Cyclic Potentiodynamic Polarization Technique Research Articles

Effect of Artificial Aging in the Microstructure and Corrosion Performance of Superduplex UNS S32750 Stainless Steel

Superduplex stainless steels have great mechanical and corrosion properties. However, its chemical composition makes it prone to intermetallic phase precipitation during thermal processing. Sigma (σ), chi (χ), and chromium nitrides (Cr2N) remove Cr and Mo from the matrix, reducing the corrosion and mechanical resistance. Understanding the effects of thermal processing on the secondary phase’s precipitation and depletion of the material’s performance is crucial to its applications. Thus, this work aims to analyze the behavior of the corrosion performance of the UNS S32750 after thermal treatment at 800°C, for 60, 180, 300, and 420 minutes, in comparison to the as-received material. Optical emission spectrometry, X-ray diffraction, and SEM with backscattered electrons (BSE) were used to evaluate the material. The corrosion performance was evaluated with the cyclic potentiodynamic polarization technique. The main results and conclusions obtained in the study were a decomposition of the ferrite phase into the χ and σ phases, with the formation of the χ phase being predominant in shorter times, while for longer aging times σ formed in greater quantities. It was also possible to verify a more aggressive corrosion trend for aged samples in the regions adjacent to the formation of the χ and σ phases. It was also possible to observe that the losses generated in corrosion resistance were greater for aging times longer than 60 minutes. The aging treatment significantly reduced the material’s corrosion resistance in conjunction with the formation of precipitates.

High performance aluminized Monel coatings with prolonged corrosion resistance in saline environment

This study compares the corrosion resistance of as-sprayed and aluminized Monel 400 coatings annealed at 900 °C, and deposited on sand-blasted stainless steel. The coatings were immersed in 3.5 wt % NaCl solutions and analyzed using electrochemical impedance spectroscopy and cyclic Potentiodynamic polarization techniques for up to 100 days. Microstructural analysis showed decreased porosity as well as oxide and aluminide layer formation in annealed Monel 400 coatings. Formation of aluminides enhances the Vicker's hardness up to 4 times as compared to as-sprayed coatings. The results showed that the annealed coatings, particularly the aluminide coatings, exhibited higher corrosion resistance than the as-sprayed coatings. Additionally, the corrosion rate decreased exponentially, and the polarization resistance increased significantly as the immersion time increased. This study provides insights into cost-effective Ni-based coatings for corrosion resistance applications.

High wear resistance and better pitting corrosion resistance of AISI 316L stainless steel by a self-protective oxy-nitrocarburizing paste

Simultaneous oxidation and nitrocarburizing of AISI 316 SS at 580 °C for 5, 10, 15, and 20 min were studied using self-protecting pastes of sodium cyanate and sodium carbonate. The analytical techniques of XRD and SEM/EDS allowed the characterization of surface modifications. The corrosion resistance was evaluated in a synthetic seawater solution using the cyclic potentiodynamic polarization technique. The cross-section hardness and wear resistance were assessed by Vickers indentation and pin-on-disc, respectively. This thermochemical process formed an oxidized compound layer above a solid nitrogen solution in austenite. The compound layer was composed of intermixed crystals of Fe3O4, ε-Fe3N, and expanded austenite. With increasing relative proportions of the first two phases and decreasing relative proportions of the third phase with increasing treatment time. The balance between the expanded austenite and the chemical composition of the compound layer improved the hardness, the wear-resistant, and the pitting corrosion resistance of the AISI 316L SS surface simultaneously. Oxy-nitrocarburizing at 580 °C for 10 min allowed the best-localized corrosion resistance. However, the sample oxy-nitrocarburized for 20 min reached a more stable passive zone with the highest wear resistance. Self-protective pastes based on sodium cyanates and carbonates allowed the oxy-nitrocarburizing process to consume less salt than the traditional molten salts.

Susceptibility to Pitting Corrosion of Ti-CP2, Ti-6Al-2Sn-4Zr-2Mo, and Ti-6Al-4V Alloys for Aeronautical Applications

Titanium alloys are used in different industries like biomedical, aerospace, aeronautic, chemical, and naval. Those industries have high requirements with few damage tolerances. Therefore, they are necessary to use materials that present fatigue, mechanical, and corrosion resistance. Although Ti-alloys are material with high performance, they are exposed to corrosion in marine and industrial environments. This research shows the corrosion behavior of three titanium alloys, specifically Ti CP2, Ti-6Al-2Sn-4Zr-2Mo, and Ti-6Al-4V. Alloys were exposed on two electrolytes to a 3.5 wt % H2SO4 and NaCl solutions at room temperature using cyclic potentiodynamic polarization (CPP) and electrochemical noise (EN) according to ASTM G61 and ASTM G199 standards. CPP technique was employed to obtain electrochemical parameters as the passivation range (PR), corrosion type, passive layer persistence, corrosion potential (Ecorr), and corrosion rate. EN was analyzed by power spectral density (PSD) in voltage. Results obtained revealed pseudopassivation in CPP and PSD exposed on NaCl for Ti-6Al-2Sn-4Zr-2Mo, indicating instability and corrosion rate lower. However, Ti-6Al-4V presented the highest corrosion rate in both electrolytes. Ti-6Al-2Sn-4Zr-2Mo revealed pseudopassivation in CPP and PSD in NaCl, indicating a passive layer unstable. However, the corrosion rate was lower in both solutions.

Interpretation of Cyclic Potentiodynamic Polarization Test Results for Study of Corrosion Behavior of Metals: A Review

The cyclic potentiodynamic polarization technique is a method for evaluating the susceptibility of a metal to localized corrosion such as pitting and crevice corrosion. This paper provides the information to conduct the cyclic polarization test correctly and to help performing the interpretation of the polarization scan properly. The effect of critical parameters including solution resistivity, scan rate, point of scan reversal, aggressive ions, corrosion inhibitors, metastable pits, metallurgical variables, temperature, dissolution gases, pH, immersion duration and surface roughness on the cyclic polarization curve and results interpretation are discussed. Then a number of cyclic potentiodynamic polarization curves for common metals and alloys in prevalent environments are given.

The impact of elevated lithium concentration 3.5 ppm on the corrosion rate of zirconium

Corrosion of zirconium in presence of LiOH was studied by cyclic potentiodynamic polarization technique. SEM was used to observe the visual appearance of oxide film after the procedure. The measurements were carried out at room temperature and open to air. Our investigations show the accelerated electrochemical corrosion is caused by 3.5 ppm rather than 2.2 ppm. The important observation is the steep decrease in corrosion rate at 2.2 ppm Li ion.

Crevice Corrosion of Duplex Stainless Steels by Cyclic Potentiodynamic Polarization and Potentiostatic Techniques

Crevice corrosions of duplex stainless steels were investigated under the aggressive condition of sea water pumps in offshore petroleum platforms. The study aims to compare crevice corrosion behavior of three grades of duplex stainless steels, UNS S32101 (2101), UNS S31803 (2205) and UNS S32750, in seawater with 200 ppm of hypochlorite. Duplex steels were compared with a widely used austenitic steel UNS S31603 (316). Specimens were tested under synthetic sea water prepared at pH4, pH6 and pH8 by the cyclic potentiodynamics polarization technique and the potentiostatic technique. The results show that the duplex stainless steels had higher corrosion resistance compared with the 316. The released charges and the corrosion rates of the 2101 and the 2205 were similar, but much lower than those of the 2507especially after 3 months period.

Preliminary Study on Dimocarpus Longan Peel as Inhibitors for the Pitting Corrosion of 5052-O and 6061-O Aluminium Alloys in Artificial Brine Solution

The effect of dimocarpus longan peel extract onthe pitting corrosion of 5052-O and 6061-O aluminiumalloys in an aqueous solution of artificial brine has beenstudied employing open circuit potential (OCP) and cyclicpotentiodynamic polarization techniques. Moreover, surfacestudies such as scanning electron microscope (SEM) andenergy dispersive spectroscopy (EDS) were also applied. Theaddition of that extract increases pitting potential (Epit) bothaluminium alloys, increasing the resistance of pittingcorrosion both them. On the other hand, the resistance ofpitting corrosion on 6061-O alloy was higher than that of5052-O alloy during the addition of that extract. Theaddition of that extract also shifts OCP towards to positivepotentials both alloys, which indicates the formation of apassive surface layer on the surface of alloys. On the basis ofresults, the appearance of pit shows on the surface of 5052-Oalloy due to the presence Fe-enrich phase, compared to thatof 6061-O alloy International Journal of Engineering Research,2017, Volume No.6, Issue No.1 0, pp : 433-436

Corrosion and Wear Resistance Characterization of Environmentally Friendly Sol–gel Hybrid Nanocomposite Coating on AA5083

Environmentally friendly organic–inorganic hybrid nanocomposite films have been developed by sol–gel method for corrosion protection of AA5083 alloy. The hybrid nanocomposite coatings have been synthesized from tetraethylorthosilicate (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) precursors. The multilayer coatings were prepared by dip-coating technique. Attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectroscopy was carried out to show the formation of the Si–O–Si structural backbone of the hybrid coatings. Structure and surface morphology of the coatings were studied by optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Characterization of the coatings with respect to pencil scratch hardness, adhesive and abrasion resistance was performed. The corrosion protection performance of these coatings was examined by using cyclic potentiodynamic polarization technique in Persian Gulf water. The results revealed that crack-free films with smooth surface were obtained. With increasing the number of sol–gel coated layers, corrosion resistance increased from 81 to 419 kΩ cm 2 , while the abrasion wear resistance did not change significantly. However, the triple sol–gel coated layer offered excellent protection against corrosion.

Corrosion Behavior of HRB400 Reinforcing Steel Using Cyclic Potentiodynamic Polarization Technique

HRB400 reinforcing steel due to high strength and high ductibility is as the main reinforcing steel in “Code for design of concrete structures (GB50010-2002)” in China. Cyclic potentiodynamic polarization technique was used to investigate the electrochemical corrosion bebavior of HRB400 reinforcing steel in Simulated Concrete Pore solutions (SCP solutions) differently contaminated by bicarbonate ions and/or chloride ions. The evolution feature of the corrosion parameters was analyzed and was compared with that of HPB235 reinforcing steel. The results show that the corrosion characteristics of HRB400 and HPB235 were exceedingly similar before the destruction of the passivation film. However, HRB400 is remarkedly more susceptible to chloride ions and carbonation than HPB235 during the failure of the passivation films. The pH threshold for HRB400 is larger than that for HPB235, and the chlorides threshold for the former is smaller than that of the latter. When HRB400 and HPB235 were connected and exposed to an aggressive environment, the galvanic corrosion will occur where HRB400 is anode and HPB235 is cathode. To ensure the durability of the reinforcing concrete structures, it is necessary to make the connection points insulate.

Determining the appropriate scan rate to perform cyclic polarization test on the steel bars in concrete

Abstract Cyclic potentiodynamic polarization technique is a relatively non-destructive measurement that can provide information about the corrosion rate, corrosion potential, susceptibility to pitting corrosion of the metal and concentration limitation of the electrolyte in the system. The technique is built on the idea that predictions of the behavior of a metal in an environment can be made by forcing the material from its steady state condition and monitoring how it responds to the force as the force is removed at a constant rate and the system is reversed to its steady state condition. Applied potential is the force and is raised at a continuous, often slow, rate by using potentiostat. This rate is called polarization scan rate and is an experimental parameter. It is very important to choose the most appropriate scan rate, specifically in the complicated system such as reinforced concrete; otherwise the result does not reflect the corrosion behavior and the result could be an incorrect polarization scan and an incorrect prediction from it. In this paper, the effect of different scan rates on the apparent corrosion behavior is shown and a method to choose the appropriate rate is discussed.

Measuring the Repassivation Potential of Alloy 22 Using the Potentiodynamic-Galvanostatic-Potentiostatic Method

Abstract Traditionally, the susceptibility of Alloy 22 (N06022) to suffer crevice corrosion has been measured using the Cyclic Potentiodynamic Polarization (CPP) technique (ASTM G 61). When the alloy is not very susceptible to crevice corrosion, the values of repassivation potential obtained using the CPP technique are not highly reproducible. To circumvent the large uncertainty in the values of the repassivation potential by the CPP method, the repassivation potential of Alloy 22 may be measured using a slower method that combines sequentially potentiodynamic, galvanostatic, and potentiostatic treatments (this method is called the Tsujikawa-Hisamatsu Electrochemical or THE method). In the THE method the anodic charge is applied to the specimen in a more controlled manner, which avoids driving the alloy to transpassivity and therefore results in more reproducible repassivation potential values. Results using THE method under various testing conditions are presented. A new standard has been prepared for ASTM balloting for the THE method. The round robin matrix results are also discussed.

Degradations of Type 422 stainless steel in aqueous environments

The susceptibility of Type 422 stainless steel (UNS S42200) to stress corrosion cracking (SCC) and localized corrosion was determined in neutral and acidic aqueous solutions at ambient and elevated temperatures. No failures were observed in the neutral solution at constant load. SCC testing by the slow-strain-rate technique revealed reduced ductility, time-to-failure and true failure stress due to the combined effect of elevated temperature and lower pH. These parameters were further reduced due to the cathodic charging. The localized corrosion studies using the cyclic potentiodynamic polarization technique showed pits and crevices in all specimens. Metallographic and fractographic evaluations showed secondary cracks along the gage section, and a combination of ductile and brittle failures at the primary fracture face of the tested specimen, respectively, depending upon the test environment.

Avaliação da resistência à corrosão em aço inoxidável martensítico do tipo Cr-Ni em meio marinho sintético simulando atividades em águas profundas

Esse trabalho estuda a resistência à corrosão do aço inoxidável martensítico fundido em meio marinho sintético saturado com CO2 e também faz uma comparação com solução aerada. A liga foi usada na condição temperada e revenida. A corrosão foi avaliada usando a técnica de polarização potenciodinâmica cíclica. As medidas de polarização foram obtidas em meio marinho sintético com concentrações de cloreto de 20000ppm e 80000ppm na temperatura ambiente. As curvas de polarização cíclica obtidas mostram uma região de passivação definida para as condições adotadas para o ensaio, sendo possível para a identificação dos parâmetros eletroquímicos, o potencial de pite, o potencial de proteção e a susceptibilidade ao pite. Em solução saturada com CO2 e concentração de cloreto de 20000ppm, o potencial de proteção aumentou e a susceptibilidade ao pite diminuiu, em comparação com a solução aerada. Em contraste, os potenciais de pite e de proteção decresceram em solução saturada com CO2 e concentração de cloreto de 80000ppm, indicando que a resistência ao pite é influenciada por um sinergismo entre a concentração de cloreto e a solução saturada com CO2.

Susceptibility of nitinol to localized corrosion

The effect of different conditions on the susceptibility of nitinol to localized corrosion was examined using the cyclic potentiodynamic polarization technique. Tests were performed on mechanically polished (MP) and electropolished (EP) nitinol wire in 0.9 wt % NaCl and phosphate-buffered saline (PBS). A polarization curve was also obtained for an EP stent in the NaCl. Differences between the breakdown potential and the corrosion potential (E(corr)) and between the protection potential and E(corr) were used to evaluate the susceptibility to pitting corrosion and crevice corrosion, respectively. The type of solution and, particularly, the surface condition affected the resistance of nitinol to pitting corrosion. Both EP and MP nitinol were more susceptible to breakdown in the NaCl than in PBS, indicating that the NaCl provides a more severe test environment than does PBS. Electropolishing increased the breakdown resistance of nitinol in PBS and the NaCl, as found in previous studies with Hank's solution. Surface condition, however, did not have a significant effect on the repassivation behavior of nitinol, as is also the case with titanium. The EP wire and stent showed similar breakdown and repassivation behavior in the NaCl, suggesting that the nature of the EP surface was similar in both cases.

Repassivation Potential of Alloy 22 in Chloride plus Nitrate Solutions using the Potentiodynamic-Galvanostatic-Potentiostatic Method

AbstractIn general, the susceptibility of Alloy 22 to suffer crevice corrosion is measured using the Cyclic Potentiodynamic Polarization (CPP) technique. This is a fast technique that gives rather accurate and reproducible values of repassivation potential (ER1) in most cases. In the fringes of susceptibility, when the environment is not highly aggressive, the values of repassivation potential using the CPP technique may not be highly reproducible, especially because the technique is fast and because transpassive corrosion may influence or mask the nucleation and propagation of crevice corrosion. To circumvent this, the repassivation potential of Alloy 22 was measured using a slower method that combines Potentiodynamic-Galvanostatic-Potentiostatic steps (called here the Tsujikawa-Hisamatsu Electrochemical or THE method). The THE method applies the charge to the specimen in a more controlled way, which may give more reproducible repassivation potential values, especially when the environment is not aggressive. The values of repassivation potential of Alloy 22 in sodium chloride plus potassium nitrate solutions were measured using the THE and CPP methods. Results show that both methods yield similar values of repassivation potential, especially under aggressive conditions.

Corrosion resistance of laser-fabricated metal–matrix composite layer on stainless steel 316L

Laser fabrication of ceramic-reinforced metal–matrix composite (MMC) layer on stainless steel 316L was achieved by a two-step process. Metal–ceramic powders (Ni–WC, Co–WC, Ni–Al2O3, Ni–Cr3C2) and ceramic powders (WC, SiC, CrB2) were preplaced on 316L specimens by flame spraying and pasting, respectively. The preplaced coatings were then irradiated by a high power laser to form MMCs with low (up to 28%) and high (over 80%) volume fractions of ceramic particles. The microstructure and composition of the MMC layers were studied by optical microscopy, scanning electron microscopy, x-ray diffractometry, and image analysis. The corrosion behavior of the laser-fabricated layers in 3.5% NaCl solution at 23 °C was studied by the cyclic potentiodynamic polarization technique. The corrosion resistance of the laser-surfaced specimens varied depending on the type and volume fraction of the reinforcement incorporated. In general, the corrosion potential shifted in the noble direction relative to 316L, but the pitting corrosion resistance deteriorated. Moreover, the results of the present study indicate that a high volume fraction of ceramic particles in an MMC layer was unfavorable for pitting corrosion resistance due to the difficulty in the formation of intact passive films and the presence of vulnerable spots at the ceramic/matrix interface.