one operation. As a result of this study, 7 operations could be reduced and 225% of material saved.

• 한국실내디자인학회논문집
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• 제17호
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• pp.157-165
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• 1998

This study aimed to identify characteristics of design and decoration of Danish peasant furniture especially painted storage furniture used during the 18-19th century before modern design movement of Internationalism prevailed all over the world. Owing to the fact that Danish peasant furniture were made of available conifer around the farms painting method was preferred to carving. Remoted from main land of western and southern Europe Scandinavian countries longed to imitate their Baroque style architecture and furniture made of marble of hard woods. Painting method was adopted to disguise cheap wood so that it looked like expensive or exotic materials such as marble oak metal granite etc. what they could not afford to buy. Eventually they evolved unique materials equipments and methods for imitation painting in order to decorate folk storage furnitures as well as formal architecture : palaces churches and other official buildings,. Marbling clouds marbling graining stencil spatter painting trompe-I'oeil were common to imitate stones or hard woods. Strong and bright colors had good combination together with dull colors on the Danish peasant painted furniture.

• 한국재료학회지
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• 제13권6호
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• pp.394-397
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• 2003

MTJ devices are fabricated using metal shadow masks and switching characteristics are investigated under 2 dimensional magnetic field. When the hard axis field is less than $\pm$ 16 Oe, switching behavior is similar to that based on the Stoner-Wohlfarth model. As the hard axis field is larger than $\pm$ 16 Oe, deviation from the expectation by Stoner-Wohlfarth model is observed. These phenomena are induced by the generation of multi-domain and inhomogeneous magnetization reversal.

• 연구논문집
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• 통권28호
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• pp.59-71
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• 1998

The ELID(electrolytic in-process dressing) grinding method is a new precision grinding technique with the special electrolytic in-process dressing by metal bonded grinding wheel, fluid, and power supply. It is possible to make a efficient precision machining of hard and brittle materials such as ceramics, hard metals, and quenched steels by using this method, In this study, a new efficient precision grinding method with ELID was attempted for application to the machining and finishing processes of cylindrical structural components. And, we try to develop the cylindrical grinding technique for mirror surface of ceramics, tungsten carbide and SCM steel, and for the high efficiency grinding of machined parts, for example, ball screw shaft. Electrical characteristics of three different wheel grit sizes of #325, #2000 and #4000 were investigated experimentally. ELID grinding method is proved to be useful for mirror surface generation and efficient machining.

• 한국생산제조학회지
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• 제18권5호
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• pp.498-506
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• 2009

An experimental study was performed to select cutting parameters for better quality-products in hard metals such as steels. Usually, a hard metal can be cut with a rotary cutting knife and the process provides a good cutting quality result. However, the cutting machine is much sensitive in cutting conditions because of its complicated mechanism. By this reason, careful processing conditions must be taken to improve the quality of the products. This experimental study for better quality products with a rotary cutting knife was carried out with two main factors; cutting speeds and cutting and pooling forces. A two-dimensional profile measuring instrument is used to evaluate its cutting faces and the effects of processing factors are analyzed by a commercial software.

• 한국분말재료학회지
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• 제10권4호
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• pp.249-254
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• 2003

WC-6wt%Co hard metal powders were sintered by a 2.45 GHz multimode microwave applicator in Ar atmosphere. Microwave sintering of WC-6wt%Co powder lowered the sintering temperature and shortened the processing time in less than two hours than by a conventional method. Microstructures of the sintered specimen were studied with scanning electron microscope (SEM) and no abnormal grain growth was observed. Mechanical properties were similar to the values of the specimens sintered by a conventional method. Specimen sintered at 135$0^{\circ}C$ for 30 minutes ,hewed 99%, 20.5 GPa and 8.1 MPa$\sqrt{m}$ of theoretical density, hardness and fracture strength, respectively.

• 한국진공학회지
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• 제4권S2호
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• pp.163-169
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• 1995

Ion beam assisted deposition(IBAD) technique was used to synthesize hard coatings including diamond-like carbon(DLC), carbon nitride(CN) and metal-ceramic multilayered films. It was found that DLC films formed at low energy ion bombardment possess more $Sp^3$ bonds and much higher hardness. The films exhibited an excellent wear resistance. Nanometer multialyered Fe/TiC films was deposited by ion beam sputtering. The structure and properties were strongly dependent on the thickness of the individual layers and modulation wave length. It was disclosed that both hardness and toughness of the films could be enhanced by adjusting the deposition parameters. The CN films synthesized by IBAD method consisted of tiny crystallites dispersed in amorphous matrix, which were identified by electron diffraction pattern to be $\beta -C_3N_4$.

• 대한치과보철학회지
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• 제41권1호
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• pp.1-19
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• 2003

The surface of metals should be as smooth as possible for optimum comfort, oral hygiene, low plaque retention, and resistance to corrosion. In this study five specimens of each precious metal(type III gold alloy, ceramic gold alloy, and Ag-Pd alloy) were divided into five groups according to finishing and polishing procedures : group 1(sandblaster), group 2(group 1+stone), group 3(group 2+brown rubber), group 4(group 3+green rubber), and group 5(group 4+rouge). Six specimens of each non-precious metal(Co-Cr alloy, Ni-Cr alloy, and Co-Cr-Ti alloy) were divided into six groups: group 1(sandblaster), group 2(group 1+hard stone), group 3(group 2+electrolytic polisher), group 4(group 3+brown hard rubber point), group 5(group 4+green hard rubber point), and group 6(group 5+rouge). Considering factors affecting the rate of abrasion, the same dentist applied each finishing and polishing procedure. In addition, the surface roughness of enamel, resin, and porcelain was evaluated. The effect of finishing and polishing procedures on surface roughness of precious and non-precious metals, enamel, resin, and porcelain was evaluated by means of Atomic Force Microscope(AutoProbe CP. Park Scientific Instruments, U.S.A.) that can image the three dimensional surface profile and measure average surface roughness values of each sample at the same time. The obtained results were as follows : 1. According to finishing and polishing procedures, the surface roughness of type III gold alloy, ceramic gold alloy, and Ag-Pd alloy was decreased in the order of group 1, 2, 3, 4, and 5 (P<0.01). 2. According to finishing and polishing procedures. the surface roughness of Co-Cr alloy, Ni-Cr alloy, and Co-Cr-Ti alloy was decreased in the order of group 1, 2, 3, 4, 5, and 6 (p<0.01). 3. There was not statistically significant difference in the surface roughness among three metals of precious metals in group 1 but was significant difference in group 2, 3, 4, and 5 (P<0.05). 4. There was not statistically significant difference in the surface roughness among three metals of non-precious metals in all groups. 5. When the surface roughness of the smoothest surface of each metal, enamel. porcelain, and resin was compared, porcelain was the smoothest and the surface roughness was decreased in the order of Ni-Cr alloy. Co-Cr alloy. Co-Cr-Ti alloy, resin. Ag-Pd alloy, ceramic gold alloy type III gold alloy, and enamel (P<0.01). The results of this study indicate that the finishing and polishing procedures should be carried out in a logical, systematic sequence of steps and the harder non-precious metals may be less resistance to abrasion than are the softer precious metals.

• 자원리싸이클링
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• 제31권4호
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• pp.19-25
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• 2022

본 연구에서는 텅스텐산암모늄(APT, Ammonium Paratungstate, (NH₄)₁₀[W₁₂O₄₆H₁₀])이 사용되지 않는 친환경 초경합금 슬러지 재활용 공정을 통해 초경합금 주원료인 텅스텐 탄화물 분말을 합성하고자 하였다. 초경합금 슬러지에 대한 산 처리를 통해 텅스텐산(H₂WO₄) 추출 및 결정화를 수행하고 결정화된 텅스텐산을 텅스텐 탄화물의 원료로 사용하였다. H₂WO₄에 대한 탄화환원을 통해 텅스텐탄화물 (WC) 분말이 합성되었고 합성된 WC 분말은 200~700nm 수준의 결정립으로 구성되어 있음이 확인되었다. 이는 현재 절삭공구로 가장 널리 사용되는 1~3㎛ 입도의 상용 WC 분말에 비해 미세한 것으로 텅스텐 금속 분말에 대한 고온(1,700℃ 이상) 고상 탄화법을 통해 제조되는 상용 WC 분말과 달리 H₂WO₄ 나노 결정립에 대한 탄화환원을 통해 WC 분말이 합성되었기 때문으로 사료된다. H₂WO₄로 부터 합성된 WC 분말의 경우 탄화환원에 의해 탄소의 제거가 수월하여 상용 WC 분말에 비해 잔류 탄소가 적은 것으로 확인되었으며 작은 결정립 크기로 인해 초경합금 원료로 사용되었을 때 WC-Co 복합체 내 WC 입자의 성장이 활발하게 일어나 H₂WO₄로부터 합성된 WC 분말이 적용된 WC-Co 복합체의 경우 WC 입자가 조대하고 파괴인성이 우수한 것으로 확인되었다.