Localized corrosion of 15–5 PH and 17–4 PH stainless steel in NaCl solution

The importance in the selection of materials in the aeronautical industry for the manufacture of an aircraft is related to the fact that the materials are present during the life cycle of the aircraft. In particular, the precipitation hardening (PH) stainless steel is used in components that require the combination of excellent mechanical properties, as well as corrosion resistance due to aircraft exposure in harsh environments. Inherently corrosion resistant steels achieve an important characteristic which is passivation by forming a protective layer of chromium oxide on the surface. This research aimed to conduct an analysis of the localized corrosion on stainless steel 15–5 PH and 17–4 PH, used on fasteners or engine components. The steels were evaluated in a 3.5 wt.% NaCl solution, using the electrochemical technique of cyclic potentiodynamic polarization curves (CPP) according to the ASTM 61–86 standard. The microstructural analysis was performed by optical microscopy (OM) and scanning electron microscopy (SEM). The results indicated that CPP curves showed a positive hysteresis, indicating pitting localized corrosion and the corrosion current density of the 15–5 PH and 17–4 PH stainless steels were 1.31 × 10‒8 and 2.70 × 10‒8 A/cm2

Influencia del tratamiento térmico en el comportamiento corrosivo de las aleaciones aluminio-litio AA2099 Y AA2055

Recientemente, las aleaciones de Al-Li han llamado la atención por su uso en estructuras críticas de peso y rigidez utilizadas en aplicaciones aeronáuticas, aeroespaciales y militares ya que presentan mejores propiedades, como baja densidad y alta resistencia especifica en comparación con las aleaciones comerciales de Aluminio. Estos parámetros (densidad y resistencia especifica) no solo son factores de medición de rendimiento de los materiales aeroespaciales, también permiten controlar las dimensiones de la aeronave y los componentes aeroespaciales por medio de las propiedades de la tolerancia al daño y durabilidad. La adición de litio (no mayor al 1.8%) es clave para la reducción de la densidad (por cada 1 % de litio existe una reducción del 3% equivalente a 0.079g/cm3) y un incremento en el módulo elástico (aprox. por cada 1% de litio incrementa un 6%). El objetivo de este estudio es determinar la susceptibilidad a la corrosión localizada de las aleaciones de Aluminio-Litio AA2099 y AA2055 con distintos tratamientos térmicos, T8, T6 y T0 en una solución acida (H2SO4 1%) y en una solución salina (NaCl 3.5%). Se caracterizó electroquímicamente con la técnica de Curva de Polarización Potenciodinámica

Effect of Water on the Stress Corrosion Cracking Behavior of API 5L-X52 Steel in E95 Blend

The effect of water content (0.5%, 1%, 2%, 5%, 10% y 20 V%) in E95 blend (5 V% gasoline – 95 V% ethanol) on the stress corrosion cracking (SCC) susceptibility of X-52 carbon steel was investigated. Slow strain rate tests (SSRT) coupled with electrochemical noise measurements (ECN) were carried out using a strain rate of 1 X 10-6 s-1. In general, scanning electron microscopy (SEM) observations on fracture surfaces showed a ductile behavior. However, secondary cracking was only observed for specimens exposed to solution containing up to 2 V% water. ECN gave indication of a likely localized corrosion process occurring at low water concentrations, whereas for water content above 2 V%, a uniform corrosion process seems more likely to occur. In addition, the material response immersed into the various solutions was investigated by using linear polarization resistance (LPR) measurements, weight loss and pH measurements. Reasons to explain the behavior found are discusse

Corrosion behavior of Zn-TiO2 and Zn-ZnO Electrodeposited Coatings in 3.5% NaCl solution

Electrodeposition is a widely used method to protect metallic materials from corrosion. Electrodeposited coatings provide the metal substrate with both cathodic protection and a barrier effect. The corrosion resistance achieved with this type of zinc-electroplating process in increased by adding nanometric materials to the electrolytic bath. In the present research, coatings were obtained by electrodeposition of pure zinc, Zn-TiO2 and Zn-ZnO nanoparticles. The coatings were generated by immersion in a chloride acid bath applying a current density of 0.05 and 0.10 A/cm2 for 1 min and adding 2 g/l of TiO2 or ZnO nanoparticles. Corrosion behaviour was evaluated with potentiodynamic polarization curves and the electrochemical impedance spectroscopy (EIS) technique using a 3.5% NaCl test solution. After electrochemical testing, the coating surface morphology was analysed by scanning electron microscopy (SEM) and the atomic composition by energy dispersive X-ray spectroscopy (EDS). The electrodeposited coating thickness was measured using the ultrasound technique. The coating thickness was less than 2.5 μm and its corrosion resistance increased with the addition of nanoparticles

Corrosión de titanio y acero quirúrgico en presencia de bacterias orales.

Los implantes dentales están diseñados para restaurar la función y la estética de una pieza dentaria faltante. El titanio posee una alta biocompatibilidad y resistencia a la corrosión. El Acero Quirúrgico 316 es útil en aplicaciones biomédicas para placas o dispositivos ortopédicos. La cavidad oral contiene una amplia carga microbiana: Streptococcus gordonii y Fusobacterium nucleatum son dos bacterias características del biofilm subgingival. La corrosión del metal puede ser un promotor significativo de la pérdida de implantes dentales y aditamentos de acero

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 corrosion behavior of passivated precipitation hardening stainless steels for aerospace applications

Precipitation-hardening (PH) stainless steels (SS) are widely used in various aerospace applications. These steels exhibit good mechanical and corrosion resistance. The electrochemical behavior of 15-5PH, 17-4PH, Custom450 and AM 350 stainless steels passivated with citric and nitric acid baths for 60 and 90 min at 25 and 49 °C were evaluated in 5 wt.% sodium chloride (NaCl) and 1 wt.% sulfuric acid (H2SO4) solutions. The electrochemical behavior was studied with potentiodynamic polarization curves (PPC) according to the ASTM G5-13 standard. The results indicated that there are two characteristic mechanisms that are present in the potentiodynamic polarization curves. When the PHSS is immersed in an H2SO4 solution, there is a secondary passivation, and in the NaCl solution, there is a pseudo-passivation (not stable passivation film). The current densities in the NaCl solution were between 10−4 and 10−5 mA/cm2, while those of H2SO4 were recorded around 10−2 and 10−3 mA/cm2. Citric acid does work as a passivating solution, and in some cases, the corrosion resistance of the stainless steel was comparable to that of nitric acid

Corrosion behavior of AISI 409Nb stainless steel manufactured by powder metallurgy exposed in H2SO4 and NaCl solutions

Powder metallurgy is an effective method for manufacturing stainless steel parts of high quality and accuracy at low cost. However, the use of sintered stainless steels is limited due to their low density, which deteriorates their corrosion resistance. The aim of this study was to determine the corrosion behavior of AISI 409Nb stainless steel specimens sintered with different contents of boron in a hydrogen atmosphere. Boron was added for promoting the formation of a liquid phase during sintering at 1150 °C, thereby achieving a reduction of porosity and increase in density, which is necessary to improve corrosion resistance. The electrochemical techniques of linear polarization resistance (LPR) and electrochemical noise (EN) were used to determine the corrosion behavior of samples with and without additions of boron after immersion in two solutions, 0.5M H2SO4 and 0.5M NaCl. The corrosion rates and the possible corrosion mechanisms in the sintered samples were determined. The results indicate that the samples with boron additions are more prone to corrosion due to chromium carbide precipitation

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

Effect of heat treatment on the electrochemical behavior of AA2055 and AA2024 alloys for aeronautical applications

Since their development, third-generation aluminum–lithium alloys have been used in aeronautical and other applications due to their good properties, replacing conventional Al-Cu and Al-Zn alloys and resulting in an increase in payload and fuel efficiency. The aim of this work was to investigate the influence of different heat treatments on the electrochemical corrosion behavior of the alloys AA2055 and AA2024 in the presence of three different electrolytes at room temperature, using an electrochemical noise (EN) technique in accordance with the ASTM-G199 standard. In the time domain, the polynomial method was employed to obtain the noise resistance (Rn), the localization index (IL), skewness, and kurtosis, and in the frequency domain, employing power spectral density analysis (PSD). The microstructure and mechanical properties of the alloys were characterized using scanning electron microscopy (SEM) and the Vickers microhardness test (HV). The results demonstrated better mechanical properties of the AA2055 alloy, which had a Vickers hardness of 77, 174, and 199 in the heat treatments T0, T6, and T8, respectively. An electrochemical noise resistance (Rn) of 2.72   105 W cm2 was obtained in the AA2055 T8 alloy evaluated in a NaCl solution, while the lowest Rn resistance of 2.87   101 W cm2 occurred in the AA2024 T8 alloy, which was evaluated in a HCl solution. The highest electrochemical noise resistance (Rn) was obtained in the AA2055 alloys, which had received the T6 and T8 heat treatments in the three solutions