• 한국분말재료학회지
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• 제21권2호
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• pp.93-96
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• 2014

Cobalt coated tungsten carbide-cobalt composite powder has been prepared through wet chemical reduction method. The cobalt sulfate solution was converted to the cobalt chloride then the cobalt hydroxide. The tungsten carbide powders were added in to the cobalt hydroxide, the cobalt hydroxide was reduced and coated over tungsten carbide powder using hypo-phosphorous acid. Both the cobalt and the tungsten carbide phase peaks were evident in the tungsten carbide-cobalt composite powder by X-ray diffraction. The average particle size measured via scanning electron microscope, particle size analysis was around 380 nm and the thickness of coated cobalt was determined to be 30~40 nm by transmission electron microscopy.

• 한국분말재료학회지
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• 제23권5호
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• pp.364-371
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• 2016

This study investigates the thermal shock property of a polycrystalline diamond compact (PDC) produced by a high-pressure, high-temperature (HPHT) sintering process. Three kinds of PDCs are manufactured by the HPHT sintering process using different particle sizes of the initial diamond powders: $8-16{\mu}m$ ($D50=4.3{\mu}m$), $10-20{\mu}m$ ($D50=6.92{\mu}m$), and $12-22{\mu}m$ ($D50=8.94{\mu}m$). The microstructure observation results for the manufactured PDCs reveal that elemental Co and W are present along the interface of the diamond particles. The fractions of Co and WC in the PDC increase as the initial particle size decreases. The manufactured PDCs are subjected to thermal shock tests at two temperatures of $780^{\circ}C$ and $830^{\circ}C$. The results reveal that the PDC with a smaller particle size of diamond easily produces microscale thermal cracks. This is mainly because of the abundant presence of Co and WC phases along the diamond interface and the easy formation of Co-based (CoO, $Co_3O_4$) and W-based ($WO_2$) oxides in the PDC using smaller diamond particles. The microstructural factors for controlling the thermal shock property of PDC material are also discussed.

• Journal of Welding and Joining
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• 제18권3호
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• pp.51-59
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• 2000

Sink roll has been used in molten 55%Al-Zn alloy bath of continuous galvanizing line for sinking and stabilizing working steel strip in molten metal bath. In the process, the sink roll body inevitably build up dross compounds and pitting on the sink roll surface during 55%Al-Zn alloy coated strip production, and the life time of the sink roll is shorten by build up dross compounds and pitting. The present study examined the application of thermally sprayed ceramic coatings method on sink roll body for improving erosion resistance at molten 55% Al-Zn pool. In this experiment, the stainless steels such as STS 316L and STS 430F were used as the substrate materials. The CoNiCr and WE-Co powder were selected as bond coating materials. Moreover $Al_2O_3-ZrO_2-SiO_2 and ZrO_2-SiO_2$ powders selected as the top coating materials. Appearances of the specimens before and after dipping to molten 55%Al-Zn pool were compared and analyzed. As a result of this study, STS430F of substrate, WC-Co of bond spray coatings, $ZrO_2-SiO_2$ power of top spray coatings is the best quality in erosion resistance test at molten 55%Al-Zn pool

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.97.2-97.2
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• 2018

This study formed a hard TiAlSiWN coating layer using Ti, Al, Si and W raw powders that were mechanically alloyed and refined. The TiAlSi and TiAlSiW coating targets were fabricated using a single PCAS process in a short time with the optimal sintering conditions. The coating targets were deposited on the WC substrate by forming coating layers using TiAlSiN and TiAlSiWN nitride nano-composite structures with an AIP process. The properties of the nitride nano-composite coating layers were compared according to the addition of W. The microstructure of the nitride nano-composite coating layer was analyzed, focusing on the distribution of the crystalline phases, amorphous phases ($Si_3N_4$), and growth orientation of the columnar crystal depending on the addition of W. The mechanical properties of the coating layers were exhibited a hardness of approximately $3,000kg/mm^2$ and adhesion of about 117.77N in the TiAlSiN. In particular, the TiAlSiWN showed excellent properties with a hardness of more than $4,300kg/mm^2$ and an adhesion of about 181.47N.

• 한국분말재료학회지
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• 제23권4호
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• pp.282-286
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• 2016

A sintered body of $TiB_2$-reinforced iron matrix composite ($Fe-TiB_2$) is fabricated by pressureless-sintering of a mixture of titanium hydride ($TiH_2$) and iron boride (FeB) powders. The powder mixture is prepared in a planetary ball-mill at 700 rpm for 3 h and then pressurelessly sintered at 1300, 1350 and $1400^{\circ}C$ for 0-2 h. The optimal sintering temperature for high densities (above 95% relative density) is between 1350 and $1400^{\circ}C$, where the holding time can be varied from 0.25 to 2 h. A maximum relative density of 96.0% is obtained from the ($FeB+TiH_2$) powder compacts sintered at $1400^{\circ}C$ for 2 h. Sintered compacts have two main phases of Fe and $TiB_2$ along with traces of TiB, which seems to be formed through the reaction of TiB2 formed at lower temperatures during the heating stage with the excess Ti that is intentionally added to complete the reaction for $TiB_2$ formation. Nearly fully densified sintered compacts show a homogeneous microstructure composed of fine $TiB_2$ particulates with submicron sizes and an Fe-matrix. A maximum hardness of 71.2 HRC is obtained from the specimen sintered at $1400^{\circ}C$ for 0.5 h, which is nearly equivalent to the HRC of conventional WC-Co hardmetals containing 20 wt% Co.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2003년도 춘계학술강연 및 발표대회
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• pp.35-35
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• 2003

)를 금속와이어에 인가하면 저항발열에 의해 와이어가 미세한 입자나 금속증기상태로 폭발하는 현상을 이용한 것으로 기상합성법에 속한다고 할 수 있다. 선폭법은 다른 제조법에 비해 공정이 간단하여 생산비용이 저렴하며, 원재료의 조성을 갖는 분말의 합성과 금속간화합물, 융점차이가 나는 재료의 합금화 등이 가능하다. 인가에너지의 크기와 폭발 시 분위기를 제어함으로써 분말의 평균크기와 분포 제어 또한 가능하다. 본 연구는 러시아의 우수한 기초기술을 바탕으로 Pb-Sn계 합금은 전기폭발법으로 극미세분말을 제조하였으며, 분말의 형상, 상 화학조성의 변화를 조사하였다. 본 실험에 사용된 Sn-Pb계(All-Union State Standard 1499-70, 0.53mm)합금와이어는 자동시스템(1-0.6Hz)에 의해 챔버안으로 공급되었다. 이 때 임계폭발 와이어 길이는 50-80nm으로 실험을 행하였다. 챔버 압력은 1.4~2.0atm으로 유지하였다. 제조된 분말의 특성은 XRD, XRPES, SEM등을 이용하여 분말의 형상과 상, 화학조성, 표면분석을 행하였으며 DSC, TGA, BET분석을 통하여 온도변화에 따른 금속분말의 열량변화, 질량변화, 비표면적을 측정하였다. 제조된 Sn-Pb계 분말은 모두 평균 입도 117nm~220nm의 구형형상이었다. 이때 합금분말의 조성은 51.17~63.21 at%Sn, 35.47~46.37 at%Pb로 나타났다. 와이어에 인가되는 비에너지(W/Wc)가 감소된에 EK라 표면층의 Pb함량이 증가함을 보였다. 이는 와이어 내부 저항의 감소로 인한 공정시간의 지연과 Sn, Pb의 확산계수 차이에 의한 것으로 사료된다. 열분석 결과, Sn~Pb계 화합물의 융점은 167~$169^{\circ}C$로 관찰되었으며, $10^{\circ}C$/min로 $920^{\circ}C$까지 승은 하였을 때 17.1~18 wt%의 질량증가를 보였다.TEX>계 나노복합분말이 얻어짐을 알 수 있었다. 이 때 X션 회절피크의 line broadening으로부터 복합분말의 Fe 명균 결정립 크기는 24nm로 초미세 결정럽의 분말합금이었다. 포화자화값은 볼밀처리에 따라 점점 증가하여 MA 30시간에는 20.3emu/g로 포화됨을 알 수 있었다. 또한 보자력 Hc는 MA초기단계에 350e로 매우 낮으나 30시간 후에는 Hc값이 2600e로 매우 큰 값을 나타내었다. 이것은 환원반응결과 초기에 생성된 Fe의 결정립이 비교적 크고 결정결함이 적으나 볼밀처리를 30시간까지 행하면 Fe 결정렵의 미세화 빛 strain 증가로 magnetic hardening이 일어나기 때문인 것으로 사료된다.길이가 50, 30cm인 압출재를 제조하였다. 열간압출한 후의 미세조직을 광학현미경으로 압출방향에 평행한 방향과 수직방향으로 관찰하였고, 열간 압출재 이방성을 검토하기 위하여 X선 회절분석을 실실하여 결정방위를 확인하였다. 전기 비저항 및 Seebeck 계수 측정을 위하여 각각 2$\times$2$\times$10$mm^3$ 그리고 5$\times$5$\times$10TEX>$mm^3$ 크기의 시편을 준비하였다.준비하였다.전류를 구성하는 주요 입자의 에너지 영역(75~l13keV)에서 가장 높은(0.80) 상관계수를 기록했다. 넷째, 회복기 중에 일어나는 입자들의 유입은 자기폭풍의 지속시간을 연장시키는 경향을 보이며 큰 자기폭풍일수록 현저했다. 주상에서 관측된 이러한 특성은 서브스톰 확장기 활동이 자기폭풍의 발달과 밀접한 관계가 있음을 시사한다.se that were all low in two aspects, named "the Nonsignificant group". And the issues were high risk perception in general setting and lo