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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†

Page : 135 - 140 DOWNLOAD
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†

Page : 129 - 134 DOWNLOAD
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†

Page : 125 - 128 DOWNLOAD
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†

Page : 120 - 124 DOWNLOAD
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†

Page : 113 - 119 DOWNLOAD
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 Féron†

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