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Page : 78 - 83
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- BIW 전착도장에서의 컴퓨터 시뮬레이션 적용사례
- The e-coating to inhibit induced corrosion can deposit a coating not only on the exterior surface but also on the inside of whole metallic components of body-in-white (BIW). But it is difficult to deposit paint films on the inside area because metallic components are multi layered. It may cause shortness of e-coating
thickness. The only way to properly verify e-coating thickness is by performing the use of tear-down prototypes. When paint films’ thickness is inadequate, a structural modification on each metallic component is needed. Verification of the thickness improvement for a structural modification requires much manual effort and leads to increasing development time. Recently, the simulation technology has been developed to predict the e-coating thickness in e-coating field. By applying the simulation to BIW, improvement in paint thickness quality and shortening of development period are expected. The paper explains a validated solution that
allows simulating the effect of design changes to the e-coating thickness and current density, thereby delivering results within a time frame of a few days. - KEYWORDs : e-coating, electrochemical process, e-coating simulation, tear-down prototypes, paint bath characterization
- AUTHORs : 손대홍† · 정희진 · 안승호 · 김병수 · 김정연 · 최병삼
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Page : 84 - 91
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- 고온화학세정환경에서 20 % EDTA 용액이 결함 전열관 (Alloy600)에 미치는 영향
- The transport and deposition of corrosion products in pressurized water nuclear reactor (PWR) steam generators have led to corrosion (SCC, denting etc.) problems. Lancing, mechanical cleaning and chemical cleaning have been used to reduce these problems. The methods of lancing and mechanical cleaning have limitations
in removing corrosion products due to the structure of steam generator tubes. But high temperature chemical cleaning (HTCC) with EDTA is the most effective method to remove corrosion products regardless of the structure. However, EDTA in chemical cleaning aqueous solution and chemical cleaning environments affects
the integrity of materials used in steam generators. The nuclear power plants have to perform the pre-test (also called as qualification test (QT)) that confirms the effect on the integrity of materials after HTCC. This is one of the series studies that assess the effect, and this study determines the effects of 20 % EDTA aqueous solution on defective tubes in high temperature chemical cleaning environments. The depth and
magnitude of defects in steam generator (SG) tubes were measured by eddy current test (ECT) signals. Surface analysis and magnitude of defects were performed by using SEM/EDS. Corrosion rate was assessed by weight loss of specimens. The ECT signals (potential and depth %) of defective tubes increased marginally. But the lengths of defects, oxides on the surface and weights of specimens did not change. The average corrosion rate of standard corrosion specimens was negligible. But the surfaces on specimens showed traces of etching. The depth of etching showed a range on the nanometer. After comprehensive evaluation of all the results, it is concluded that 20 % EDTA aqueous solution in high temperature chemical cleaning
environments does not have a negative effect on defective tubes. - KEYWORDs : steam generator, high temperature chemical cleaning, EDTA, defective tubes, qualification test, ECT
- AUTHORs : 권혁철†
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Page : 92 - 107
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- 하이드라진으로 환원시킨 그래핀을 코팅한 오스테나이트와 마르텐사이트 스테인리스 강 고체고분자형 연료전지 금속 분리판의 전기화학적 특성 평가
- Graphene was coated on austenitic and martensitic stainless steels to simulate the metallic bipolar plate of proton exchange membrane fuel cell (PEMFC). Graphene oxide (GO) was synthesized and was reduced to reduced graphene oxide (rGO) via a hydrazine process. rGO was confirmed by FE-SEM, Raman spectroscopy
and XPS. Interfacial contact resistance (ICR) between the bipolar plate and the gas diffusion layer (GDL) was measured to confirm the electrical conductivity. Both ICR and corrosion current density decreased on graphene coated stainless steels. Corrosion resistance was also improved with immersion time in cathodic
environments and satisfied the criteria of the Department of Energy (DOE), USA. The total concentrations of metal ions dissolved from graphene coated stainless steels were reduced. Furthermore hydrophobicity was improved by increasing the contact angle. - KEYWORDs : PEMFC, bipolar plate, graphene, stainless steel, interfacial contact resistance, corrosion resistance
- AUTHORs : 차성윤 · 이재봉†
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Page : 153 - 158
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- Precursor Events in Environmentally Assisted Cracking Behaviour of Light Metals
- Light metal alloys of Mg, Ti, and Al undergo environmentally assisted cracking (EAC). Passive film breakdown and pitting are not only precursor events for stress corrosion, but can accelerate hydrogen evolution that is responsible for hydrogen embrittlement. This is clearly demonstrated in the case of Mg and Ti alloys. The so-called innocuous precipitates, which do not directly participate in either alloy strengthening or EAC
can be effective precursors for initiating EAC. This aspect is highlighted using high strength aluminium alloys. Such behaviours lead to a paradigm shift in the design of alloys with resistance to EAC. - KEYWORDs : environmentally assisted cracking, aluminium alloys, titanium alloys and magnesium alloys
- AUTHORs : V. S. Raja†
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Page : 113 - 119
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- Nuclear Corrosion: Achievements and Challenges
- Corrosion science faces new challenges in various nuclear environments. Three main areas may be identified where increases of knowledge and understanding have been done and are still needed to face the technical needs: (i) the extension of the service time of nuclear power plants from 40 years, as initially planned,
to 60 years and probably more as expected now, (ii) the prediction of long term behaviour of metallic materials in nuclear waste disposal where the corrosion processes have to be predicted over large periods of time, some thousands years and more, (iii) the choice of materials for use at very high temperatures as expected in Generation IV power plants in environments like gas (helium), supercritical water, liquid metals or salts. Service time extension, deep geological waste repositories and high temperature reactors sustain researches and developments to model corrosion phenomena at various scales, from atoms to components. - KEYWORDs : corrosion, generation 4, nuclear energy, nuclear power plant, nuclear waste disposal
- AUTHORs : Damien F?ron†
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Page : 120 - 124
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- Role of Ca in Modifying Corrosion Resistance and Bioactivity of Plasma Anodized AM60 Magnesium Alloys
- The effect of alloying element Ca (0, 1, and 2 wt%) on corrosion resistance and bioactivity of the as-received and anodized surface of rolled plate AM60 alloys was investigated. A plasma electrolytic oxidation (PEO) was carried out to form anodic oxide film in 0.5 mol dm-3 Na3PO4 solution. The corrosion behavior was studied by polarization measurements while the in vitro bioactivity was tested by soaking the specimens in Simulated Body Fluid (1.5xSBF). Optical micrograph and elemental analysis of the substrate surfaces indicated that the number of intermetallic particles increased with Ca content in the alloys owing to the formation of a new phase Al2Ca. The corrosion resistance of AM60 specimens improved only slightly by
alloying with 2 wt% Ca which was attributed to the reticular distribution of Al2Ca phase existed in the alloy that might became barrier for corrosion propagation across grain boundaries. Corrosion resistance of the three alloys was significantly improved by coating the substrates with anodic oxide film formed by PEO. The film mainly composed of magnesium phosphate with thickness in the range 30 - 40 μm. The heat resistant phase of Al2Ca was believed to retard the plasma discharge during anodization and, hence, decreased the film thickness of Ca-containing alloys. The highest apatite forming ability in 1.5xSBF was observed for AM60-1Ca specimens (both substrate and anodized) that exhibited more degradation than the
other two alloys as indicated by surface observation. The increase of surface roughness and the degree of supersaturation of 1.5xSBF due to dissolution of Mg ions from the substrate surface or the release of film compounds from the anodized surface are important factors to enhance deposition of Ca-P compound on the specimen surfaces. - KEYWORDs : magnesium, biodegradable, bioactivity, anodization, corrosion
- AUTHORs : Anawati Anawati, Hidetaka Asoh, and Sachiko Ono†
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Page : 125 - 128
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- High-Temperature Corrosion of T92 Steel in N2/H2O/H2S-Mixed Gas
- The ASTM T92 steel was corroded at 600 oC and 800 oC at 1 atm of N2/3.1%H2O/2.42%H2S-mixed gas. The formed scales were thick and fragile. They consisted primarily of the outer FeS scale and the inner (FeS, FeCr2S4)-mixed scale containing a small amount of the Cr2O3 scale. This indicated that corrosion occurred mainly via sulfidation rather than oxidation due to the H2S gas. Since FeS was present throughout the whole scale, T92 steel was non-protective, displaying high corrosion rates.
- KEYWORDs : Fe-Cr alloys, corrosion, sulfidation, H2S
- AUTHORs : Yuke Shi, Min Jung Kim, Soon Yong Park, M. Ali Abro, Poonam Yadav, and Dong Bok Lee†
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Page : 129 - 134
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- Ni 기지 초내열합금의 고온산화 저항성에 미치는 Ti의 영향
- The effects of Ti on the high temperature oxidation of Ni-based superalloys were investigated by cyclic oxidation at 850 °C and 1000 °C. The oxide scale formed at 850 °C consists of Cr2O3, Al2O3, and NiCr2O4 layers, while a continuous Al2O3 layer was formed at 1000 °C. The oxidation rate of the alloy with higher Ti content was higher than the alloy with less Ti content at 850 °C, possibly due to the increase in the metal vacancy concentration in the Cr2O3 layer involved by incorporation of Ti4+. However, Ti improved the oxidation resistance of the superalloy at 1000 °C by reducing oxygen vacancy concentration in Al2O3 layer.
- KEYWORDs : Ni-based superalloys, high temperature oxidation, thermal cycling, alloying element
- AUTHORs : 박시준·서성문·유영수·정희원·장희진†
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Page : 135 - 140
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- 원전 2차계통의 출력증강 운전에 따른 배관감육 영향 분석
- Piping and equipment are degraded by flow-accelerated corrosion (FAC) in nuclear power plants. FAC causes numerous problems and nuclear utilities maintain programs to control FAC. The key parameters influencing FAC are hydrodynamic conditions, water chemistry, and effect of materials. Recently, a nuclear utility has planned slight power uprates in Korea. Operating conditions need to be changed in the secondary system according to power uprates. This study analyzed the effect of wall-thinning caused by power uprates. The change of operation data in the secondary cycle is reviewed, and wall-thinning rates are analyzed in the main lines. As a result, two phase (mixture of water and steam) lines have a greater impact than a water line under power uprate conditions. Also, the quality of steam is the most important factor for FAC in two phase lines.
- KEYWORDs : flow-accelerated corrosion, wall-thinning, power uprates
- AUTHORs : 윤훈·황경모·이효승·문승재†
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Page : 141 - 146
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- Ni-Cr과 Co-Cr 합금을 이용한 치과보철물의 부식 특성 및 도재 접합성
- By using Ni-Cr and Co-Cr alloys, porcelain fused to metal (PFM) samples were prepared to examine the interface and the surface corrosion behavior. The potentiodynamic polarization analysis showed that the corrosion current density of Co-Cr alloy (1.61×10-6A/㎠) was three times lower than that of Ni-Cr alloy
(4.83×10-6A/㎠) at room temperature. A dental prosthesis consisting of the porcelain fused to Ni-Cr alloy extracted from a patient after approximately four years of usage was examined to assess its resistance to corrosion. OM and SEM images of the metal part revealed a typical pitting corrosion. As compared to porcelain fused to Ni-Cr alloy having a thick layer (~10 ㎛) of oxide at the interface, a relatively thin
oxide layer (less than 5 ㎛) was formed on Co-Cr alloy, indicating that the interface between Co-Cr alloy and porcelain may have a better adhesion strength than the interface between Ni-Cr alloy and porcelain. - KEYWORDs : dental prosthesis, porcelain fused to metal (PFM), pitting corrosion, Ni-Cr, Co-Cr
- AUTHORs : 김기정·최병기·오두록·최병상†
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