• 한국재료학회지
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• 제4권4호
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• pp.393-400
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• 1994

1$\mu \textrm{m}$이하의 텅스텐 분말에 구리를 균일하게 코팅하는 공정을 새로이 개발했다. 구리가 코팅된 $\mu \textrm{m}$이하의 텅스텐 분말을 이용하여 액상소결하였으며, 구리가 균일하게 분포된 W-Cu합금을 얻을 수있었다. 본 연구에서 개발된 방법에 의해 구리의 함유량을 10wt.%이하로 낮추면서도 균일한 W-Cu합금을 얻을 수 있었으며, 특히 코발트를 같은 방식에 의해 첨가하면 구리액상이 형성된 후 급격히 치밀화하여 96% 이상의 상대밀도를 갖는 W-Cu 합금을 제작하는데 성공하였다. 코발트 첨가에 의한 급격한 치밀화의 증가는 텅스텐과 구리액상 사이의 접착성 향상에 기인하는 것으로 밝혀졌다.

• Nuclear Engineering and Technology
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• 제53권5호
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• pp.1593-1601
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• 2021

Oxide dispersion strengthening (ODS) tungsten alloys are highly desirable in irradiation applications. However, how to improve the properties of ODS-tungsten alloys efficiently has been worth studying for a long time. Here we report a nanostructuring approach that achieves W-La₂O₃ alloy with a high level of flexural strength and Vickers hardness at room temperature, which have the maximum value of 581 MPa and 703 Hv, respectively. This method named solution combustion synthesis (SCS) can generate 30 nm coating structures W-La₂O₃ composite powders by using Keggin-type structural polyoxometalates as raw materials in a fast and low-cost process. The composite powder can be fabricated to W-La₂O₃ alloy with an optimal microstructure of submicrometric W grains coexisting with nanometric oxide particles in the grain interior, and a stability interface structure of grain boundaries (GBs) by forming transition zones. The method can be used to prepare new ODS alloys with excellent properties in the future.

• 한국분말재료학회지
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• 제29권5호
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• pp.376-381
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• 2022

Tungsten disulfide (WS₂) nanosheets have attracted considerable attention because of their unique optical and electrical properties. Several methods for fabrication of WS₂ nanosheets have been developed. However, methods for mass production of high-quality WS₂ nanosheets remain challenging. In this study, WS₂ nanosheets were fabricated using mechano-chemical ball milling based on the synergetic effects of chemical intercalation and mechanical exfoliation. The ball-milling time was set as a variable for the optimized fabricating process of WS₂ nanosheets. Under the optimized conditions, the WS₂ nanosheets had lateral sizes of 500-600 nm with either a monolayer or bilayer. They also exhibited high crystallinity in the 2H semiconducting phase. Thus, the proposed method can be applied to the exfoliation of other transition metal dichalcogenides using suitable chemical intercalants. It can also be used with high-performance WS₂-based photodiodes and transistors used in practical semiconductor applications.

• 한국분말재료학회지
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• 제30권5호
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• pp.436-441
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• 2023

Molybdenum-tungsten (Mo-W) alloy sputtering targets are widely utilized in fields like electronics, nanotechnology, sensors, and as gate electrodes for TFT-LCDs, owing to their superior properties such as high-temperature stability, low thermal expansion coefficient, electrical conductivity, and corrosion resistance. To achieve optimal performance in application, these targets' purity, relative density, and grain size of these targets must becarefully controlled. We utilized nanopowders, prepared via the Pechini method, to obtain uniform and fine powders, then carried out spark plasma sintering (SPS) to densify these powders. Our studies revealed that the sintered compacts made from these nanopowders exhibited outstanding features, such as a high relative density of more than 99%, consistent grain size of 3.43 ㎛, and shape, absence of preferred orientation.

• 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.

• 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.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1997년도 제26회 추계학술대회
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• pp.211-216
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• 1997

The tungsten disulfide (WS$_2$) solid lubricant was synthesized by two different reaction processes, and the chemical and physical characteristics of synthesized WS$_2$ powder were analyzed in terms of the average particle size, morphology, crystalline phase. The solid WO$_3$ powder with the average size of 0.2 $\mu$m was reacted with CS$_2$ gas flowed with N$_2$ or 96% N$_2$ + 4% H$_2$ forming gas for 36 h and 24 h at 900$\circ$C respectively. In the case of vapour phase transport method, the 3.5 wt% iodine was added as a vapour transport reagent into the composition of tungsten and sulfur powders maintaining a constant molar ratio of W : S = 1 : 2.2. The mixture was then heat treated at 850$\circ$C for 2 weeks in vacuum The reaction product obtained showed the average size of 12 $\mu$m and the hexagonal plate shape of typical solid lubricant with 2H-WS$_2$ crystalline phase.

• 한국분말재료학회지
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• 제1권2호
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• pp.167-173
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• 1994

Cu-10wt%W composite powders have been manufactured by a high energy ball milling technique. The composite powders were pressed at 250 MPa and sintered in a dry hydrogen at 103$0^{\circ}C$ for 4 hours. After sintering, Cu-10wt%W composite materials were forged. And the arc-resistance of forged materials which have the same relative density of 94% has been tested. Composite particles, i.e. tungsten particles distributed homogeneously in the copper matrix, was formed after 480 min mechanical alloying. Densities of these sintered materials were ranged from 74 to 84%. Densification degree was due to the formation of composite powders. As the mechanical alloying time increased, the hardness was increased and tungsten particle size was decreased. Arc loss of the forged specimens was decreased as increasing the mechanical alloying time.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.857-858
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• 2006

In order to clarify the wear resistance as cutting tools, the effect of oxygen addition on oxidation behavior of the ${\beta}-Si_3N_4$ ceramics with 5 mass% $Y_2O_3$ and 2 or 4 mass% $Al_2O_3$ was investigated by performing oxidation tests in air at $1300^{\circ}$ to $1400^{\circ}C$ and cutting performance tests. From test results, we could conclude that the mechanical properties of ${\beta}-Si_3N_4$ ceramics depending on oxygen introduction are much effective on cutting performance improvements of ${\beta}-Si_3N_4$ ceramics.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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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.