Showing papers in "Materials and Corrosion-werkstoffe Und Korrosion in 2007"
TL;DR: In this article, the electrochemical behavior of three titanium alloys, namely Ti-13Nb-13Zr, Ti-6A1-4V and Ti- 6A 1-7Nb, for implant materials was evaluated in Hanks' solution by electrochemical techniques.
Abstract: In this investigation the electrochemical behaviour of the Ti-13Nb-13Zr, Ti-6A1-4V and Ti-6A1-7Nb alloys, for application as implant materials was evaluated in Hanks' solution by electrochemical techniques. The alloys were immersed in this solution for 410 days and periodically they were tested by electrochemical impedance spectroscopy. At the end of this period, polarization curves of the three titanium alloys were obtained. The electrochemical impedance experimental results were interpreted using an equivalent electrical circuit that simulates a duplex structure oxide composed of an inner compact layer, here called barrier layer, and an outer and porous layer. The results indicated that all the alloys present a very high corrosion resistance in the electrolyte used, typical of passive alloys, and that the corrosion resistance is mainly due to the barrier layer. The passive like behaviour was maintained during the whole period of test.
120 citations
TL;DR: In this paper, the role of plasma spraying on superalloys has been discussed with the help of a comprehensive literature survey, and the main focus of this investigation is the studies related to plasma sprayed NiCrAlY, Ni-Cr, Nickel aluminide and Co-based coatings.
Abstract: High temperature oxidation is one of the main failure modes of the hot-section components in gas turbines, boilers, waste incinerations, diesel engines, coal gasification plants, chemical plants and other energy generation systems. In such applications the use of Fe-, Ni- and Co-based alloys, especially of superalloys is well known. The superior mechanical strength and good corrosion resistance of the superalloys at high temperature make them favorites for such applications. However, the presence of combustion gases constitutes an extreme environment and hot corrosion is inevitable when superalloys are used at high temperatures for long durations of time. Therefore these alloys need to be protected against this type of oxidation. Several countermeasures have been suggested in the literature to combat the same. One such countermeasure against hot corrosion and oxidation constitutes the deposition of protective coatings on these alloys. Among the various techniques used for deposition of coatings, plasma spraying is a versatile technology that has been successful as a reliable cost-effective solution for many industrial problems. It allows the spraying of a wide range of high performance materials from superalloys and refractory intermetallic compounds to ceramics with continuously increasing commercial applications. Furthermore it does not cause deterioration of the substrate alloys, and relatively thick coatings can be formed with high deposition rates. In this paper the technique of plasma spraying has been detailed and the role of plasma sprayed coatings to arrest high temperature oxidation has been discussed with the help of a comprehensive literature survey. The main focus of this investigation is the studies related to plasma sprayed NiCrAlY, Ni-Cr, Nickel aluminide and Co-based coatings.
107 citations
TL;DR: In this article, the influence of potential on electrochemical behavior of pure Ti, Ti-6Al-7Nb, and Ti 6Al-4V ELI alloy under saline conditions were investigated by electrochemical impedance spectroscopy (EIS).
Abstract: The influence of potential on electrochemical behaviour of pure Ti, Ti-6Al-7Nb, and Ti-6Al-4V ELI alloy under saline conditions were investigated by electrochemical impedance spectroscopy (EIS). All measurements were carried out in saline solution (0.9% NaCI) at different impressed potentials (corrosion potential (E Corr ), 0 mV (SCE) and + 500 mV (SCE)) for 1 h. The experimental results were compared with those obtained by potentiodynamic polarization curves. The corrosion current densities obtained for the titanium alloys showed lower values than for pure Ti, indicating the formation of a stable passive film with time. Electrochemical impedance spectroscopic studies indicated that the resistance of the passive film increased with the impressed potential. The impedance spectra were fitted using a non-linear least square (NLLS) fitting procedure. The magnitude of the corrosion resistance of titanium alloys under saline solution was compared and results are presented.
81 citations
TL;DR: In this paper, rare earth Ce (cerium) was added to the Mg-Ce master alloy to improve the corrosion resistance of AZ91 by decreasing the size of β-Mg 17 Al 12 and enhancing the protective effectiveness of corrosion products.
Abstract: A novel AZ91 Ce containing magnesium alloy characterized by excellent corrosion resistance is fabricated by adding rare earth Ce (cerium) in the form of a Mg-Ce master alloy. The metallographic investigation shows that Ce added to AZ91 can obviously decrease the size of β-Mg 17 Al 12 and forms Al 11 Ce 3 intermetallic compounds in the shape of fine needles. The corrosion tests and electrochemical measurements indicate that the corrosion resistance of AZ91 Ce containing magnesium alloy is obviously higher than that of AZ91. Furthermore, increasing the content of Ce in the magnesium alloy can further enhance the corrosion resistance. X-ray photoelectron spectroscopy (XPS) reveals that Ce can be incorporated into corrosion products in the form of CeO 2 in the course of corrosion. Based on the preliminary analysis, the addition of Ce can improve the corrosion resistance of AZ91 by decreasing the size of β-Mg 17 Al 12 and enhancing the protective effectiveness of corrosion products.
65 citations
TL;DR: In this article, the behavior of Ti-6Al-4V and the new experimental Ti-23Ta has been evaluated in artificial saliva of pH 2, 5 and 7 and different F-concentrations (0, 1000, 5000 and 10000 ppm), through open circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy.
Abstract: Titanium alloys exhibit an excellent corrosion resistance in most aqueous media due to the formation of a stable oxide film and some of these alloys (particularly Ti-6Al-4V) were chosen for surgical and odontological implants for this resistance and their biocompatibility. Treatments with fluorides (F - ) are known as the main method to prevent plaque formation and dental caries. Toothpastes, mouthwashes and prophylactic gels can contain from 200 to 20 000 ppm F - and can present neutral to acidic character, which can affect the corrosion behavior of titanium alloys devices present in the oral cavity. In this work, the behavior of Ti-6Al-4V and the new experimental Ti-23Ta has been evaluated in artificial saliva of pH 2, 5 and 7 and different F-concentrations (0, 1000, 5000 and 10000 ppm), through open-circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. A defined correlation between pH and F - concentration settled the active or passive character of the materials. For both alloys, an active behavior was observed for pH 2 and 1000 to 10 000 ppm F- and for pH 5 and 5000 and 10 000 ppm F-. The passive behavior was observed for the other investigated conditions. The F - concentration increase and pH decrease reduced the corrosion resistance of the alloys and decreased the stability of their passive film. The corrosion behavior of both alloys was very similar, but the Ti-23Ta alloy generally presented slightly higher corrosion resistance.
62 citations
TL;DR: In this paper, a parametric study is carried out to investigate the effect of variations in anodic and cathodic Tafel slopes, exchange current densities and electrode potentials on the rate of steel corrosion in concrete.
Abstract: A parametric study is carried out to investigate the effect of variations in anodic and cathodic Tafel slopes, exchange current densities and electrode potentials on the rate of steel corrosion in concrete. The main goal of this investigation is to identify the parameters that have significant influence on steel corrosion rate. Since there is a degree of uncertainty associated with the selection of these parameters, particularly during modelling exercises, it is intended that the results of this study will provide valuable information to engineers and researchers who simulate steel corrosion in concrete. To achieve this goal, the effect of a parameter on the corrosion rate of steel is studied while all other parameters are kept constant at a predefined base case. For each parameter, two extreme cases of anode-to-cathode ratio are studied. The investigation revealed that the variations in the anodic electrode potential have the greatest impact on the corrosion rate, followed by the variations in the cathodic Tafel slope.
61 citations
TL;DR: In this article, a numerical model for predicting the corrosion rate of uniformly depassivated steel in concrete is developed, which is built on Stern's earlier work that an optimum anode-to-cathode ratio exists for which the corrosion current on the metal surface reaches a maximum value.
Abstract: The quantification of active corrosion rate of steel in concrete structures through nondestructive methods is a crucial task for scheduling maintenance/repair operations and for achieving accurate service life predictions. Measuring the polarization resistance of corroding systems and using the Stern-Geary equation to calculate the corrosion current density of active steel is a widely-used method for this purpose. However, these measurements are greatly influenced by environmental factors; therefore, accurate monitoring of corrosion requires integrating the instantaneous corrosion rates over time. Although advanced numerical models are helpful in research settings, they remain to be computationally expensive and complex to be adopted by general engineering community. In this paper, a practical numerical model for predicting corrosion rate of uniformly depassivated steel in concrete is developed. The model is built on Stern's earlier work that an optimum anode-to-cathode ratio exists for which the corrosion current on the metal surface reaches a maximum value. The developed model, which represents the corrosion rate as a function of concrete resistivity and oxygen concentration, is validated using experimental data obtained from the literature.
49 citations
TL;DR: In this paper, a rotating disc electrode is used for electrochemical measurements, which enables model defined flow conditions on the surface of the underlying magnesium alloy to be better characterized using a rotating sensor.
Abstract: The corrosion behaviour of magnesium alloys is not substantially comparable to other metals, such as iron, nickel and copper. It is always accompanied by hydrogen evolution. More hydrogen is evolved at a more positive potential or a higher anodic current density. The ‘strange’ hydrogen evolution behaviour is a common phenomenon for magnesium alloys and it is called negative difference effect (NDE). The NDE continues to receive considerable discussion.
Furthermore, the corrosion behaviour of magnesium alloys depends mainly on the pH value of the surrounding electrolyte. Voluminous reaction products, formed in neutral electrolytes, lead to a diffusion-controlled dissolution on the surface of the underlying magnesium alloy. Therefore, influences from structure and alloying are suppressed very strongly. In alkaline environments, passivation occurs as a result of the formation of a hydroxide layer on the magnesium surface. Therefore, differences in the corrosion behaviour between the alloys are hardly detectable. Measurable effects can only be detected using very ‘aggressive’ corrosion conditions. Present methods do not adequately take into account the specific character of the corrosion of magnesium alloys. It can be better characterized using a rotating disc electrode for electrochemical measurements, which enables model defined flow conditions on the surface. Furthermore, the application of electrochemical noise offers the possibility of a simple and sensitive assessment of the corrosion susceptibility of magnesium alloys. Due to the high sensitivity of this measurement procedure, it is also possible to carry out examinations under more practical conditions.
46 citations
TL;DR: In this article, the corrosion behavior of Ti-5Al-2Nb-1Ta alloy in Hanks solution at different immersion periods (0 h, 120 h, 240 h and 360 h).
Abstract: Electrochemical polarization and impedance spectroscopic (EIS) techniques were used to investigate the corrosion behavior of Ti-5Al-2Nb-1Ta alloy in Hanks solution at different immersion periods (0 h, 120 h, 240 h and 360 h). The impedance spectra are fitted using a non-linear least square (NLLS) fitting procedure. The EIS spectra exhibited a two time constant system, suggesting the formation of two layers on the metal surface. The surface morphology of the alloy has been characterized by SEM and EDAX measurements.
46 citations
TL;DR: In this article, the authors used 50 Hz AC anodizing technique in an alkaline borate solution, which contained a new kind of organic additive and without F, P, and Cr. They found that the formation of the anodic films was always coupled with sparking and oxygen evolution.
Abstract: Plasma electrolytic oxidation (PEO) of Mg-based AZ91D alloys was investigated using 50 Hz AC anodizing technique in an alkaline borate solution, which contained a new kind of organic additive and without F, P, and Cr. The anodizing technological parameters have been optimized and a kind of ivory-white smooth anodic film with high corrosion resistance was obtained. It was found that the formation of the anodic films was always coupled with sparking and oxygen evolution, whose intensity changed with the additive and anodizing voltage. All EIS plots have two capacitive loops and one low frequency inductive component. Two capacitive arcs present the barrier and porous layer of the PEO film and the inductive component in the low frequency domain is a complex behavior due to the porous structure connected to the electrolyte.EIS plots and fitting results show that a self-sealing process of the PEO firm with different additives takes place in the beginning of immersion time, then corrosion attack becomes a preponderant process to promote the degradation of the film. Tafel results show that PEO treatment decreases the corrosion current density by four, even five orders of magnitude, while additives content does not affect strongly the electrochemical corrosion behavior. Salt spray test shows that the PEO film formed with NaAlO2 and Na2SiO3 presents good corrosion resistance, over 600 h without any sealing treatment. The difference of corrosion resistance arose by additives examined by electrochemical techniques and salt spray test does not show strict corresponding relationship.
45 citations
TL;DR: In this paper, the authors compared the corrosion properties of different titanium alloys, such as Ti6Al7Nb, Ti 6Al2Nb1Ta1Nb and Ti5Al2.5Fe, with the commercial titanium, regarding the corrosion resistance in artificial saliva.
Abstract: In the last decade, new titanium alloys have been developed in different areas of dentistry, such as Ti6Al7Nb, Ti6Al2Nb1Ta1Nb, and Ti5Al2.5Fe. The aim of this study was to compare the Ti6Al7Nb, Ti6Al2Nb1Ta1Nb, Ti5Al2.5Fe, and Ti6Al4V alloys with the commercial titanium, regarding the corrosion resistance in artificial saliva. In the electrochemical estimations the polarization data are converted into instantaneous corrosion rate values (Icorr). The passivation properties were comparable for the four alloys. The EIS spectra are best fitted using an equivalent circuit (EC), which corresponds to the model of a two-layer structure for the passive film. High impedance values (in the order of 106 Ω cm2) were obtained from medium to low frequencies for all materials suggesting high corrosion resistance in artificial saliva.
The electrochemical and corrosion behavior of Ti6Al4V is not affected on substituting vanadium with niobium, iron, molybdenum, and tantalum.
TL;DR: In this article, the corrosion performance of Ni-P-ZrO 2 composite coating was compared with that of NiP coating with 3.5% NaCl solution and showed that NiP was superior to NiP.
Abstract: Electroless Ni-P-ZrO 2 and Ni-P coatings on AZ91D magnesium alloy were prepared, and their corrosion protection properties were compared in this paper. The potentiodynamic curves and electrochemical impedance spectroscopy (EIS) of the coated magnesium alloy in 3.5% Nacl solution showed that the corrosion performance of Ni-P-ZrO 2 composite coating was superior to that of Ni-P coating. The same conclusion was obtained with salt spray and immersion tests. The corrosion morphologies of two kinds of coatings with various immersion time intervals in 3.5% NaCl solution indicated that most corrosion products concentrated on the nodules boundaries of Ni-P coating and blocked corrosion pit was the main corrosion form. For the Ni-P-ZrO 2 coating, tortuous nodules boundaries were not the weak sites of the coating and corrosion initiated from the nickel phosphor alloy around the nanometer powders. Open corrosion pits occurred on the composite coating surface, and the coating was corroded gradually. Thus, the Ni-P-ZrO 2 coating exhibited better corrosion protection property to magnesium alloy substrate than Ni-P coating.
TL;DR: The release rates of total copper in artificial seawater (without organic matter) from anti-fouling paints of different active copper compounds range from 0.5 to 75 μg cm-2 day-1 as discussed by the authors.
Abstract: Release rates of total copper in artificial seawater (without organic matter) from anti-fouling paints of different active copper compounds range from 0.5 to 75 μg cm-2 day-1. Approximately 80% of ...
TL;DR: In this article, two types of aluminum alloys, 2024-T3 and 7075-T6, have been selected in order to investigate the effect of metallurgical aspects on exfoliation corrosion.
Abstract: Two types of aluminum alloys, 2024-T3 and 7075-T6, have been selected in this study to investigate the effect of metallurgical aspects on exfoliation corrosion. To determine and evaluate the metallurgical effects of heat treatments on corrosion behaviour of these alloys, G34 ASTM test was selected to investigate the exfoliation corrosion behaviour. The results showed that with increasing the aging time for the aluminum alloy type 2024-T3 the susceptibility to exfoliation corrosion increases, while for type 7075-T6 decreased. These results refer to precipitation of the intermetallic compound phases such as CuAl 2 , and MgZn 2 , in 2024-T3 and 7075-T6 respectively. The amount of these phases increases with increasing the aging time for both alloys. The investigations showed the phases that initiate in 2024-T3 act as anode sites while in 7075-T6 they act as cathode sites.
TL;DR: In this article, the electrochemical behavior of the titanium and Ti-6Al-7Nb alloy in artificial saliva was analyzed and the results revealed a high biocompatibility between HOB and the alloy.
Abstract: In this paper, the electrochemical behaviour of the titanium and Ti-6Al-7Nb alloy in artificial saliva (TaniZ 5; 6.7; 9; the total quantity of ions released in the artificial saliva and corrosion rates are very low, proving a very good corrosion resistance and very low toxicity. In undoped and doped Carter-Brugirard saliva, the open circuit potentials have highly electropositive values, denoting passive state and good stability; the open circuit potential gradients, simulating the non-uniformity of the saliva composition, show very low values, no danger for the implant integrity. The in vitro cytotoxicity of Ti-6Al-7Nb alloy was evaluated on the basis of cell morphology and cell viability. The results obtained revealed a high biocompatibility between HOB and Ti-6Al-7Nb alloy.
TL;DR: In this article, the accumulation process of sulfate reducing bacteria (SRB) biofilms established in anaerobic stagnant batch bioreactors on the surface of carbon steel and the nutrient transport and corrosion products distribution in it were characterized by X-ray Photoelectron Spectroscopy (XPS).
Abstract: The accumulation process of sulfate reducing bacteria (SRB) biofilms established in anaerobic stagnant batch bioreactors on the surface of carbon steel and the nutrient transport and corrosion products distribution in it were characterized by X-ray Photoelectron Spectroscopy (XPS). In addition, the corrosion occurrence and development of carbon steel under SRB biofilm was investigated by Electrochemical Impedance Spectroscopy (EIS) in-situ. The results show that the thickness of SRB biofilms increases exponentially with time in the beginning and after 14 days reaches a maximum. From then on, the accumulation rate decreases to zero. In mature biofilms, SRB dispersed throughout the biofilm. In the inner layer near the substrate, due to the high sulfate-reducing activity of SRB, corrosion products such S 2- , H 2 S and organic acid are present, which lead to corrosion occurrence and development. In the outer layer of the biofilm SRB can also reduce the SO 2- 4 to SO 2- 4 and S 2 O 2- 3 . This metabolism process enhances the Fe 2+ transfer from the inner to the outer side. The activity of SRB in the biofilm plays a key role in the initial corrosion process.
TL;DR: In this article, the interdiffusion between aluminide coatings and steel substrates was studied for times up to 10,000 h in the temperature range of 500-800 °C.
Abstract: One of the potential degradation modes of oxidation-resistant iron aluminide coatings is the loss of Al from the coatings into Fe-base substrate alloys that typically contain no Al. To address this issue, interdiffusion between aluminide coatings and steel substrates was studied for times up to 10,000 h in the temperature range of 500-800 °C. Coatings were synthesized in a laboratory chemical vapor deposition (CVD) reactor on representative commercial ferritic alloy Fe-9Cr-lMo and type 304L austenitic stainless steel. The microstructural and compositional changes after diffusion anneals were examined in detail. An initial attempt to model the interdiffusion behavior was carried out by applying an existing software program COSIM (coating oxidation and substrate interdiffusion model). Complementary work was conducted using a simple mathematic model developed by Heckel et al. Reasonable agreement was observed between the simulated and experimental composition profiles for the aluminide coatings on ferritic alloys. Model results were then applied to predict coating lifetime.
TL;DR: In this paper, a coating with a thickness of approximately 30 μm was applied to the surface of aluminum alloy 3003, and after creating an artificial defect by means of a knife-edge, a corrosion test was carried out in 3% NaCl solution at a temperature of 70°C and pH 1.5.
Abstract: Several types of coatings, designed to improve the resistance of aluminum alloys to corrosion in seawater, were examined. A coating with a thickness of approximately 30 μm was applied to the surface of aluminum alloy 3003, and after creating an artificial defect by means of a knife-edge, a corrosion test was carried out in 3% NaCl solution at a temperature of 70°C and pH 1.5. The test results showed that a fluorine resin and sol-gel coatings both had excellent barrier abilities. The fluorine resin coating had self-healing abilities, and this was improved by the addition of a metal powder.
TL;DR: In this paper, the influence of (2E)-3-amino-2-phenylazo-but-2enenitrile and its derivative as corrosion inhibitors for copper in 0.5 M HNO 3.
Abstract: The objective of this work is to provide additional insight on the influence of (2E)-3-amino-2-phenylazo-but-2-enenitrile and its derivative as corrosion inhibitors for copper in 0.5 M HNO 3 . Electrochemical techniques (potentiodynamic polarization, polarization resistance and impedance spectroscopy) as well as weight loss measurements have been employed to study the corrosion inhibition. The investigated compounds have shown inhibition efficiency in 0.5 M HNO 3 . Inhibition efficiency of these compounds has been found to vary with the concentrations of the compounds. The adsorption of these compounds on the copper surface from the acid solution has been found to obey Langmuir adsorption isotherm. The results revealed that the compounds are mixed type inhibitors. The effect of temperature on the inhibition efficiency was studied.
TL;DR: In this article, a permanganate-rare earth metal salt (REMS) chemical conversion bath was applied to a sample of AZ91 magnesium alloy and a red-brown conversion coating formed subsequently on the sample surface.
Abstract: A permanganate-rare earth metal salt (REMS) chemical conversion bath was applied to a sample of AZ91 magnesium alloy in this study, a red-brown conversion coating formed subsequently on the sample surface. The test results of this coating with a scanning electron microscope (SEM) showed that there existed net-like cracks on the surface of the treated magnesium alloy. With the analyses of X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS), a further study of this coating indicated that the coating was structurally amorphous and mainly composed of CeO 2 , MnO, MnO 2 , MgO, Mg(OH) 2 and MgAl 2 O 4 . Furthermore, the electrochemical polarization tests showed that compared with the samples treated by the chrome-based method, the open-circuit potential of the magnesium alloy coated in permanganate-REMS bath moved from - 1.34 V SCE to - 1.28 V SCE and the anodic current density of the alloy, at the same potential, decreased evidently in simulated sweat fluid. The cracks in the chemical conversion coating should be caused by the phase structure of the magnesium alloy. During the chemical conversion process, the localized corrosion micro-cell led to the formation of the net-like cracks on the surface. Simultaneously, the dehydration of the surface coating after treatment also accelerated the formation of the cracks at the coating surface.
TL;DR: In this paper, the effect of SRB on the plasticity loss of ferrite-pearlite and sorbite steels was investigated in synthetic sea water at potentials corresponding to the cathodic protection.
Abstract: At the slow strain rate tensile tests done using the specially designed facility, the decrease in the elongation to fracture, reduction of area, fracture energy and no effect on the strength have been stated for the low alloy ferrite-pearlite and sorbite steels, polarized in synthetic sea water at potentials corresponding to the cathodic protection (- 800 to - 1400 mV SCE ). Presence of SRB promotes the plasticity loss, being especially pronounced at potentials - 1100 to - 1200 mV SCE . At higher cathodic polarization, the plasticity estimated in inoculated and in sterile water equalizes. The effects have been correlated with the contents of absorbed and of permeable hydrogen. The promotion of hydrogen charging and the plasticity loss by SRB at the low and medium applied cathodic polarization has been accounted for the observed production of S -2 ions and inhibition of deposit formation. The negligible effect of SRB at the high cathodic polarization has been suggested to be a result of the suppression the SRB growth due to the high alkalization of the near surface solution. The same amount of hydrogen produces the less detrimental effect on the sorbite than on the ferrite-pearlite steel. However, at the similar cathodic polarization, the sorbite steel absorbs the highest amount of hydrogen and reveals the most pronounced degradation. Cathodic protection of constructions subjected to the action of SRB in the sea water should provide the conditions, under which no fragment of marine construction could be polarized by potential corresponding to the maximum degradation of the plastic properties of steels (- 1100 to - 1200 mV SCE ).
TL;DR: In this article, the influence of overaging to the T7451 temper on the microstructure, the mechanical properties, and the corrosion susceptibility of friction-stir-welded 7075 aluminum alloy was investigated by means of transmission electron microscope (TEM), SEM investigations, constant extension rate tests (CERT), alternate immersion tests, and potentiodynamic scans.
Abstract: The influence of overaging to the T7451 temper on the microstructure, the mechanical properties, and the corrosion susceptibility of friction-stir-welded 7075 aluminum alloy was investigated by means of transmission electron microscope (TEM), SEM investigations, constant extension rate tests (CERT), alternate immersion tests, and potentiodynamic scans The overaging that occurs during welding within the heat-affected zones of the friction-stir-welded 7075-O tempered plates promotes a slight formation of intragranular and grain boundary precipitates and increases the mechanical as well as the corrosion resistance properties as compared to the T7451 welded plates The "double" overaging treatment, consisting of the T7451 temper and the thermal transient experienced by the heat-affected zones of the 7075-T7451 welded plates, increases the size of the intragranular and the grain boundary precipitates as well as the precipitate-free zones These facts decrease the mechanical and corrosion properties of the 7075-T7451 weld The T7451 thermal treatment applied after the welding of the 7075-O plates promotes the high presence of small precipitates and reduces the size of the precipitate-free zones This fact increases the general corrosion resistance, but decreases the mechanical properties Therefore, the corrosion as well as the mechanical properties are greatly correlated with minute changes in the microstructure, which can arise by short-term heat exposure as for instance during welding It was also found that the environmental susceptibility measured by means of CERTs may be influenced by "solution-strengthening" corrosion mechanisms which increase the strain This fact is present in weld microzones particularly susceptible to corrosion
TL;DR: In this article, anodic oxide films were grown on Al7075-T6 and the Al/SiC composite by sulfuric acid anodizing and sealing in a cold saturated solution of nickel acetate.
Abstract: Electrochemical impedance spectroscopy (EIS) and the scanning electron microscope (SEM) have been used in an investigation of the effectiveness of various sealing methods that can be used to improve the corrosion resistance of an anodized aluminum-silicon carbide (Al/SiC) composite. Anodic oxide films were grown on Al7075-T6 and the Al/SiC composite by sulfuric acid anodizing and sealing in a cold saturated solution of nickel acetate. Other samples were sealed using the traditional method of boiling water or hot nickel acetate for comparison. The results revealed a uniform anodized layer on Al7075-T6 that resisted pitting corrosion for more than 2 weeks exposure to NaCl, whereas a cracked oxide film with variations in thickness was observed on the composite material. Pit initiation occurred in less than 5 days on the anodized Al/SiC that was sealed in the hot solutions. This study suggests that the traditional hot sealing methods did not provide sufficient corrosion protection for aluminum metal–matrix composites (MMCs) because the reinforcing SiC particles deteriorated the surface film structure. However, this defective film can be repaired by nickel hydrate precipitation during cold sealing or by applying a thick polyurethane coating.
TL;DR: In this paper, a magnesium alloy was melted by CO 2 laser and compared with as-received Mg alloy, the grain of the melted layer was refined significantly and the content of Al was increased.
Abstract: AZ91HP magnesium alloy was melted by CO 2 laser. Compared with as-received Mg alloy, the grain of the melted layer was refined significantly and the content of Al was increased. The corrosion resistance of the melted layer was improved because of the grain refinement, the redistribution of β-Mg 17 Al 12 and the increasing of the Al content. As compared to the non-overlapping zone, the overlapping zone of the melted layer was liable to be corroded.
TL;DR: In this paper, the zinc mass loss has been related to several independent parameters, presenting linear equation, which indicates the air contaminant SO 2 as the major factor controlling the runoff of zinc.
Abstract: Zinc and hot dip galvanized steel are frecuently used metals in building application. They have relatively good atmospheric resistance to corrosion, due to its oxidation in air and formation of protective rust on its surface, which acts as barrier between the metal and environment. However, some part of the rust can be dissolved by pluvial precipitations and water condensed on the metal surface. This process, called metal runoff, contributes for zinc dispersion in soils and waters. In order to make accurate estimation of zinc runoff induced by atmosphere in humid tropical climate, samples of pure Zn and hot dip galvanized steel have been exposed in the Gulf of Mexico. The data reveal that this process is strongly influenced by factors which determine the aggressivity of the environment (pluvial precipitations, cycles of dry and rainy periods, atmospheric pollutants, air humidity). High annual rates of zinc runoff (6.5 -8.5 ± 0.30 g Zn m -2 yr -1 ) were released, being the runoff 63 -87% of the zinc corrosion rust. The zinc mass loss has been related to several independent parameters, presenting linear equation, which indicates the air contaminant SO 2 as the major factor controlling the runoff of zinc. The reported results show higher runoff of zinc samples, compared to that of hot dip galvanized steel.
TL;DR: In this article, the authors investigated the corrosion behavior of low alloy steel, in the presence of anaerobic sulfate-reducing Desulfotomaculum sp. which was isolated from an oil production well.
Abstract: In this study corrosion behavior of low alloy steel, in the presence of anaerobic sulfate-reducing Desulfotomaculum sp. which was isolated from an oil production well, was investigated. In order to determine corrosion rates and mechanisms, mass loss measurements and electrochemical polarization studies were performed without and with bacteria in the culture medium. Scanning electron microscopic observations and energy dispersive X-ray spectra (EDS) analysis were made on steel coupons.
The effect of iron concentration on corrosion behavior was determined by Tafel extrapolation method. In a sterile culture medium, as the FeSO4 · 7H2O concentration increased, corrosion potential (Ecor) values shifted towards more anodic potentials and corrosion current density (Icor) values increased considerably. After inoculation of sulfate-reducing bacteria (SRB), Ecor shifted towards cathodic values. Icor values increased with increasing incubation time for 10 and 100 mg/L concentrations of FeSO4 · 7H2O.
Results have shown that the corrosion activity changed due to several factors such as bacterial metabolites, ferrous sulfide, hydrogen sulfide, iron phosphide, and cathodic depolarization effect.
TL;DR: In this paper, the effect of sulfate reducing bacteria (SRB) on the hydrogen permeation rate through ferrite-pearlite and sorbite steels of quite similar chemical composition was studied using a specially designed facility.
Abstract: The effect of sulfate reducing bacteria (SRB) on the hydrogen permeation rate through ferrite-pearlite and sorbite steels of quite similar chemical composition was studied using a specially designed facility. Tests were carried out in synthetic sea water, sterile or inoculated with bacteria, at potentials corresponding to cathodic protection (- 800 mV ta -1400 mV NCE ). Cathodic polarization within the studied potential range did not stop the metabolism of SRB. Presence of SRB was found to increase the hydrogen permeation rate, to form S 2- ions, to increase the polarization current, to modify the impedance spectrum and to change the appearance of cathodic deposits in comparison with sterile conditions. The promoting effect of SRB on the hydrogen uptake was concluded to be the result of the increase in polarization current due to the formation of the less protective layer of cathodic deposits on the steel surface, the presence of S 2- ions and the possible decrease in pH. Despite the similar tendencies, the effect of SRB on hydrogen uptake was more pronounced in the case of sorbite steel. The bacteria action can cause hydrogen deterioration of steel at potentials, recognized as safe ones at cathodic protection.
TL;DR: In this article, X-ray tomography was used to analyse the areas, damaged by chloride induced corrosion, with dimensions of a few μm, which were verified by inspection of surfaces of the bars after removing the cover mortar.
Abstract: Within the scope of examinations at steel specimens embedded in chloride contaminated mortar for the first time X-ray tomography was used to analyse the areas, damaged by chloride induced corrosion. Damaged areas with dimensions of a few μm could be detected. The results from the X-ray tomography were verified by inspection of surfaces of the bars after removing the cover mortar.
TL;DR: In this article, the electrochemical kinetics results measured during the corrosion of API X52 pipeline steel immersed in aqueous environments, containing dissolved hydrogen sulfide (H 2 S) under turbulent flow conditions were presented.
Abstract: This work presents the electrochemical kinetics results measured during the corrosion of API X52 pipeline steel immersed in aqueous environments, containing dissolved hydrogen sulfide (H 2 S) under turbulent flow conditions. In order to control the turbulent flow conditions, a rotating cylinder electrode (RCE) was used. Five different rotation rates were studied: 0 (or static conditions), 1000, 3000, 5000 and 7000 rpm. It was found that the turbulent flow increases the corrosion rate and the corrosion mechanism for X52 steel exhibits a significant dependence on mass transfer on the cathodic kinetics.