Electrochemical Corrosion of Ferritic 409 and 439 Stainless Steels 409 and 439 in NaCl and H2SO4 solutions

Over the time the automotive industry has evolved in the use of steels in different parts of vehicles, thanks to the materials technology; a deciding factor in the market are the corrosion properties. Based on this fact, it was decided the incorporation of stainless steels (SS), especially in parts which are exposed to environment, such as exhaust pipes, where the 409 SS tops the production list and in some cases replaced by the 439 SS. This study makes a comparative performance evaluation between ferritic steels 409 and 439, in different electrolytes that are important to automotive industry like 5% brine as simulating saline environment, 3.5% sulfuric acid (H2SO4) solution and water as the blank, with the purpose to identify their corrosion behavior. Given the characteristics of stainless steel 409 and 439, is expected pitting, so mechanistic electrochemical techniques are used, such as cyclic potentiodynamic polarization curves and electrochemical noise. The corrosion kinetics indicated that the 439 stainless steel in H2SO4 had the highest corrosion rate, while in NaCl the 409 had the highest. Both materials have a pitting corrosion type in sodium chloride using cyclic polarization curves and electrochemical noise techniques for its evaluation

Electrochemical characterization of Al–Li alloys AA2099 and AA2055 for aeronautical applications: effect of thermomechanical treatments

Third-generation Al–Li alloys are high-performance materials that are very attractive for aircraft and aerospace applications due to their relatively low density, high specific strength, and stiffness. To study the effect of heat treatments on the electrochemical behavior of two high-performance aluminum-lithium alloys, in this work the electrochemical noise technique was used to evaluate the corrosion behavior of AA2099 and AA2055 alloys under three conditions of different heat treatments, an annealing treatment (T0), a second treatment in solid solution, followed by rapid cooling (quenching) and subsequent artificial aging (T6), and a third treatment in solid solution, tempering, cold deformation, and maturation artificial (T8). The time series obtained from the electrochemical noise tests were visually analyzed, as well as the statistical parameters such as localization index (LI), bias, and kurtosis. Analysis in the frequency domain was also performed by means of power spectral density (PSD) signals. In general, it was observed that the distribution of precipitates on the surface of the alloys considerably affects the corrosion performance, as well as the concentration of Cl-1 ions in the test electrolytes

Electrochemical Behaviour of Galvanized Steel Embedded in Concrete Exposed to Sand Contaminated with NaCl

This research evaluates the corrosion of reinforced concrete, exposed to marine sand, simulating what happens with the elements of laying of foundations of all concrete structures constructed on coasts of Mexico and the world. In such concrete specimens a steel bar AISI 1018 and Galvanized Steel was embedded as reinforcement, the mixed concrete was of ratio w/c=0.45 (f´c = 350 kg / cm2), according to ACI 211.1, using two type cements CPC 30R and CPC 30R RS. The corrosion rate was evaluated by electrochemical techniques, corrosion potential Ecorr (ASTM C-876-09) and Linear Polarization Resistance (ASTM-G59). These specimens were exposed in a marine sand contaminated with 0, 1, 2 and 3% NaCl, the exposure time was 260 days where, according to the electrochemical results of Ecorr and Icorr, we could determine that the better performance of the specimens was galvanized steel and concrete made with cement CPC 30R RS, this research demonstrated the importance of developing special to elaborated concrete durability in aggressive environment such as is the ground where uproots all reinforced concrete structures

Estudio del comportamiento de la corrosión de los aceros inoxidables am 350 y custom 450 pasivados en medio ácidos

En este trabajo se estudia el comportamiento de los aceros inoxidables AM 350 y Custom 450 en medios corrosivos de NaCl al 5% y H2SO4 al 1%. Los cuales fueron pasivados en ácido cítrico y ácido nítrico, a temperaturas de 25 y 49oC, con tiempos de inmersión de 60 y 90 minutos. La técnica Electroquímica empleada fue Polarización potenciodinámica, utilizando un potenciostato/galvanostato/ZRA "Gill AC Instruments". Las demandas de corriente en solución de NaCl son de 10-4 mA/cm2, mientras que las de H2SO4 están alrededor de 10-2 y 10-3 mA/cm2. También se realizó la determinación de la microestructura de los materiales establecidos, su morfología y composición química, a través de la microscopía óptica y microscopía electrónica de barrido. Se comprobó que el que ácido cítrico funciona como solución pasivante y en algunos casos la resistencia a la corrosión es equiparable con la del ácido nítrico

Corrosion Behaviour of 304 Austenitic, 15-5PH and 17-4PH Passive Stainless Steels in acid solutions

The objective of this work was to study is use electrochemical techniques to determinate the growth conditions, characteristics and resistance of passive layers of stainless steel (SS): 304 austenitic, 17-4PH (precipitation hardening) and 15-5PH. Passivation of the SS was performed in 15% citric acid at temperatures of 25 and 49 °C. The corrosion kinetics was obtained using the electrochemical technique as potentiodynamic polarization (PP), in a three-electrode system. The electrolytes used were sodium chloride (5 wt. % NaCl) and sulfuric acid (1 wt. % H2SO4). Passivation in citric acid allows obtain passive layers at temperatures of 49°C with immersion times of 30 minutes. In precipitation hardening steels, passive layers up to 360 mV in sodium chloride. Can be obtained. In sulfuric acid, there is a mechanism of passivation – transpassivation - secondary passivation, this due to the high electropositive values of potential

Cyclic potentiodynamic polarization on titanium alloys anodizing in alkaline solutions

Titanium alloys are used in different industries such as biomedical, aerospace, aeronautic, chemical, and naval. Those industries have high requirements with few damage tolerances. The aim of this work was to study the corrosion behavior of titanium alloys anodizing and non-anodizing in alkaline (KOH and NaOH) solutions, exposed in 3.5%wt. NaCl and 3.5% wt. H2SO4 solutions at room temperature using cyclic potentiodynamic polarization (CPP) according to standards in order to obtain electrochemical parameters as the passivation range (PR), corrosion type, passive layer persistence, corrosion potential (Ecorr), and corrosion rate. The alloy Ti Beta-C anodized presented better corrosion resistance than Ti-6Al-4V in both media. The smallest corrosion rate is presented in Beta-C samples (4.72 E-8 A/cm2) and the highest corrosion rate is CP2 (1.61 E-5 A/cm2

Corrosion behavior of aluminum-carbon fiber/epoxy sandwich composite exposed on NaCl solution

For years, the aeronautical industry has employed different types of materials to satisfy its high-performance requirements. Fiber-metal laminates are used due to their combination of lighter weight and the high mechanical properties of reinforced metal and carbon. We therefore made two different composites of laminate-metal and laminate-metal-laminate of carbon fiber-reinforced polymer and aluminum with an ALCLAD layer. The samples were characterized by salt fog (0, 48, and 96 h) at 5 wt% NaCl and electrochemical impedance spectroscopy (EIS) with an electrolyte of 3.5 wt% NaCl. All samples were studied by electron scanning microscopy (SEM). The results demonstrated that the samples of laminate-metal-laminate presented an adsorption process after 0 and 48 h of salt fog exposition; meanwhile, the samples of laminate-metal showed a capacitive behavior for all the samples; however, corrosion resistance decreased when the salt fog exposition time increased

Parameter Studies on High-Velocity Oxy-Fuel Spraying of CoNiCrAlY Coatings Used in the Aeronautical Industry

The thermal spraying process is a surface treatment which does not adversely affect the base metal on which it is performed. The coatings obtained by HVOF thermal spray are employed in aeronautics, aerospace, and power generation industries. Alloys and coatings designed to resist oxidizing environments at high temperatures should be able to develop a surface oxide layer, which is thermodynamically stable, slowly growing, and adherent. MCrAlY type (M = Co, Ni or combination of both) coatings are used in wear and corrosion applications but also provide protection against high temperature oxidation and corrosion attack in molten salts. In this investigation, CoNiCrAlY coatings were produced employing a HVOF DJH 2700 gun. The work presented here focuses on the influences of process parameters of a gas-drive HVOF system on the microstructure, adherence, wear, and oxygen content of CoNiCrAlY. The results showed that spray distance significantly affects the properties of CoNiCrAlY coatings

Corrosion resistance of titanium alloys anodized in alkaline solutions

Titanium alloys present superior electrochemical properties due to the generation of the TiO2 passive layer. The ability to generate an oxide passive layer depends on the anodized alloy. This work mainly studies the corrosion resistance of the alloys Ti-6Al-2Sn-4Zr-2Mo and Ti-6Al-4V anodized in NaOH and KOH at 1 M and 0.025 A/cm2 of current density. The electrochemical techniques were performed in a conventional three-electrode cell exposed to electrolytes of NaCl and H2SO4. Based on ASTM-G61 and G199, cyclic potentiodynamic polarization (CPP) and electrochemical noise (EN) techniques were used. The results indicated that Ti-6Al-2Sn-4Zr-2Mo anodized on NaOH presented a higher passivity range than anodized on KOH, relating to the high reactivity of Na+ ions. The former anodized alloy also demonstrated a higher passive layer rupture potential. In EN, the results showed that Ti-6Al-4V anodized in KOH presented a trend toward a localized process due to the heterogeneity of anodized porosity and the presence of V in the alloy