(CoCrFeNi) 1−x Mo x thin films with various Mo content (0–10 at.%) were grown by magnetron sputtering on a stainless steel substrate. The films with 0–2 at.% presented two crystal structures: one FCC ...phase and one sigma phase, while films with higher Mo content only had the FCC structure. All films have a (111) texture and follow the topography of the substrate. The corrosion resistance of the films was evaluated in 0.05 M H 2 SO 4 at room temperature and at 80 °C. It was observed that the corrosion current densities considerably decreased for Mo > 2 at%, and that the current densities were higher at the elevated temperature. Scanning Kelvin Probe Force Microscopy showed a large potential difference between the main FCC phase and sigma phase for the Mo0–2 films. This would suggest that preferential dissolution of the FCC phase occurs over the sigma and reduces the corrosion resistance. Such preferential dissolution does not occur for the higher Mo content films with only the FCC phase. The high corrosion resistance was also attributed to the inhibition of Fe and Cr dissolution by Mo and the stabilisation of the Cr enriched oxide by incorporating Mo oxides into the passive film, identified by X-ray photoelectron spectroscopy. The low corrosion current densities (below 1 µA/cm 2 ) make these thin films possible candidates for protective coatings of bipolar plates in PEM fuel cells.
In many industrial applications, metallic materials are exposed to harsh operating conditions. Due to a combination of chemical and thermal stresses, the constructional and functional materials are ...degraded, and their utility properties are lost. These undesirable events are of a physicochemical nature and are commonly known as ‘corrosion’. In this Special Issue Book, 3 reviews and 18 original research papers focused on the complex relationships between the microstructure, phase constitution, and corrosion behavior of metallic materials are collected. Both high temperature and low temperature corrosion studies are included as they investigate the physicochemical processes at the material interfaces. Furthermore, possibilities for increasing the corrosion resistance of metallic materials are studied by means of surface modification and application of protective layers. This Special Issue Book, Microstructure and Corrosion Behavior of Advanced Alloys, displays the diversity and complexity of modern corrosion research. It is hoped that it will become a valuable source of reference for corrosion scientists.
This book contains thirty articles on various topics related to the corrosion and protection of metallic materials. This topic is of strong actuality both due to the aging of plants and ...infrastructures that require checks and maintenance, and to the use of traditional materials in increasingly aggressive environments, added to the need of changing the current anti-corrosion systems with less environmental impact methods. Finally, the new development of innovative materials, such as additive manufacturing or high-entropy alloys, needs the characterization of their corrosion behavior. In this issue, there are works on new alloys obtained for additive manufacturing or high entropy, on the study of corrosion and stress corrosion cracking and hydrogen embrittlement mechanisms, through electrochemical and microscopical techniques, studies on low environmental impact inhibitors and biocides, as well as ceramic and metal protective coatings. Finally, there are works on the study of the residual mechanical resistance of corroded infrastructures and on monitoring and non-destructive control. In this way, the book therefore offers a somewhat varied panorama of research trends in the field.
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•A comparatively considerable corrosion resistance is achieved in extruded Mg-3Zn-11Gd-0.6Zr alloy.•Lower potential differences between Mg-Zn-Gd ternary phases and Mg matrix are ...beneficial to corrosion behavior.•A wide distribution of compact X-phase lamella acts as corrosion barrier during corrosion.•X-phase could act as an anode during micro-galvanic corrosion with W-phase.
The corrosion behavior and mechanism of as-cast and as-extruded Mg-Zn-Gd-Zr alloys with specific ternary phases are investigated using scanning electron microscope (SEM), scanning Kelvin probe force microscope (SKPFM), immersion and electrochemical tests. Lamellar X-Mg12GdZn, net-like W-Mg3Gd2Zn3 and strip-like I-Mg3Zn6Gd phases form successively. The eutectic W-phase owns the highest potential difference of 120 mV with Mg matrix, accelerating micro-galvanic corrosion. Continuously distributed and undersized I-phase leads to uniform corrosion. The as-extruded Mg-3Zn-11Gd-0.6 Zr alloy exhibits superior corrosion resistance, due to the relatively low potential difference between X-phase and matrix, the corrosion barrier effect and typical {0002} <10−10> texture components.
Titanium and its alloys show outstanding application prospects in many industrial fields due to their high specific strength, good corrosion resistance, high temperature resistance, etc. However, at ...present the corrosion failure of Ti alloys is attracted great attention with gradual increasing applications. The different localized corrosion forms are introduced in this review, including galvanic corrosion, crevice corrosion, pitting corrosion, hydrogen-induced cracking, stress corrosion crack, microbiological corrosion, corrosion fatigue, and corrosion wear. Among them, the corrosion failure caused by stress corrosion crack and hydrogen-induced cracking is the most serious, accounting for about 40–60% of the actual failure accidents. The effects of temperature, pressure, corrosive media and microstructure on the failure of titanium alloys are discussed. Particularly noteworthy, F
is extremely aggressive to the passive film of titanium alloys. The corrosion behavior of titanium alloys applied in aerospace, marine, petrochemical industries and biomedical environments are introduced. In the above environments, the passive film is most easily damaged and difficult to passive in high temperature and oxygen-deficient environments. The current controversies in the corrosion mechanism have also been proposed, especially the stress corrosion that has the most serious impact on titanium alloys, and its mechanism will be the focus of future research.
In order to study the effect of defects on the corrosion behavior of MAO coatings, global electrochemical method including potentiodynamic polarization (PDP) and electrochemical impedance ...spectroscopy (EIS) was used to measure the corrosion resistance of MAO coatings. Local electrochemical measurements including local impedance spectroscopy (LEIS) and scanning vibrating electrode technique (SVET) were used to study the local corrosion mechanism. The confocal microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to observe the microstructure and phases of the samples. Results of global electrochemical measurement demonstrate that the scratches cause the reduction of the impedance and the increase of the corrosion current density. LEIS results show the impedance value distribution of the coating with the scratch. With the changes over time, the minimum impedance value of the scratch decreases first and then increases from the third hour. SVET results show the corrosion current density distribution of the scratched coating. The maximum corrosion current density at the scratch increases first and then decreases. The results of local electrochemical measurements show that the corrosion rate at the scratch decreases when the reaction lasted 3 h. Confocal microscopy found that the scratch is expanding with increasing time, and the depth and cross-sectional area of the coating is 5 times deeper and 10 times larger than that of 7075Al with scratch at the first 6 h. The 6-day immersion test proved that the scratch coating still has the protective effect on the substrate. The main corrosion product is Al(OH)3. A physical model reflecting the mechanism of the scratch propagation and the formation of the corrosion product film is proposed.
•Global and local electrochemical corrosion of scratched MAO coating on Al Alloy was studied.•The electrochemical impedance and current distribution of scratches were analyzed by LEIS and SVET.•A phenomenological model for the influence of scratch on the local corrosion of the MAO coated Al alloy was proposed.
Graphene has long been considered a superlative protection material due to its extraordinary characteristics and properties. However, its high electrical conductivity can facilitate the ...electrochemical corrosion of metal, which strongly limits its anti-corrosion applications. Here, we developed a facile fluorination strategy to suppress the corrosion promotion activity of graphene. Fluorinated reduced graphene oxide (FrGO) exhibited low electrical conductivity (3.643 × 10−13 S/cm), which proved unable to trigger micro-galvanic corrosion. Furthermore, acridizinium ionic liquid (IL) MAcBr was noncovalently grafted on FrGO to achieve the well dispersion in the polymer matrix. Results revealed that FrGO-IL nanohybrid can be stably dispersed in the epoxy resin. Electrochemical impedance spectroscopy revealed that incorporating a small percentage of FrGO-IL into waterborne epoxy matrix effectively improved the corrosion resistance performance of the coating by exerting the superior shielding effect and inhibiting the ability for micro-galvanic corrosion. Moreover, local electrochemical and scratching tests further confirmed that FrGO-IL significantly reinforced the corrosion protection capability of waterborne epoxy coating because the well-dispersed nanohybrid enhanced the integrity of the composite coating, effectively utilizing the labyrinth effect. Our finding could inspire the development of new graphene-based materials with superior protection properties for metal materials.
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•Field exposure tests in Maldives are performed to compare the CPFs of 3Ni WS and conventional WS.•CPF of 3Ni WS presents superiority in structure, phase and elemental distribution, and ...electrochemical properties.•The elemental Ni in CPF is enriched mainly in the inner layer in the form of NiFe2O4.•NiFe2O4 refines the crystal phases, transforms γ-FeOOH to nanophase α-FeOOH, and produces an electronegative inner layer.
Corrosion product film (CPF) formation and its beneficial effect on corrosion protection of a Ni advanced weathering steel (WS), 3Ni WS, was investigated under the harsh marine environment in Maldives. The influence of Ni on the structure and the corrosion resistance mechanism of CPF was in detail studied. The CPF of 3Ni WS exhibits superiority in physical structure, phase composition, elemental distribution, and electrochemical properties over that of the conventional WS studied. These advantages are attributed to the formation and aggregation of NiFe2O4 in the inner layer of the CPF, which refines the crystal phases, transforms γ-FeOOH to fine-grained α-FeOOH, and forms an electronegative inner layer to resist Cl.
In this study, the use of electrical resistance (ER) sensors to monitor the corrosion of Al94Cu6 alloy is assessed and compared with 2024‐T3 coupons. Under uniform corrosion, a good correlation was ...found between the ER sensors and mass loss on coupons. Three different chloride depositions are studied: (i) pre‐contamination with dry/wet cycles, (ii) Volvo standard accelerated corrosion test and (iii) neutral salt spray test. The obtained results show good reproducibility of the ER sensors under all tested conditions. This suggests that ER sensors more levelled the effect of localised corrosion through a large surface evaluation compared with cross‐sections. The corrosion thickness obtained with the ER sensors does not correspond to the mean depth obtained by cross‐sections. This can be explained by the distribution and size of the localised corrosion events according to a finite element model proposed. The ER method allows obtaining useful real‐time corrosion data for the understanding of the corrosion mechanisms and the development of accelerated tests. The chloride concentration, the frequency of salt application and wet/dry cycles have a strong influence on the corrosion rate of aluminium alloys.
Electrical resistance (ER) aluminium (AlCu) sensors and 2024‐T3 coupons are exposed under chloride‐contaminated atmospheric conditions. ER corrosion thickness obtained appears (i) well reproducible, (ii) different from corrosion depth by cross‐section and (iii) relevant to provide real‐time corrosion data. ER sensor behaviour is explained by a simple finite element modelling considering the pit size, geometry and surface density.
To investigate the effect of atmospheric corrosion on the fatigue properties of 2024-T4 aluminum alloy structures during the whole corrosion period, atmospheric and accelerated pre-corrosion fatigue ...tests were carried out. Field exposure tests were carried out for 7, 12, and 20 years. A laboratory accelerated corrosion test method was proposed to simulate the whole atmospheric corrosion period from initial pitting to the subsequent exfoliation corrosion, and the reliability was verified through an analysis of the corrosion morphology, corrosion products, and thickness variation. Pitting and intergranular corrosion occurred after a short exposure to atmospheric corrosion, and intergranular corrosion was the dominant corrosion damage mode. The fatigue cracks initiated at the deepest boundary of intergranular corrosion. The fatigue life decreased dramatically during the initial stage of atmospheric corrosion and then decreased more slowly. Finally, the mechanism through which atmospheric corrosion affected the fatigue properties was analyzed.
•An accelerated corrosion method was proposed to simulate the atmospheric corrosion.•The fatigue cracks initiated at the deepest boundary of IGC.•Fatigue life decreased sharply during the initial stage, and then decreased slowly.•The mechanism of atmospheric corrosion affecting the fatigue property was proposed.•The non-uniform atmospheric corrosion at initial stage affected fracture locations.
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