In the present work, the AZ61 alloy, one of the most important commercial structural magnesium alloys, was anodized in three different alkaline electrolytes consisting of 3 M KOH + 0.15 M Na2SiO3 + 0.1 M Na2B4O7.10H2O, 3 M KOH + 0.5 M Na3PO4 and 3 M KOH + 0.50 M Na2SiO3. The treatment was conducted at two different current densities, 20 and 30 mA.cm-2 for 10 minutes. The anodized layers were characterized by scanning electron microscopy, X-ray diffractometry and X-ray photoelectron spectroscopy. The corrosion resistance was assessed by potentiodynamic polarization tests. The SCC behavior was studied using slow strain rate tests in 0.1 M NaCl solution at room temperature. Conventional tensile tests were also conducted in air. The susceptibility to SCC was dependent on the morphology of the anodized film. The composition of the electrolyte and the current density of the anodization treatment affected the SCC susceptibility of the AZ61 alloy. The best corrosion resistance and the lowest susceptibility to SCC were obtained for samples anodized in the borate-containing electrolyte at 30 mA.cm-2. The smooth and compact surface morphology of the anodized film obtained in this condition was the main reason for the improved SCC behavior of the AZ61 alloy.

The corrosion resistance of high entropy alloys was reviewed in the present work. The main focus was to explore the correlation between alloy composition, passive film stability and corrosion properties and use this information to develop a materials selection procedure based on the Ashby approach. Corrosion current densities and pitting potentials were the main design parameters used to rank different alloys, based on a careful examination of data published in the literature, considering uniform and localized corrosion, respectively. The outputs of the selection process clearly indicated a strong dependence of the corrosion resistance on passive film stability, although microstructural homogeneity and uniform distribution of alloying elements should not be disregarded. Proper combinations of elements such as Co, Al, Ti, Mo and Cr, especially, are effective at enhancing the corrosion resistance of high entropy alloys.

Abstract Aluminum alloys are the state-of-art materials for structural components of aircrafts. As they are susceptible to localized corrosion, this kind of damage can become a major threat for its safe use in aircraft components. Therefore, surface protection of aluminum alloys against corrosion is a core issue in these applications. In this work, an alternative eco-friendly cerium-based surface pretreatment was developed and applied on the AA1230 clad of the AA2024-T3 alloy for corrosion protection. The corrosion resistance evaluation of this modified surface was evaluated by several techniques. The results were compared to chromium based conventional treatments and revealed that the coating layer, composed of spherical nodular nanostructures of cerium, obtained with the proposed eco-friendly treatment, improved the corrosion resistance of the alloy. Moreover, it was comparable to the corrosion behavior of chromate-treated alloy, showing that this treatment is a promising alternative to replace chromate based surface treatments.

In this work, scanning electrochemical microscopy (SECM) was employed to study the corrosion behavior of anodized AZ31B magnesium alloy exposed to simulated body fluid. SECM measurements were carried out in surface generation/tip collection mode. The hydrogen evolution flux caused during corrosion of the magnesium alloy was oxidized at the ultra-microelectrode (UME). Thus, this experimental procedure allowed evaluating the effect of the anodic protection in this alloy from the SECM analysis of Z- approximation curves, cyclic voltammograms and topographic maps. The results evidence differences in the local electrochemical response of magnesium alloy in the anodized and pristine conditions. The main sites of H2 evolution were verified in the magnesium alloy without anodizing at short exposure times.

The aim of the present work was to investigate the effect of the treatment time on the surface chemistry and corrosion behavior of cerium-based chemical conversion coatings on the AZ91D magnesium alloy. The conversion coating was prepared by the immersion technique from a bath consisting of 0.05 mol.L-1 Ce(NO3)3.6H2O and 0.254 mol.L-1 H2O2 (30 wt.%) for times ranging from 20 s to 120 s. The surface chemistry was examined by X-ray photoelectron spectroscopy (XPS). The corrosion behavior was assessed by electrochemical impedance spectroscopy and potentiodynamic polarization. XPS analysis detected the presence of cerium oxides (Ce2O3 and CeO2) and cerium/magnesium hydroxides. The best corrosion behavior was observed for the treatment conducted for 60 s. The results are discussed with respect to coating morphology and composition.

The aim of the present work was to explore the correlation between the physical metallurgy of titanium alloys and its main attributes to select optimized materials for structural aircraft applications in the landing gear beam. The Ashby's method was employed as the materials selection strategy to consolidate and evaluate the data collected from the current literature in a comprehensive and consistent analysis. Landing gear beam materials are mainly β and near-β alloys. Considering the need for high specific strength and fatigue resistance, the best candidate among them was Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe alloy. Finally, a brief discussion of additional aspects related to alloy design, microstructural features and their influence on the mechanical properties is presented.

Ternary Ni-W-P films were produced by electroless deposition using baths with different tungsten concentrations. After deposition, the coated surfaces were annealed at 400°C for 1h. Surface morphology and film composition in the as-plated condition were assessed by SEM and EDS analyses, respectively. The crystalline phases after annealing were investigated by X-ray diffraction (XRD). Nanoindentation tests were performed to assess the mechanical properties of the deposited films. Surface roughness was determined by confocal laser scanning microscopy (CLSM). Friction coefficient was evaluated by reciprocating were tests in a nanotribometer. The corrosion behavior was evaluated by potentiodynamic polarization curves. The results showed that the surface morphology, crystallization behavior and corrosion resistance were affected by the tungsten content in the film. The best corrosion performance was obtained for the ternary films after annealing. Hardness, surface roughness and friction coefficient were dependent of the tungsten concentration in the film.

The aim of the present work was to study the passive film stability and pitting corrosion behavior of the AISI 409 stainless steel. The electrochemical tests were carried out in 0.1 M NaCl solution at room temperature. The general electrochemical behavior was assessed using electrochemical impedance spectroscopy (EIS) measurements whereas the semiconducting properties of the passive film were evaluated by the Mott-Schottky approach. Pitting corrosion was investigated using potentiodynamic and potentiostatic polarization tests. Surface morphology was examined using confocal laser scanning microscopy and scanning electron microscopy (SEM). Energy dispersive X-ray spectroscopy (EDS) analyses were carried out to identify the composition of precipitates that could act as preferential sites for the onset of pitting corrosion. The results showed that the passive film presents n-type semiconductive behavior. Grain boundaries played an important role as pitting initiation sites for the AISI 409 stainless steel.

Pitting corrosion of the aluminium cladding of spent nuclear fuels stored in light water pools has been observed. To prevent this, coating of the Al cladding with hydrotalcite (HTC) was proposed. This paper presents the effect of chemical bath and processing parameters on microstructure and corrosion behavior of HTC coatings on alloy AA 6061 specimens. The HTC coating from the high temperature nitrate bath was homogeneous, thicker and consisted of well-defined intersecting platelets than that formed from the room temperature carbonate bath. Electrochemical polarization tests carried out with HTC coated AA 6061 specimens in 0.01 M NaCl revealed that specimens coated with HTC from the nitrate bath and further treated in a cerium salt solution were the most resistant to corrosion. Field tests in which un-coated and coated AA 6061 alloy coupons as well as full-size plates were exposed to the IEA-R1 reactor's spent fuel basin for duration of up to 14 months further corroborated the high corrosion resistance imparted by the high temperature HTC + Ce coating. The mechanism by which the HTC coating and cerium protect the Al alloy is discussed.

The resistance to localised corrosion of the full austenitic 15%Cr-15%Ni-1.2%Mo titanium stabilized stainless steel (DIN W. Nr. 1.4970) was investigated by electrochemical methods including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and potentiostatic polarization measurements in a phosphate-buffered solution (PBS). The low carbon and non-stabilized austenitic stainless steel, AISI 316L (ASTM F-138), widely used for surgical implants, was also tested for comparison. The tests were conducted at room temperature after a stable potential had been reached. After the electrochemical measurements, the surfaces of the specimens were observed using SEM to evaluate the presence of pits. Potentiodynamic polarization results showed that both steels are prone to localized corrosion. Larger pits were found on the surface of AISI 316L specimens after the electrochemical tests. EIS response has indicated the duplex structure of the passive oxides. The results showed that the electrochemical behaviour of the DIN W. Nr. 1.4970 is better than of AISI 316L steel. Therefore, their application as an implant material may be considered.

The corrosion products of carbon steel and weathering steel exposed to three different types of atmospheres, at times ranging from one to three months, have been identified. The steels were exposed in an industrial site, an urban site (São Paulo City, Brazil), and a humid site. The effect of the steel type on the corrosion products formed in the early stages of atmospheric corrosion has been evaluated. The corrosion products formed at the various exposure locations were characterized by Raman microscopy, X-Ray diffraction (XRD) and their morphology was observed by Scanning Electron Microscopy (SEM). Three regions of different colours (yellow, black and red) have been identified over the steel coupons by Raman microscopy. Analysis carried out on each of these areas led to the characterization of the correspondent oxide/hydroxide phases. The main phases present were lepidocrocite (g-FeOOH) and goethite (a-FeOOH). Small amounts of magnetite (Fe3O4) were also eventually encountered.