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Page : 263 - 269
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- 구리합금에 대한 WC-27NiCr 초고속화염용사 코팅층의 해수내 캐비테이션 특성 평가
- Copper alloys are commonly applied to ship\\\'s propellers, pumps and valves which are serviced in seawater due to their good castability and corrosion resistance. In the environment of high flow velocity, however, erosion damage predominates over corrosion damage. In particular, the cavitation in seawater environment accelerates
surface damage to copper alloys, resulting in degradation of products and economic losses and also threatening safety. The surface was coated with WC-27NiCr by high velocity oxygen fuel(HVOF) spraying technique to attain durability and cavitation resistance of copper alloys under high velocity/pressure flow. The cavitation test
was performed for the WC-27NiCr coating deposited by HVOF in seawater at the amplitude of 30 μm with seawater temperature. The cavitation at 15 ℃ caused exfoliation of the coating layer in 17.5 hours while that of 25 ℃ caused the exfoliation in 12.5 hours. When the temperature of seawater was elevated to 25 ℃ from 15 ℃, more damage was induced by over 160%. Although WC-27NiCr has good durability, corrosion resistance and eletrochemical stability, the cavitation damage rate of the coating layer could remarkably increase at the elevated temperatures under cavitation environments. - KEYWORDs : copper alloy, high velocity oxygen fuel(HVOF), cavitation, WC-27NiCr coating, exfoliation
- AUTHORs : 한민수? 김민성? 장석기? 김성종†
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Page : 270 - 274
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- 철근 콘크리트 구조물용 다기능 멀티센서의 부식 모니터링에 관한 연구: Part 1
- This study represents the result of corrosion monitoring on reinforced concrete specimens by means of multi-functional corrosion monitoring sensors. To confirm the effectiveness of the sensors, eight different kinds of condition were adopted. Test factors were corrosion potential, current, corrosion rate, resistivity, and temperature, which were monitored with the sensors. Through this study, judging corrosion of steel in concrete with single corrosion factor such as corrosion potential was difficult, because many other factors can have an influence on the reaction of corrosion. By using three different kinds of sensors, it could enhance the accuracy of corrosion monitoring.
- KEYWORDs : corrosion sensor, monitoring, reinforced concrete, corrosion potential
- AUTHORs : 진충국? 정진아†? 경은진
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Page : 275 - 279
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- 나노결정질 Ni-W 합금전착의 내부응력에 미치는 공정조건 변수의 영향
- Ni-W alloy deposits have lately attracted the interest as an alternative surface treatment method for hard chromium electrodeposits because of higher wear resistance, hardness at high temperature, and corrosion resistance. This
study deals with influences of process variables, such as electodeposition current density, plating temperature and pH, on the internal stress of Ni-W nanocrystalline deposits. The internal stress was increased with increasing the applied current density. With increasing applied current density, the grain size of the deposit decreases and concentration of hydrogen in the deposit increases. The subsequent release of the hydrogen results in shrinkage of the deposit and the introduction of tensile stress in the deposit. Consequently, for layers deposited at high current density, cracking occurs readily owing to high tensile stress value. By increasing the temperature of the electrodeposition from 60 ℃ to 80 ℃, the internal stress was decreased. It seems that an increase in the number of active ions overcoming the activation energy at elevated temperature caused a decline in the concentration
polarization and surface diffusion. It decreased the level of hydrogen absorption due to the lessened hydrogen evolution reaction. Therefore, the lower level of hydrogen absorption degenerated the hydride on the surface of the electrode, resulting in the reduction of the internal stress of the deposits. By increasing the pH of the
electrodeposition from 5.6 to 6.8, the internal stress in the deposits were slightly decreased. It is considered that the decrease in internal stess of deposits was due to supply of W complex compound in cathode surface, and hydrogen ion resulted from decrease of activity. - KEYWORDs : Ni-W, electroplating, internal stress, current density, nanocrystalline
- AUTHORs : 김경태†? 이정자? 황운석
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Page : 280 - 285
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- AC8A 알루미늄합금 주조재의 열처리에 의한 특성 평가
- Aluminum is on active metal, but it is well known that its oxide film plays a role as protective barrier which is comparatively stable in air and neutral aqueous solution. Thus, aluminum alloys have been widely applied in architectural trim, cold & hot-water storage vessels and piping etc., furthermore, the aluminum alloy of AC8A
have been widely used in mold casting material of engine piston because of its properties of temperature and wear resistance. In recent years, the oil price is getting higher and higher, thus the using of low quality oil has been significantly increased in engines of ship and vehicle. Therefore it is considered that evaluation of corrosion resistance as well as wear resistance of AC8A material is also important to improve its property and prolong its lifetime. In this study, the effect of solution and tempering heat treatment to corrosion and wear resistance is investigated with electrochemical method and measurement of hardness. The hardness decreased with solution heat treatment compared to mold casting condition, but its value increased with tempering heat treatment and exhibited the highest value of hardness with tempering heat treatment temperature at 190 ℃ for
24hrs. Furthermore, corrosion resistance increased with decreasing of the hardness, and decreased with increasing of the hardness reversely. As a result, it is suggested that the optimum heat treatment to improve both corrosion and wear resistance is tempering heat treatment temperature at 190 ℃ for 16hrs. - KEYWORDs : aluminum alloy, mold casting, corrosion resistance, wear resistance, solution heat treatment,
- AUTHORs : 이성열? 박동현? 원종필? 김윤해? 이명훈? 문경만? 정재현†
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Page : 1 - 6
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- Development of High Functional Black Resin Coated Electrogalvanized Steel Sheet for Digital TV Panel
- Recently Digital TV industry has drastically been moving the illuminating system, which causes an obvious product change from PDP and LCD to LED model to provide high-definition image. Due to strong competition in the digital industry, TV manufacturers make a great efforts to reduce production cost by using low-priced
materials such as steels instead of aluminum and plastic etc. In this paper we have developed a new low-priced electrogalvanized steel sheet, which has a black resin
composite layer, to substitute conventional high-priced PCM steel and plastic mold for rear cover panel in the digital TV. The black resin composite was prepared by mechanical dispersion of the mixture solution that consists of high solid polyester resin, melamine hardener, black pigment, micronized silica paste, polyacrylate
texturing particle and miscellaneous additives. The composite solution was coated on the steel sheet using roll coater followed by induction furnace curing and cooling. Although the coated layer has a half thickness compared to the conventional PCM steels having 23㎛ thickness, it exhibits excellent quality for the usage of rear cover panel. The new steel sheet was applied to test products to get quality certification from worldwide electronic appliance customers. Detailed discussion provides in this paper including preparation of composite solution, roll coating technology, induction curing technology and quality evaluation from customers. - KEYWORDs : Digital TV, Composite, PCM steel, Plastic, Black Resin Coated Steel
- AUTHORs : Du-Hwan Jo†, Moonjae Kwon, Jae-Hwa Lee, Hee-Seung Kang, Yong-Gyun Jung, Yon-Kyun Song, Min-Hwan Jung, Soo-Hyoun Cho, Yeong-Bong Cho, Myoung-Rae Cho, Byoung-Chon Cho, Kwangsoo Lim, Pan-Woo Seon, Hyeon-Soop Han, Hwon-Woo Jeong, Jae-Ryung Lee, and Jong-Sang Kim
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Page : 7 - 11
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- 터보불로워 용 회전체 주축 소재의 마찰, 마모 및 부식 저항 향상을 위한 WC-metal 분말의 초고속화염용사코팅
- High velocity oxy-fuel (HVOF) spray coating of WC-metal powder (powder) was carried out to improve the resistances of friction, wear and corrosion of magnetic bearing shaft material Inconel718 (In718) of turbo blower. A micron sized WC-metal powder (86.5% WC, 9.5% Co 4% Cr) was coated onto In718 surface using HVOF thermal spraying. During the spraying, the binder metals and alloy such as Co, Cr
and Co-Cr alloy were molten and a small portion of WC particles were partially decomposed to W2C and free carbon at above its decomposition temperature of 1250ºC. The free carbon and excessively sprayed oxygen formed carbon oxide gases, resulting a porous coating of porosity of 2.2±0.3%. The surface hardness
of substrate increased approximately three times from 400 Hv of In718 to 1260±30 Hv of the coating The friction coefficients of the coating were approximately 0.33 ± 0.03 at 25ºC and 0.26 ± 0.03 at 450ºC. These values were smaller than those of In718 substrate at both temperatures due to the lubrication from the free carbon and the cobalt oxide debris. The corrosion resistance of the coating was higher than that
of In718 both in salt water of 3.5% NaCl and acid of 1 M HCl solutions, on the contrary, it was lower in base solution of 1 M NaOH. According to this study, the HVOF WC-metal powder coating is recommended for the durability improvement of magnetic bearing shaft of turbo blower. - KEYWORDs : Coating, friction, wear, corrosion
- AUTHORs : 주윤곤, 윤재홍, 조동율, 천희곤†
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Page : 12 - 26
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- 탄소강 볼트 체결된 GECM(Graphite Epoxy Composite Material)/Al 판재 간의 갈바닉 부식 거동
- This work focused on galvanic corrosion of carbon steel bolted GECM/Al plates by long-term test in tap water and NaCl solutions. Test product was carbon steel bolted between cross packed GECM and painted aluminium. Tests for the product and coupled parts determined corrosion rate in tap water and NaCl solutions. Also, using
a potentiostat and salt water sprayer, galvanic test was done. In galvanic test on carbon steel bolted GECM/Al plates, corrosion of carbon steel bolt was faster in series of tap water>1% NaCl solution>3.5% NaCl solution. In galvanic couple between aluminium and carbon steel bolt, their corrosion rates were higher than those of single specimen. In galvanic couple between GECM, aluminium, and carbon steel bolt, corrosion behaviors of carbon steel bolt and aluminium were changed due to different corrosion mechanism in tap water and chloride solution. - KEYWORDs : Galvanic corrosion, carbon steel bolted GECM, Al, tap water, NaCl
- AUTHORs : 김영식†, 박수진, 유영란
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Page : 27 - 33
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- 합금도금강판 내식성 향상을 위한 UV 경화형 유무기 하이브리드 코팅
- According to its merits about high curing speed and low emission of volatile organic compounds, UV curable inorganic-organic coating technology has been developed as an alternative for toxic and carcinogenic chromate- based treatments for years. It is consistently observed that ultra-thin films offer excellent corrosion protection as well as paint adhesion to metals. Based on the tetra-ethylorthosilicate(TEOS) and methacryloxypropyl trimethoxysilane(MPTMS), inorganic sol was synthesized and formed hybrid networks with UV curable acrylic monomer, 6-hexanediol diacrylate(HDDA), trimethylolpropane triacrylate(TMPTA), pentaerylthritol triacrylate(PETA). Several methods were used to test their properties such as salt spray test, potentiodynamic measurement, tape peel test, etc. It was shown that anti-corrosive property and stability of storage were affected by the molecular ratios of inorganic and organic compounds. It was not only the stability of storage, but had a excellent anti-corrosive, paint adhesive, and anti-solvent properties in a final molar ratios of 0.6/0.04/0.86/0.005 (TEOS/MPTMS/Acetone/HNO3) and 0.08/0.106/0.081/0.02 (TMPTA/HDDA/PETA/photo initiator).
- KEYWORDs : UV curable, hybrid coating, anti-corrosive, temporary corrosion protection, alloy plating coated
- AUTHORs : 박종원†·이경황·나현주·박병규·남영섭·홍신협
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Page : 34 - 39
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- NaCl 용액에서 Nb 첨가가 Ti 합금의 부식 거동에 미치는 영향
- In this study, the effect of niobium addition on the passivation behavior of Ti alloys in NaCl solution was investigated using various electrochemical methods. An α-phase in Ti alloy was transformed into a β-phase and martensite structure decreased as Nb content increased. The corrosion and passivation current density(+300 mVSCE) decreased as Nb content increased, and thereby a stable passive film was formed
on the Ti alloy. Potential of Ti-xNb alloy in the passive region increased, whereas, current density decreased with time from results of potentiostatic and galvanostatic tests. Also, the corrosion morphology showed the smaller pits as Nb content increased. Consequently, Ti alloy contained high Nb content showed a good resistance to pitting corrosion in 0.9 % NaCl solution. - KEYWORDs : Ti-xNb alloy, passivation, potentiostatic, galvanostatic, corrosion morphology
- AUTHORs : 김은실·김원기·최한철†
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Page : 40 - 49
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- Fe와 galvanic couple된 알루미늄의 내식성에 미치는 마그네슘의 영향
- Effects of magnesium and pH on corrosion of aluminum galvanically coupled to iron have studied by using potentio- dynamic and static tests for polarization curves, Mott-Schottky test for analysis of semiconductor property, and GD-AES and XPS for film analysis. Pitting potential was sensitive to magnesium as an alloying element but not to pH, while passive current was sensitive to pH but not to magnesium. It was explained with, instead of point defect model (PDM), surface charge model describing that the ingression of chloride depends on the state of surface charge and passive film at film/solution interface is affected by pH. In addition, galvanic current of aluminum electrically coupled to iron was not affected by magnesium in pH
8.4, 0.2M citrate solution but was increased by magnesium at the solution of pH 9.1. The galvanic current at pH 9.1 increased with time at the initial stage and after the exposure of about 200 minute, decreased and stabilized. The behavior of the galvanic current was related with the concentration of magnesium at the surface. It agreed with the depletion of magnesium at the oxide surface by using glow discharge atomic emission spectroscopy (GD-AES). In addition, pitting potential of pure aluminum was reduced in neutral pH solution where chloride ion maybe are competitively adsorbed on pure aluminum. It was confirmed by the exponential decrease of pitting potential with log of [Cl-] around 0.025 M of [Cl-] and linear decrease of the pitting potential. From the above results, unlike magnesium, alloying elements with higher electron negativity, lowering isoelectric point (ISE), are recommended to be added to improve pitting corrosion resistance of aluminum and its alloys in neutral solutions as well as their galvanic corrosion resistance in weakly
basic solutions. - KEYWORDs : Al-Mg alloys, galvanic corrosion, glow discharge atomic emission spectroscopy, high field model,
- AUTHORs : 현영민·김희산†
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