한국부식방식학회

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적층가공 (3D 프린팅) Ti-6Al-4V합금의 국부부식 저항성 평가를 위한 임계국부부식온도와 임계국부부식전위 측정방법의 비교
Additively manufactured (AM) Ti-6Al-4V alloys exhibit a dominant acicular martensite phase (α\\\'), which is characterized by an unstable energy state and highly localized corrosion susceptibility. Electrochemical critical localized corrosion temperature (E-CLCT, ISO 22910: 2020) and electrochemical critical localized corrosion potential (E-CLCP, ISO AWI 4631: 2021) were measured to analyze the localized corrosion resistance of the AM Ti-6Al-4V alloy. Although E-CLCP was measured under mild corrosive conditions such as human body, the validity of evaluating localized corrosion resistance of AM titanium alloys was demonstrated by comparison with E-CLCT. However, the mechanisms of resistance to localized corrosion on the as-received and heat-treated AM Ti-6Al-4V alloys under E-CLCT and E-CLCP differ at various temperatures because of differences in properties under localized corrosion and repassivation. The E-CLCT is mainly measured for initiation of localized corrosion on the AM titanium alloys based on temperature, whereas the E-CLCP yields repassivation potential of re-generated passive films of AM titanium alloys after breaking down.
KEYWORDs : Ti-6Al-4V, Additive manufacturing, E-CLCT, E-CLCP, Repassivation
AUTHORs : 서동일 ･ 이재봉†

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Ultrasonic Cavitation Behavior and its Degradation Mechanism of Epoxy Coatings in 3.5 % NaCl at 15 oC
Pipes operating in the seawater environment faces cavitation degradation and corrosion of the metallic component,as well as a negative synergistic effect. Cavitation degradation shows the mechanism by which materials deteriorate by causing rapid change of pressure or high-frequency vibration in the solution, and introducing the formation and explosion of bubbles. In order to rate the cavitation resistance of materials, constant conditions have been used. However, while a dynamic cavitation condition can be generated in a real system, there has been little reported on the effect of ultrasonic amplitude on the cavitation resistance and mechanism of composites. In this work, 3 kinds of epoxy coatings were used, and the cavitation resistance of the epoxy coatings was evaluated in 3.5% NaCl at 15 oC using an indirect ultrasonic cavitation method. Eleven kinds of mechanical properties were obtained, namely compressive strength, flexural strength and modulus, tensile
strength and elongation, Shore D hardness, water absorptivity, impact test, wear test for coating only and pull-off strength for epoxy coating/carbon steel or epoxy coating/rubber/carbon steel. The cavitation erosion mechanism of epoxy coatings was discussed on the basis of the mechanical properties and the effect of ultrasonic amplitude on the degradation of coatings.
KEYWORDs : Ultrasonic Cavitation test, Amplitude, Epoxy coating, 3.5% NaCl
AUTHORs : I. J. Jang, J. M. Jeon, K. T. Kim, Y. R. Yoo, and Y. S. Kim†

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Factors Affecting Stress Corrosion Cracking Susceptibility of Alloy 600 MA Steam Generator Tubes
In the past, Alloy 600 nickel-based alloys have been widely used in steam generators. However, most of them have been replaced by thermally treated alloy 690 tubes in recent years because mill annealed alloy 600 materials are known to be susceptible to stress corrosion cracking. Unlike this general perception, some
steam generators using mill annealed alloy 600 tubes show excellent performance even though they are designed, manufactured, and operated in the same way. Therefore, various analyses were carried out to determine causes for the degradation of steam generators. Based on the general stress corrosion cracking
mechanism, tube material susceptibility, residual stress, and sludge deposits of steam generators were compared to identify factors affecting stress corrosion cracking. It was found that mill annealed alloy 600 steam generator tubes showed higher resistance to stress corrosion cracking when the amount of sludge deposits on tube surface was smaller and residual stress generated during the fabrication was lower.
KEYWORDs : Stress corrosion cracking, Alloy 600 mill annealed tubes, Residual stress, Sludge deposits,Steam generator
AUTHORs : Kang Yong Seok†, Lee Kuk Hee, and Shin Dong Man

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Using Coffee-Derived Hard Carbon as a Cost-Effective and Eco-Friendly Anode Material for Li-Ion Batteries
Through a simple filtration process, followed by carbonization within a reductive environment, coffee waste grounds can be transformed into a non-porous hard carbon for use in multiple contexts. This resulting coffee-waste carbon has been evaluated as an eco-friendly and cost-effective replacement for conventional graphite. When compared with different types of carbon, our study found that the coffee-waste carbon fell into the category of hard carbon, as verified from the galvanostatic charge/discharge profiles. The coffee-waste carbon showed a superior rate capability when compared to that of graphite, while compromising smaller capacity at low C rates. During electrochemical reactions, it was also found that the coffee-waste carbon is well exposed to electrolytes, and its disordered characteristic is advantageous for ionic transport which leads to the low tortuosity of Li ions. Finally, the high irreversible capacity (low initial Coulombic efficiency) of the coffee-waste carbon, which if also often observed in amorphous carbon, can be adequately resolved through a solution-based prelithiation process, thereby proving that the coffee-waste carbon material is quite suitable for commercial use as an anode material for quickly-chargeable electrodes.
KEYWORDs : Coffee waste, Hard carbon, High-rate anodes, Li-ion batteries
AUTHORs : Sung Joo Hong, Seong Su Kim, and Seunghoon Nam†

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Anti-Corrosion Performance and Applications of PosMAC® Steel
PosMAC® is a brand of Zn-Mg-Al hot-dip coated steel sheet developed by POSCO. PosMAC® can form dense surface oxides in corrosive environments, providing advanced corrosion resistance compared to traditional Zn coatings such as GI and GA. PosMAC® 3.0 is available for construction and solar energy systems in severe outdoor environments. PosMAC®1.5 has better surface quality. It is suitable for automotive and home appliances. Compared to GI and GA, PosMAC® shows significantly less weight reduction due to corrosion, even with a lower coating thickness. Thin coating of PosMAC® provides advanced quality and productivity in arc welding applications due to its less generation of Zn fume and spatters. In repeated friction tests, PosMAC® showed lower surface friction coefficient than conventional coatings such as GA, GI, and lubricant film coated GA. Industrial demand for PosMAC® steel is expected to increase in the near future due to benefits of anti-corrosion and robust application performance of PosMAC® steel.
KEYWORDs : Anti-corrosion, Zn-Mg-Al alloy coating, PosMAC®1.5, PosMAC®3.0
AUTHORs : Il-Ryoung Sohn†, Tae-Chul Kim, Gwang-Il Ju, Myung-Soo Kim, and Jong-Sang Kim

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Cause Analysis for a Lining Damage in Sea Water System Piping Installed in a Korean Industrial Plant
Many Korean industrial plants including nuclear and fossil power plants use seawater as the ultimate heat sink to cool the heat generated by various facilities. Owing to the high corrosivity of seawater, facilities and piping made of metal material in contact with seawater are coated or lined with polymeric materials to avoid direct contact with seawater. However, polymeric materials used as coating and lining have some level of permeability to water and are degraded over time. Korean industrial plants have also experienced a gradual increase in the frequency of damage to pipes in seawater systems due to prolonged operating periods. In the event of a cavitation-like phenomenon, coating or lining inside the piping is likely to be damaged faster than expected. In this paper, the cause of water leakage due to base metal damage caused by the failure of the polyester lining in seawater system piping was assessed and the experience with establishing countermeasures to prevent such damage was described.
KEYWORDs : Lining, Coating, Seawater piping, Cavitation, Computational fluid dynamics
AUTHORs : K. M. Hwang† and S. K. Park

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