Papers by Keyword: Localized Corrosion

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Authors: Di Li, Guo Qiang Li, Bao Lan Guo, Ming Xia Peng
Authors: Azzura Ismail
Abstract: Austenitic stainless steels especially 316L has been used extensively in many sectors including construction, medical and household appliances due to their highly resistance to corrosion attack, reasonable cost and excel in mechanical properties. However, in corrosive media, 316L are susceptible to localised corrosion attack especially in seawater and high temperature. The corrosiveness of media increased as the anions contents increased. This paper presents the corrosion mechanism of 316L exposed to high concentration of sulphate in the salinity of seawater. The solution (media) was prepared according to the same composition as seawater including pH, salinity and dissolved oxygen. The corrosion mechanism were characterized to breakdown potential (Eb) of 316L which are the potential once reaches a sufficiently positive value and also known as pitting potential. This is the most point where localized corrosion susceptibility to evaluate and considered a potential, which could be an appropriate point according to any given combination of material/ambient/testing methods. The Eb value were identified at 4°C, 20°C, 50°C and 80°C and compared with Eb value of 316L in seawater. The Eb value of 316L in high sulphate are higher compared to seawater in every temperature which elucidate that some anions accelerate corrosion attack whereas some anions such as sulphate behaves as inhibiting effect to 316L.
Authors: Adriana Sorcoi, Raluca Fako, S. Cojocaru
Abstract: The paper aims to discuss some aspects on corrosion behavior of specimens from sintered CuNi alloys (e.g. Cu90Ni10; Cu70Ni30). The above mentioned specimens were manufactured by dissimilar laboratory routes: from alloyed powders, from elementary powders and from mixtures consisting of Cu80Ni20 alloy and an alloying element. Research aims to establish the manufacturing parameters influence on sintered specimens characteristics (density, porosity, microstructure features) in order to correlate them with corrosion tests laboratory data. There were investigated the corrosion mechanisms in relation with macro- and microstructure properties of the sintered specimen surface. For comparison purposes, it is intended to extend the analysis to Cu60Ni40 and Cu80Ni20 sintered alloys.
Authors: Kyung Man Moon, Sung Yul Lee, Jae Hyun Jeong, Myeong Hoon Lee
Abstract: The galvanized steel structures may be inevitably corroded rapidly in the case of exposed to corrosive environments for long time, and these corrosive environments has been accelerated with increasing the environmental contamination due to the rapid development of industrial society. However, since the galvanizing method have the various merits compared to surface coating treatment in economical point of view, the galvanized steel have been extensively used to the numerous constructional steels such as a guard rail of high way, various types of structural steel for manufacturing ship and various industrial fields etc.. Therefore, it has been made an effort to improve the corrosion resistance of the galvanizing film through various methods such as variation of chemical composition of galvanizing bath, chromate treatment and coating treatment etc.. In this study, comparison evaluation on the corrosion resistance of three types of the test specimens, that is, three samples of pure galvanizing, galvalume and chromate treatment were investigated using electrochemical methods in 1% NaOH solution. The samples of chromate treatment and of galvalume exhibited the lowest and highest corrosion current density respectively in 1% NaOH solution. In addition, the sample of chromate treatment revealed the highest impedance at 0.01Hz, which is considered that the oxide film by chromate treatment is deposited on the surface of pure galvanizing sample. After drawing polarization curves, the corroded surface of the pure galvanizing specimen indicated pattern like as localized corrosion, moreover, the large amount of corrosive products was observed on the surface of galvalume sample. However, the smooth pattern nearly similar to general corrosion was observed at the corroded surface of the sample of chromate treatment. Consequently, it is considered that the chromate treatment is an optimum method compared to pure galvanizing and, galvalume treatment to improve corrosion resistance in 1% NaOH solution.
Authors: Seung Chan Na, Seung Ho Park, Woon Suk Hwang
Abstract: In this study, a current density contour map of TiNi shape memory alloy in sodium sulfate solutions was constructed by potentiodynamic polarization technique. The current density contour map of TiNi alloy, constructed in a 0.5 M sodium sulfate solution over the pH range 1 to 13 at 37oC, showed only hydrogen evolution region, passive region, and oxygen evolution region. The localized corrosion region did not exist and the susceptibility of localized corrosion was not exhibited. We also investigated the effects of chloride ions on the pitting corrosion of TiNi alloy in sodium sulfate solutions. Pitting corrosion occurred with addition of 0.2 M NaCl in a sulfate solution. And it was observed that pitting potential got lower as the concentration of chloride ion went up. However, repassivation potential was not affected by the addition of chloride ion up to 0.5 M. It is concluded that a TiNi shape memory alloy exists as a passive state and a good corrosion resistance in sulfate solutions over the pH range 1 to 13, and the sulfate ion performs a role of inhibiting localized corrosion in chloride environment.
Authors: A. Burgueño, T. Dieguez, H. Svoboda
Abstract: Friction Stir Processing (FSP) is a variant of Friction Stir Welding, and can be used to modify the materials microstructure to functionalize it. Superplastic forming is a technological process used to produce components with very complex shapes. In the last two decades it has been a topic of major development. In Fine Structure Superplasticity (FSSP), the initial grain size exerts a strong influence on the superplastic strain rate and temperatures. Refining grain size (GS) the parameters (temperature and strain rate) of superplastic forming could be optimized. Thermal stability is also an important factor to obtain superplasticity. FSP is used to refine GS, but the optimum processing parameters are still under study over different materials. Corrosion resistance can be affected by FSP too, but the information about it is scarce. In the present study, 7075-T651 aluminium alloy was friction stir processed under different conditions in order to improve superplastic behavior. Tool profile, rotation rate and traverse speed were analyzed. Microstructures with <4 μm grain size were obtained. The maximum superplastic elongations, in a range of 740 to 900%, at 400°C were obtained at 1x10-2s-1 strain rate. The results were discussed in terms of constitutive equations and microstructure evolution. Localized corrosion potentials were obtained. Localized corrosion resistance was affected by friction stir processing.
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