• 한국분말재료학회지
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• 제1권2호
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• pp.119-198
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• 1994

The characteristics of various important microstructural factors of WC-base hard- metals (cemented carbides) such as the amount of Co metal binder phase, the carbide grain size, the microstructural defects acting as a fracture source, the solid solubility of tungsten in the binder phase affected by the carbon content, the precipitation of $Co_3W$, the domain size of binder phase, the formation of ${\beta}-free$ layer or Co-rich layer and CVD or PVD coated layer, and the effects of these factors on the flexural strength of the hardmetals are reviewed.

• 유변학
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• 제11권1호
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• pp.57-65
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• 1999

분말사출재의 항복응력을 효과적이고 간단한 방법으로 측정하기 위해서 수차 장치를 사용한 항복응력 측정장치를 개발하였다. 수차 방식은 벽면 미끄러짐을 고려할 필요가 없는 장점이 있으나 전단률에 따른 점도 변화 측정에는 사용할 수 없는 단점도 있다. 수차 장치의 타당성 검토를 선형유체를 사용하여 검증하였으며, 수차 장치의 양단에서 나타나는 오차도 실험적으로 확인하였다. 분말 현탁액의 일반적인 특징이라고 여겨지는 항복 시 발생하는 순간 최대 토오크는 측정 장치의 제어기 특성에 따른 영향이 큰 것을 확인하고 안정 토오크 영역을 항복응력 계산의 기준으로 결정하였다. 측정되는 토오크에서 수차의 회전 저항에 따른 효과를 제거하기 위해 다양한 속도에서 측정된 토오크를 선형함수로 근사하여 회전 속도가 없을 때의 토오크를 얻었다. 측정 방법의 일반적인 검증을 위해 텅스텐 카바이드 분말과 왁스계 바인더를 이용한 분말사출재의 항복응력을 온도와 분말 충전률 변화에 따라서 측정하였다.

• 한국분말재료학회지
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• 제6권4호
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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.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.89-90
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• 2006

Austenitic stainless steel has been used as a corrosion resistance material. However, austenitic stainless steel has poor wear resistance property due to its low hardness. In this investigation, we apply powder composite process to obtain hard layer of Stainless steel. The composite material was fabricated from planetary ball milled SUS316L stainless steel powder and WC powder and then sintered by Pulsed Current Sintering (PCS) method. We also added TiC powder as a hard particle in WC layer. Evaluations of wear properties were performed by pin-on-disk wear testing machine, and a remarkable improvement in wear resistance property was obtained.

• 한국분말재료학회지
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• 제3권3호
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• pp.167-173
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• 1996

The effect of ball milling on the pressureless sintering of MoSi$_2$ was investigated. Ball milling was conducted at 70 rpm for 72 hours using different balls and vessels: one used tungsten carbide balls in a plastic vessel(referred as B-powder) and the other stainless steel ball in a stainless steel vessel(referred as C- powder). The powder was compacted with 173MPa and subsequently sintered at the temperature range of 1150 $^{\circ}C$ and 1450 $^{\circ}C$ in H$_2$, atmosphere. Sintered density was measured and scanning electron micrograph was observed. Over 90% of the theoretical density was attained at 1250 $^{\circ}C$ within 10 minutes for C-powders, while the similar densification required a sintering temperature of 1450 $^{\circ}C$ for B-powders. Such a difference in sinterability between B and C-powders was discussed in terms of the effect of particle size reduction and activated sintering caused by Ni and/or Fe introduced during ball milling.

• 한국분말재료학회지
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• 제11권2호
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• pp.124-129
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• 2004

Nanosized WC and WC-Co powders were synthesised by chemical vapor condensation(CVC) process using the pyrolysis of tungsten hexacarbonyl(W(CO)$_6$) and cobalt octacarbonyl(Co$_2$(CO)$_8$). The microstructural changes and phase evolution of the CVC powders during post heat-treatment were studied using the XRD, FE-SEM, TEM, and ICP-MS. CVC powders were consisted of the loosely agglomerated sub-stoichimetric WC$_{1-x}$ and the long-chain Co nanopowders. The sub-stochiometric CVC WC and WC-Co powders were carburized using the mixture gas of CH$_4$-H$_2$ in the temperature range of 730-85$0^{\circ}C$. Carbon content of CVC powder controlled by the gas phase carburization at 85$0^{\circ}C$ was well matched with the theoretical carbon sioichiometry of WC, 6.13 wt％. During the gas phase carburization, the particle size of WC increased from 20 nm to 40 nm and the long chain structure of Co powders disappeared.

• 한국기계가공학회지
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• 제3권1호
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• pp.15-21
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• 2004

The machining process of ceramics can be characterized by cracking and brittle fracture. In the machining of ceramics, edge chipping and crack propagation are the principal reasons to cause surface integrity deterioration. Such phenomenon can cause not only poor dimensional and geometric accuracy, but also possible failure of the ceramic parts. Thus, traditional ceramics are very difficult-to-cut materials. To overcome such problems, in this paper, h-BN powder, which gives good cutting property, is added for the fabrication of machinable ceramics by volume of 5, 10, 15, 20, 25 and 30%. The objectives of this paper is to evaluate the fracture phenomenon of the tungsten carbide tool and the variation of surface integrity of the manufactured machinable ceramics under various cutting conditions during end mill machining With CNC machining center.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.293-294
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• 2006

Laser Powder Deposition (LPD) is a technology capable of modifying a metallic structure by adding the appropriate material to perform a desired function. LPD offers a unique fabrication technique that allows the use of soft (tough) materials as base structures. Through LPD a hard material can be applied to the base material with little thermal input (minimal dilution and heat-affected-zone {HAZ}), thus providing the function of a heat treatment or other surface modifications. These surface modifications have been evaluated through standard wear testing (ASTM G-65), surface hardness (Rc), micro-hardness (vickers), and optical microscopy.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2007년도 추계학술대회 논문집
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• pp.1-2
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• 2007

• 한국분말재료학회지
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• 제25권3호
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• pp.240-245
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• 2018

This study focuses on the fabrication of a WC/Co composite powder from the oxide of WC/Co hardmetal scrap using solid carbon in a hydrogen gas atmosphere for the recycling of WC/Co hardmetal. Mixed powders are manufactured by mechanically milling the oxide powder of WC-13 wt% Co hardmetal scrap and carbon black with varying powder/ball weight ratios. The oxide powder of WC-13 wt% Co hardmetal scrap consists of $WO_3$ and $CoWO_4$. The mixed powder mechanically milled at a lower powder/ball weight ratio (high mechanical milling energy) has a more rapid carbothermal reduction reaction in the formation of WC and Co phases compared with that mechanically milled at a higher powder/ball weight ratio (lower mechanical milling energy). The WC/Co composite powder is fabricated at $900^{\circ}C$ for 6 h from the oxide of WC/Co hardmetal scrap using solid carbon in a hydrogen gas atmosphere. The fabricated WC/Co composite powder has a particle size of approximately $0.25-0.5{\mu}m$.