• 대한금속재료학회지
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• 제48권7호
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• pp.630-638
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• 2010

The present investigation has been performed on the mixing behavior and microstructural development during fabrication of Fe micro-nano powder feedstock for a micro-powder injection molding process. The mixing experiment using a screw type blender system was conducted to measure the variations of torque and temperature during mixing of Fe powder-binder feedstock with progressive powder loading for various nano-powder compositions up to 25%. It was found that the torque and the temperature required in the mixing of feedstock increased proportionally with increasing cumulative powder loading. Such an increment was larger in the feedstock containing higher content of nano-powder at the same powder loading condition. However, the maximum value was obtained at the nano-powder composition of not 25% but 10%. It was owing to the 'roller bearing effect' of agglomerate type nano-powder acting as lubricant during mixing, consequently leading to the rearrangement of micro-nano powder in the feedstock. It is concluded that the improvement of packing density by rearrangement of nano-powders into interstices of micro-powders is responsible for the maximum powder loading of about 71 vol.% in the nano-powder composition of 25%.

• Tribology and Lubricants
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• 제34권6호
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• pp.235-240
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• 2018

Superlubricity refers to the lubrication phenomenon that occurs when the friction coefficient is lower than 0.01. In recent years, this phenomenon has received a significant amount of attention because it can greatly contribute to the reduction of economic and environmental losses caused by friction and wear. In the case of acid lubricants, only ceramic materials can be used for superlubricity, and it takes a long running-in period to enter the superlubricity regime. In this work, we investigated the superlubricity effect of vitreous enamel coating on SUS304. We also examined the running-in period of vitreous enamel coating under phosphoric acid lubricant condition with respect to surface treatments. Drying and polishing methods were used to treat the vitreous enamel coating on the specimen. The friction experimental results revealed that superlubricity could be achieved with vitreous enamel coating. It was also found that the drying and polishing methods can significantly reduce the running-in period and improve the wear properties of vitreous enamel coating. In particular, the polishing method shortened the running-in period by approximately 99% and reduced the wear rate by approximately 99%, compared to nontreated vitreous enamel coating.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2001년도 춘계학술발표회 초록집
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• pp.3-3
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• 2001

Recently TiN, TiAlN, CrN hardcoatings have adapted many industrial application such as die, mold and cutting tools because of good wear resistant and thermal stability. However, in terms of high speed process, general hard coatings have been limited by oxidation and thermal hardness drop. Especially in the case of PCB drill, high speed cutting and without lubricant process condition have not adapted these coatings until now. Therefore more recently, superhard nanocomposite coating which have superhard and good thermal stability have developed. In previous works, WC-TiAlN new nanocomposite film was investigated by cathodic arc ion plating system. Control of AI concentration, WC-TiAlN multi layer composite coating with controlled microstructure was carried out and provides additional enhancement of mechanical properties as well as oxidation resistance at elevated temperature. It is noted that microhardness ofWC-TiA1N multi layer composite coating increased up to 50 Gpa and got thermal stability about $900^{\circ}C$. In this study WC-TiAlN nanocomposite coating was deposited on PCB drill for enhancement of life time. The parameter was A1 concentration and plasma cleaning time for edge sharpness maintaining. The characteristic of WC-TiAlN film formation and wear behaviors are discussed with data from AlES, XRD, EDS and SEM analysis. Through field test, enhancement of life time for PCB drill was measured.

• 한국산학기술학회논문지
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• 제6권6호
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• pp.468-472
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• 2005

유리병의 제조에 있어서 유리 융체가 금형 벽면에 부착하는 것을 방지하기 위하여 성형할 때마다 금형 내벽면을 윤활제로 도포하는 공정이 있다. 금형 벽면을 통기성이 있는 다공질 소결체로 제조하면 도포공정을 생략할 수 있다. 따라서 본 연구에서는 스테인리스 중에서 내열${\cdot}$내마모 특성이 가장 우수한 310L계 조대 분말($-150{\mu}m$) 및 420J2 계 미세 분말($40{\~}50{\mu}m$)을 사용, 유리 금형용 내벽면 재로서 가장 적합한 다공질 소결체(소결체의 밀도: $85{\~}90\%$)를 제작하기 위하여 성형압력, 소결 분위기, 소결온도 및 시간을 변화시켜 다음과 같은 결과를 얻었다. (1) 고상 소결로서는 입자 크기가 큰 310L분말을 가지고는 어느 경우에 있어서나, 목적하는 소결 밀도를 얻을 수 없었다. (2) $2ton/cm^2$의 성형압력으로 성형한 실형상 성형체를 양산용 진공($1300^{\circ}C$, 2시간) 소결로에서 소결한 결과, 소결체의 밀도는 $310L+0.03\%B$, 420J2, 420J2+(0.03, 0.06)$\%$B에서 각각 6.2(79$\%$), 6.6(86$\%$), 7.3(95$\%$), $7.6(99\%)g/cm^3$로 나타났다. 따라서, 420J2계 분말(저압성형) 및 310L+0.03$\%$B(고압성형)분말을 사용하여 진공 중 소결하면 목적하는 통기도를 가진 소결체를 제작할 수 있다는 것을 알았다.

• 농업과학연구
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• 제6권2호
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• pp.125-133
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• 1979

평창군(平昌郡)에 발생(發生)한 산사태지(山沙汰地)의 유형(類型)은 다음과 같으며 그특징(特徵)을 보면, 1. 석회암(石灰岩) 심토지대(深土地帶) 토양단면상(土壤斷面上)에 점토(粘土)의 집적(集積)으로 토성(土性)의 차이(差異)가 뚜렷하여 수분(水分)에 의한 윤활작용(潤滑作用)으로 니류형산사태(泥流型山沙汰)가 발생(發生)한다. 2. 석회암(石灰岩) 암반지대(岩盤地帶) 표토(表土)의 두께가 얇고 평활(平滑)한 암반층(岩盤層)이 존재(存在)하므로 집중호우시(集中豪雨時) 표층토(表層土)가 쉽게 포화(飽和)되고 암반경계부(岩盤境界部)에 수분윤활작용(水分潤滑作用)으로 표토(表土)가 분리(分離) 붕락(崩落)한다. 3. 화강암지대(花崗岩地帶) 조립질토성(粗粒質土性)의 모재(母材)는 응집력(凝集力)이 적으며 공극(孔隙)이 많고 삼투능이 커서 수분(水分)에 의한 식화(蝕和) 및 분리작용(分離作用)이 신속하여 쉽게 기암층(基岩層)으로부터 붕락(崩落) 계안(溪岸)을 침식(浸蝕)한다. 본지역(本地域)의 산사태예방책(山沙汰豫防策)으로 다음을 들 수 있다. 1. 산사태근원지(山沙汰根源地)의 집중조림(集中造林) 및 사방공작물(砂防工作物) 설치(設置). 2. 급경사지(急傾斜地)($25^{\circ}$이상)의 개벌(皆伐) 및 개간경작(開墾耕作)의 억제(抑制) 3. 산사태방비림(山沙汰防備林) 조성(造成).

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2000년도 춘계학술강연 및 발표대회 강연 및 발표논문 초록집
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• pp.9-10
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• 2000

An important business-field of world-wide steel-industry is the coating of thin metal-sheets with zinc, zinc-aluminum and aluminum based materials. These products mostly go into automotive industry. in particular for the car-body. into building and construction industry as well as household appliances. Due to mass-production, the processing is done in large continuously operating plants where the mostly cold-rolled metal-strip as the substrate is handled in coils up to 40 tons unwind before and rolled up again after passing the processing plant which includes cleaning, annealing, hot-dip galvanizing / aluminizing and chemical treatment. In the liquid Zn, Zn-AI, AI-Zn and AI-Si bathes a combined action of corrosion and wear under high temperature and high stress onto the transfer components (rolls) accounts for major economic losses. Most critical here are the bearing systems of these rolls operating in the liquid system. Rolls in liquid system can not be avoided as they are needed to transfer the steel-strip into and out of the crucible. Since several years, ceramic roller bearings are tested here [1.2], however, in particular due to uncontrollable Slag-impurities within the hot bath [3], slide bearings are still expected to be of a higher potential [4]. The today's state of the art is the application of slide bearings based on Stellite\ulcorneragainst Stellite which is in general a 50-60 wt% Co-matrix with incorporated Cr- and W-carbides and other composites. Indeed Stellite is used as the bearing-material as of it's chemical properties (does not go into solution), the physical properties in particular with poor lubricating properties are not satisfying at all. To increase the Sliding behavior in the bearing system, about 0.15-0.2 wt% of lead has been added into the hot-bath in the past. Due to environmental regulations. this had to be reduced dramatically_ This together with the heavily increasing production rates expressed by increased velocity of the substrate-steel-band up to 200 m/min and increased tractate power up to 10 tons in modern plants. leads to life times of the bearings of a few up to several days only. To improve this situation. the Mechanical Alloying (MA) TeChnique [5.6.7.8] is used to prOduce advanced Stellite-based bearing materials. A lubricating phase is introduced into Stellite-powder-material by MA, the composite-powder-particles are coated by High Energy Milling (HEM) in order to produce bearing-bushes of approximately 12 kg by Sintering, Liquid Phase Sintering (LPS) and Hot Isostatic Pressing (HIP). The chemical and physical behavior of samples as well as the bearing systems in the hot galvanizing / aluminizing plant are discussed. DependenCies like lubricant material and composite, LPS-binder and composite, particle shape and PM-route with respect to achievable density. (temperature--) shock-reSistibility and corrosive-wear behavior will be described. The materials are characterized by particle size analysis (laser diffraction), scanning electron microscopy and X-ray diffraction. corrosive-wear behavior is determined using a special cylinder-in-bush apparatus (CIBA) as well as field-test in real production condition. Part I of this work describes the initial testing phase where different sample materials are produced, characterized, consolidated and tested in the CIBA under a common AI-Zn-system. The results are discussed and the material-system for the large components to be produced for the field test in real production condition is decided. Outlook: Part II of this work will describe the field test in a hot-dip-galvanizing/aluminizing plant of the mechanically alloyed bearing bushes under aluminum-rich liquid metal. Alter testing, the bushes will be characterized and obtained results with respect to wear. expected lifetime, surface roughness and infiltration will be discussed. Part III of this project will describe a second initial testing phase where the won results of part 1+11 will be transferred to the AI-Si system. Part IV of this project will describe the field test in a hot-dip-aluminizing plant of the mechanically alloyed bearing bushes under aluminum liquid metal. After testing. the bushes will be characterized and obtained results with respect to wear. expected lifetime, surface roughness and infiltration will be discussed.