• Corrosion Science and Technology
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• 제14권4호
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• pp.161-165
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• 2015

This paper presents an analysis of thermal stress induced along the interface between a polymeric coating layer and a steel substrate as a result of uniform temperature change. The epoxy layer is assumed to be a linear viscoelastic material and to be theromorheologically simple. The viscoelastic boundary element method is employed to investigate the behavior of interface stresses. The numerical results exhibit relaxation of interface stresses and large stress gradients, which are observed in the vicinity of the free surface. Since the exceedingly large stresses cannot be borne by the polymeric coating layer, local cracking or delamination can occur at the interface corner.

• Ocean Systems Engineering
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• 제3권1호
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• pp.1-8
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• 2013

This brief study aims at providing a model to predict the time of service of a cracked bar in corrosive environment, in view of both the fracture mechanics and elastic failure criteria. Dolinskii's assumption on the relationship between stress and the corrosion rate is adopted. It is superimposed with fracture mechanics consideration. A comparison between the time of service of a cracked bar and that of a uniform bar is provided.

• 한국표면공학회지
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• 제27권2호
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• pp.74-82
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• 1994

The structure and properties such as adhesion and corrosion resistance of Cr and $Cr_2O_3$ films, deposited on steel plates by the vacuum evaporation method, were investigated. According to the ESCA and AES analy-sis, it could be concluded that chromium oxide with uniform composition could be formed on the steel sub-strate. The deposited Cr and $Cr_2O_3$ films had high adhesion strength, and they did not peeled off by the tape test. The adhesion property, however, was deteriorated as the film thciknes increased. After bending of the deposited specimen many cracks were observed by SEM, and they were assumed to have propagated along co-lumnar boundaries by the bending test. The corrosion resistance of the films was not generally good, which in-dicates that the films had a porous structure with a large number of defects such as pin holes and voids.

• 동력기계공학회지
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• 제5권3호
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• pp.88-94
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• 2001

Stellite 12 alloy-powders were overlaid on 410 stainless steel valve seat using plasma transferred arc(PTA) process. Variation of the microstructure, hardness, wear and corrosion of overlaid deposit with current change was investigated. The deposit showed hypoeutectic microstructure, which was consisted of primary cobalt dendrite and networked $M_7C_3$ type eutectic carbides. As current increased, the amount of eutectic carbide decreased and its dendritic secondary arm spacing increased. Hardness of the deposit was decreased with increase of current. Stress relief heat treatment at $600^{\circ}C$ for two hours resulted in slight increase of hardness in the deposit and showed uniform hardness distribution in base metal without any hardened layer in HAZ. Specific wear decreased with increase of sliding distance. The deposit of high hardness with a lot of eutectic carbide showed relatively low specific wear. Initial corrosion current density of the deposit in 0.1N sulfuric acid was lower than those of 410 stainless steel, and showed a little variation with PTA current.

• 한국표면공학회지
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• 제49권1호
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• pp.62-68
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• 2016

A chromium-free Ce-based conversion coating formed by immersion in a solution containing cerium chloride and nitric acid on AZ31 magnesium alloy has been studied. The effects of acid pickling on the morphology and the corrosion resistance of the cerium conversion coating were investigated. The corrosion resistance of the conversion coating prepared on AZ31 Mg alloy after organic acid pickling was better than that of inorganic acid pickling. The morphology of the conversion-coated layer was observed using optical microscope and SEM. Results show that the conversion coatings are relatively uniform and continuous, with thickness 1.0 to $1.1{\mu}m$. The main elements of the conversion coating of AZ31 Mg alloy are Mg, O, Al, Ce and Zn by EDS analysis. The electrochemical polarization results showed that the Ce-based conversion coating could reduce the corrosion activity of the AZ31 Mg alloy substrates in the presence of chloride ions.

• Journal of Advanced Marine Engineering and Technology
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• 제30권1호
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• pp.157-168
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• 2006

Recently, interest in using Al alloys in ship construction instead of fiber-reinforced plastic (FRP) has increased because of the advantages of A) alloy ships over FRP ships, including high speed, increased load capacity. and ease of recycling. This paper investigated the mechanical and electrochemical properties of Al alloys in a slow strain rate test under various potential conditions. These results will provide reference data for ship design by determining the optimum protection potential regarding hydrogen embrittlement and stress corrosion cracking. In general, Al and Al alloys do not corrode on formation of a film that has resistance to corrosion in neutral solutions. In seawater, however, $Cl^-$ ions lead to the formation and destruction of a Passive film. In a potentiostatic experiment. the current density after 1200 sec in the Potential range of $-0.68\~-1.5\;V$ was low. This low current density indicates the protection potential range. Elongation at an applied potential of 0 V was high in this SSRT. However, corrosion protection under these conditions is impossible because the mechanical properties are worse owing to decreased strength resulting from the active dissolution reaction in parallel parts of the specimen. A film composed of $CaCO_3\;and\;Mg(OH)_2$ confers corrosion resistance. However, at potentials below -1.6 V forms non-uniform electrodeposition coating, since there is too little time to form a coating. Therefore, we concluded that the mechanical properties are poor because the effect of hydrogen gas generation exceeds that of electrodeposition. Comparison of the maximum tensile strength, elongation, and time to fracture indicated that the optimum protection potential range was from -1.45 to -0.9 V (SSCE).

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.149-149
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• 2017

Aluminum alloys have poor corrosion resistance compared to the pure aluminum due to the additive elements. Thus, anodizing technology artificially generating thick oxide films are widely applied nowadays in order to improve corrosion resistance. Anodizing is one of the surface modification techniques, which is commercially applicable to a large surface at a low price. However, most studies up to now have focused on its commercialization with hardly any research on the assessment and improvement of the physical characteristics of the anodized films. Therefore, this study aims to select the optimum temperature of sulfuric electrolyte to perform excellent corrosion resistance in the harsh marine environment through electrochemical experiment in the seawater upon generating porous films by variating the temperatures of sulfuric electrolyte. To fabricate uniform porous film of 5083 aluminum alloy, we conducted electro-polishing under the 25 V at $5^{\circ}C$ condition for three minutes using mixed solution of ethanol (95 %) and perchloric (70 %) acid with volume ratio of 4:1. Afterward, the first step surface modification was performed using sulfuric acid as an electrolyte where the electrolyte concentration was maintained at 10 vol.% by using a jacketed beaker. For anode, 5083 aluminum alloy with thickness of 5 mm and size of $2cm{\times}2cm$ was used, while platinum electrode was used for cathode. The distance between the two was maintained at 3 cm. Anodic polarization test was performed at scan rate of 2 mV/s up to +3.0 V vs open circuit potential in natural seawater. Surface morphology was compared using 3D analysis microscope to observe the damage behavior. As a result, the case of surface modification showed a significantly lower corrosion current density than that without modification, indicating excellent corrosion resistance.

• Corrosion Science and Technology
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• 제7권6호
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• pp.319-323
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• 2008

The polarization resistance of mild steel in 0.5M hydrochloric acid has been evaluated by using impedance (Z) and linear polarization (LPR) techniques and compared to the noise resistance obtained from electrochemical noise data. The degree of localization of this general corrosion has also been discussed by evaluating localization index and power spectral density. Polarization resistance obtained by LPR technique ($28\Omega$) was higher than that obtained by impedance technique ($15\Omega$). Noise resistance ($11\Omega$) was much lower than polarization resistance measured by both of above techniques. Higher polarization resistance obtained by LPR technique is generally caused by passivation effect in the presence of scales or deposits which can introduce an increased resistance as can low conductivity electrolytes. The reason why noise resistance is lower than polarization resistance is the effect of background noise detected by using three platinum electrodes cell in 0.5M hydrochloric acid. Slope($-\beta$) of power spectral density (PSD) obtained from analysis of noise data ($-\beta$ = 3.3) was much higher than 2 which indicates mild steel corroded uniformly. Localization index (LI) calculated from statistical analysis (LI=0.08) is much lower than 1 which indicates that mild steel did not corroded locally. However, LI value is still higher than $1x10^{-3}$ and this indicates that mild steel corroded locally in microscopic point of view.

• 한국건축시공학회지
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• 제23권5호
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• pp.559-570
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• 2023

건설산업에서 사용되는 구조용 강재의 부식은 산업화로 인해 많은 공격적인 이온이 내포된 대기 환경에서 증가추세에 있다. 따라서 본 연구에서는 아크 및 플라즈마 아크용사로 Al 코팅을 용착하여 Cl^-와 CO₃^2-같은 공격적인 이온을 다량 함유한 Society of Automotive Engineering(SAE) J2334 용액의 모사대기환경에서 그 효과를 비교하였다. 다양한 분석기법으로 코팅 특성과 부식 메커니즘을 고찰하였다. 플라즈마 아크용사로 용착된 Al 코팅은 밀도 있고 균일하면 층층이 적층이 잘 되었고 높은 부착력이 나타났다. 이 공법으로 용착된 Al 코팅을 SAE J2334 용액에 기간별로 침지하여 측정한 개회로전위(OCP)는 아크용사로 용착된 Al 코팅보다 더 양전성(electropositive)한 값을 보여주었다. 플라즈마 아크용사는 총 임피던스가 아크용사보다 높게 나타났다. SAE J2334 용액에 23일 침지하였을 때 플라즈마 아크용사 Al 코팅의 부식속도는 아크용사에 비해 20% 감소하였다.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2004년도 학술논문집
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• pp.285-291
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• 2004

LiCl-$Li_2O-O_2$ 용융염계에서 용융염 취급장치의 구조재료를 위한 평가의 일환으로 Inconel 718, X-750, Haynes 75, 263 합금의 부식거동을 분위기온도; $650^{\circ}C$, 부식시간: 24~168h, $Li_2O$농도; 3wt%, 혼합가스농도; Ar-10%$O_2$에서 조사하였다. LiCl-$Li_2O-O_2$ 용융염계에서 부식속도는 Haynes 263 ＜ Haynes 75 ＜ Inconel X-750 ＜ Inconel 718 순서로 나타났으며, Haynes 263 합금이 가장 우수한 내부식성을 나타내었다. Haynes 75의 부식생성물은 $Cr_2O_4$, $NiFe_2O_4$, $LiNiO_2$, $Li_2NiFe_2O_4$, Inconel 718의 부식생성물은 $Cr_2O_4$ 및 $NiFe_2O_4$ 이며 Haynes 263은 $Li(Ni,Co)O_2$, $NiCr_2O_4$ 및 $LiTiO_2$, Inconel X-750은 $Cr_2O_3$, $NiFe_2O_4$,$FeNi_3$, (Al,Nb,Ti)$O_2$의 부식생성물을 나타내었다. Haynes 263은 국부부식의 거동을 보이는 반면, Haynes 75, Inconel 718 및 Inconel X-750은 전면 부식 거동을 나타내었다.