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In this work, the corrosion susceptibility of powder coated Al6060 alloys with increasing Cu and Zn content is evaluated in a benchmark test. Although higher Cu and Zn limits would enable the industry to increase the use of end-of-life scrap and thus produce eco-friendlier aluminium profiles, such alloys are often disregarded due to concerns of corrosion, especially filiform corrosion. Our results suggest that this concern is ungrounded as long as typical quality specifications for the pre-treatment and coating process are followed and the alloy composition is kept within the limits of the European norm AW6060. Furthermore, we point out that the variation of the results due to processing at different coating production lines is larger than the difference between alloys of different Cu and Zn contents.

The effect of hot stamping on the corrosion properties of boron-manganese 22MnB5 steel coated with hot-dip aluminum-silicon was evaluated under severe conditions by a continuous salt spray test (SST). The corrosion mechanism changed from localized to generalized, as cathodic precipitates were not present after hot stamping. Intrinsic defects in press-hardened steel samples were the reason for severe damage in both metallic coating and steel substrate under SST conditions. The red rust formed at the top surface, characterized as different iron-based compounds, is due to both the iron diffusion from the steel substrate toward the surface and the corrosion of the steel substrate.

This work analyses the microstructural defects and the corrosion behaviour of 316L stainless steel clads deposited by laser metal deposition on wrought conventional material, which is a highly relevant system for repair applications. The different defects and microstructural features found in these systems were identified and analysed from a perspective relevant to the corrosion performance of these materials. The role of these features and defects on the corrosion process was evaluated by exposure of the samples to corrosive media and further examination of the corrosion morphology. The heat-affected zone, located on the wrought base material in close vicinity of the deposited clad, was identified to be the primary contributor to the corrosion activity of the system due to the large depletion of alloying elements in this region, which significantly decreased its pitting resistance. Alongside the heat-affected zones, relatively small (

Metal additive manufacturing (AM) refers to any process of making 3D metal parts layer-upon layer via the interaction between a heating source and feeding material from a digital design model. The rapid heating and cooling attributes inherent to such an AM process result in het erogeneous microstructures and the accumulation of internal stresses. Post-processing heat treatment is often needed to modify the microstructure and/or alleviate residual stresses to achieve properties comparable or superior to those of the conventionally manufactured (CM) counterparts. However, the optimal heat treatment conditions remain to be defined for the ma jority of AM alloys and are becoming another topical issue of AM research due to its industrial importance. Existing heat treatment standards for CM metals and alloys are not specifically designed for AM parts and may differ in many cases depending on the initial microstructures and desired properties for specific applications. The purpose of this paper is to critically review current knowledge and discuss the influence of post-AM heat treatment on microstructure, me chanical properties, and corrosion behavior of the major categories of AM metals including steel, Ni-based superalloys, Al alloys, Ti alloys, and high entropy alloys. This review clarifies significant differences between heat treating AM metals and their CM counterparts. The major sources of differences include microstructural heterogeneity, internal defects, and residual stresses. Under standing the influence of such differences will benefit industry by achieving AM metals with consistent and superior balanced performance compared to as-built AM and CM metals.

Stress corrosion cracking (SCC) behaviour of L-PBF processed alloy 718 in chloride-containing solution was revealed, utilizing the microcapillary method under constant tensile loading. Results were compared with conventionally produced counterparts. Passive layer resistance was compared quantitatively by implementing electrochemical polarization experiments, in as-received and under tensile loading states. Superior corrosion and SCC resistance of L-PBF specimens under tensile loading were identified. Submicron cracks were initiated adjacent to the subgrain boundaries and the underlying mechanisms were elucidated as the synergistic effect of various microstructural factors.

The AA3003 alloy is widely used as fin material in heat exchangers. The lifetime of these heat exchangers is mostly determined by their corrosion properties. Twin roll casting (TRC) of AA3003 material is known to often result in the formation of a macrosegregation area of alloying elements toward the center plane of the casted strip (center line segregation = CLS). Considering the potential exposure of cross-sectional areas of TRC material in the heat exchanger fin application, and the relatively high corrosion susceptibility of the CLS, the study of this region is of key importance to understand the microstructural effects on the resulting corrosion mechanisms and kinetics for these materials. Typically the alloys are homogenized to bring the microstructures closer to an equilibrium state, but the impact of this heat treatment on the corrosion properties is insufficiently studied. Therefore, this study investigates the effect of different homogenization procedures on the corrosion properties of the CLS and the interaction of the intermetallic particles with the surrounding aluminum matrix. This work shows that the pitting corrosion resistance is greatly dependent on the homogenization temperature, with better corrosion resistance obtained with higher temperature, especially near the CLS. This difference in corrosion behavior is completely attributed to a difference in microstructure and not to an oxide layer effect. Furthermore, it is observed that not only temperature will have a large influence on the corrosion resistance, but duration of the heat treatment as well.

The reliability of printed circuit boards (PCB) is at risk due to continuous miniaturization. As a result, PCBs are more susceptible to external factors such as humidity, temperature, contamination, etc., which affect their general performance, leading to failure of electronic devices. Therefore, protection of the devices against these factors is gaining greatly in importance. Plasma polymerization is used as a method to form a protective barrier by applying plasma polymer films on PCBs. However, the humidity robustness of such plasma coatings on the PCB surface is unknown. In this work, several methods were used to characterize two types of plasma-coated PCBs based on 1H,1H,2H-perfluorodecyl acrylate precursor (single-layer and stacked coatings) upon exposure to humidity, temperature, and bias voltage. Modulated-temperature differential scanning calorimetry enabled thermal analysis of the plasma coatings. Electrochemical impedance spectroscopy in combination with the gravimetric moisture vapor sorption technique were used to study the interaction of these coatings with moisture and quantify the water uptake. The results revealed an only 2% increase of the capacitance of the coatings due to water uptake. Direct-current (DC) leakage current measurements were used to study the influence of a bias voltage applied between the electrodes on the coated PCBs upon exposure to cyclic climatic conditions. Electrical DC testing revealed the protective character of the stacked coating, which did not fail under the given stress conditions, in contrast to the single-layer plasma coatings.

Aluminum alloy (AA) 3003 is widely used as fin and tube material in heat exchangers. In these heat exchangers, the tube and fin material are brazed together by means of an AA4xxx alloy. In this study, the effect of a simulated brazing step on the microstructure and corrosion behavior of a twin roll casted (TRC) AA3003 was studied. In particular, the effect of simulated brazing on the corrosion properties of the centre line segregation (CLS) of alloying elements and the interaction of the intermetallic particles with the surrounding matrix is explored. It is shown that the cross sections are significantly more active than the surface of the TRC AA3003, revealing the importance of the CLS on the corrosion behavior. Furthermore, it is shown that the number of pits and their depths decreased considerably on the exposed cross sections after simulated brazing, especially near the CLS. Scanning Kelvin probe force microscopy measurements show that after the simulated brazing step the Volta potential difference between the intermetallic particles and the matrix reduced significantly. This change in the Volta potential could be caused by the slight increase of Si content in the matrix.

The Zinc level in many 6000 Al alloys (Al-Mg-Si-type) was set to a maximum of 0.03 wt% as common industrial practice. Concentrations above 0.03 wt% can modify the alkaline etching mechanism causing the surface to go from a desired smooth look associated with a grain boundary attack (GBA), into an undesired speckled appearance due to preferential grain etching (PGE), visible after anodizing. This significantly limits the ambition of reducing the carbon footprint of Aluminum by increasing the amount of recycled material in the production process. Because Cu has been reported to counteract this negative effect of Zn, the present study is dedicated to contribute to the understanding of this interaction and is focused on Zn and Cu in peak aged AlMgSi alloys. The chemical composition of the various precipitates formed in two Al6063 alloys was studied by means of TEM and EDX, whereby Zn was found in the Q phase (AlMgSiCu) grain boundary precipitates. Two alloys, with different content of Cu and Zn were studied. The Zn/Cu ratio in the bulk was similar for both alloys, but the level of Zn in the Cu containing Q particles in the grain boundaries was different. The increased Zn concentration in Q phase precipitates is believed to decrease the potential of the precipitates with respect to the surrounding matrix. Thus, the Cu/Zn ratio in these alloys is extremely important as it defines the potential differences that in turn cause either GBA or PGE., SCOPUS: ar.j, info:eu-repo/semantics/published

The occurrence of preferential grain etching (PGE) during alkaline etching of aluminum extrusion alloys from the 6XXX series is often linked to the presence of certain impurity elements such as zinc, causing an undesired etching appearance. In the presented work, an additional culprit in this context is identified, which has not been investigated yet. A clear relation between PGE and the presence of a subsurface shear layer is identified for extruded Al 6060 alloys containing 0.02 and 0.06 wt% Zn. This shear layer can be distinguished from the bulk of the metal by its difference in crystallographic texture as visualized by electron backscatter diffraction (EBSD). For the Zn enriched alloy, the //ND grains are etched away faster than grains with other orientations, resulting in the grainy appearance typical for PGE. Independent of the Zn content in the alloy, once the shear layer is removed and //ND grains are practically absent on the new surface, the depths variations caused by preferential etchingdisappear. Instead, the surface of the alloy is attacked uniformly by the caustic etch bath.

For the corrosion protection of steel rebars in concrete, five different molybdate-phosphate conversion coatings were prepared, by changing the molybdate-phosphate ratio in the conversion baths. Their composition and morphology were studied with GD-OES, XPS, Raman spectroscopy and SEM-EDX and a schematic representation of their structure is suggested. Further, the corrosion resistance properties of the coatings were evaluated in a simulated concrete pore solution (CPS) containing chlorides, using anodic polarization measurements. Thanks to the elaborated surface analysis their corrosion behaviour could be correlated to their structure. The results show that by altering the molybdate-phosphate ratio the structure and, consequently, the corrosion protection properties change significantly. By optimizing this ratio a twofold protection mechanism could be attained, demonstrating both good barrier properties and consistent with active corrosion protection.

Sr is known to transform the morphology of the eutectic silicon phase as well as the Fe-rich β phase in Al-Si alloys, improving their mechanical properties. However, little is known about the effect Sr has on the (local) corrosion properties of aluminium alloys. This study investigates the effect of Sr addition to a modified AA3003 heat exchanger material on the morphology of the different phases present, especially the Fe-rich phases, as well as on the (local) corrosion properties of this material. This work reports the formation of a Sr-rich phase, which slightly increases the macrohardness of the material. The Fe-rich phases are not shown to be refined/influenced by the addition of Sr Potentiodynamic polarization experiments showed an increase in pitting potential by increasing the amount of Sr in the material up to 0.4 wt.%. Nevertheless, the analysis of the corrosion morphology revealed that the Sr-containing particles did not contribute to the corrosion process despite their cathodic behaviour compared to the Al matrix as measured by Scanning Kelvin Probe Force Microscopy. This behaviour was attributed to the thicker oxide layer found on the Sr-rich particles.

This work studies the passive behavior and growth kinetics of the native oxide on additively manufactured AlSi10Mg and compares it with that of the conventional cast alloy, which presents a markedly different microstructure. With the use of a scanning Kelvin probe force microscopy (SKPFM)-based methodology, the growth kinetics of native oxide films on these alloys was examined. The microstructure of these materials had a great impact on the oxide growth and thickness, and consequently on its passive behavior. The native oxide on the additively manufactured sample presented faster growth and superior passive behavior than those of the cast alloy.

Press-hardened steels are commonly protected with hot-dip Al-Si coating. Due to the electrochemical complexity of this system, either before or after hot-stamping process, SKPFM was used to investigate the influence of the thermo-mechanical process on the electrochemical behaviour of the galvanic coupling. The hot-stamping process changed significantly the anodic/cathodic coupling of the coating/steel due to iron enrichment in the coating layer. Hence, a concurrent mechanism was thoroughly established, i.e., while the press hardening enhances the corrosion properties of the steel system (steel and metallic coating) through diffusion, at the same time it diminishes the cathodic protection of the Al-Si layer.

In this work, the effect of heat treatments on the anodizing behavior of additive manufactured AlSi10Mg material is studied. Specimens are subjected to artificial aging or stress release heat treatments, followed by galvanostatic anodizing in sulfuric acid. Optical and scanning electron microscopy are employed to study the microstructure and the oxide layer characteristics. Upon applying the heat treatments, the microstructure shows a gradual evolution from a continuous 3D silicon network toward separate coarse silicon particles in an aluminum matrix. The morphology of the silicon phase is found to be a deciding factor as it determines the fraction of silicon that is oxidized during anodizing. This in turn is found to have a direct impact on the anodizing efficiency and oxide layer uniformity. Thicker and more uniform oxide layers are obtained for the additive manufacture AlSi10Mg specimens after the silicon network is broken up due to the heat treatments.

This work analyzes the galvanostatic anodizing behavior of additive manufactured (AM) Al-Si alloys. Two main factors were studied here: 1) the influence of Si content on the anodizing behavior and on the porous structure of the anodic oxide film, and 2) the effect of pre-existing internal pores on the anodizing behavior of these materials. Three different alloys were anodized in H2SO4 electrolyte, with 7%, 10%, and 12% Si. The voltage responses of the different samples during anodizing were compared and the formed oxide was analyzed. The amount of Si in the AM Al-Si alloys was found to have a great influence on the anodizing voltage and consequently on the porous structure of the anodic oxide layer. However, the anodic oxide growth rate was nearly independent of the Si content in the samples. Moreover, the effect of internal porosity resulting from the metal additive manufacturing process on the anodizing behavior of these specimens was also analyzed. An outer anodic oxide layer decorated the pre-existing internal pores that were reached by the anodic oxide front. These internal pores were also characterized by the systematic appearance of cracks resulting from the volume expansion of anodic oxide layers advancing in opposite directions.

This work addresses the effect of deformation twinning on the dissolution corrosion behaviour of 316 L austenitic stainless steels in contact with static liquid lead-bismuth eutectic (LBE). For this purpose, plastically deformed 316 L steel specimens with distinctly different deformation twin densities were simultaneously exposed to oxygen-poor (

Additively manufactured (AM) AlSi10Mg is one of the most studied AM aluminium alloys to date. While several studies have focused on investigating its mechanical properties and corrosion performance, very little work has been dedicated to study corrosion protection mechanisms and surface treatments applicable for this material. This work presents for the first time an analysis of the mechanism of Zr electrochemical conversion on AM AlSi10Mg parts. A comparison with the conventional cast alloy was also conducted. An analysis of the specimens using SEM/EDS provided interesting insights concerning the effect of the microstructure on the deposition of the Zr conversion layer. This work demonstrates that due to the very fine microstructure and distribution of alloying elements in AM AlSi10Mg, a homogeneous deposition of the Zr conversion layer is promoted. Conversely, the cast alloy is characterized by a very heterogeneous deposition of the Zr conversion layer due to the presence of relatively large Fe-containing intermetallic particles. The influence of the conversion coating on the corrosion performance of these materials was also studied. The results show that while the conversion treatment has no impact on the corrosion resistance of the cast alloy, it greatly improves the passivity of the AM AlSi10Mg samples.

In this work, the role of the Si phase microstructure in the anodizing behavior of Al-Si alloys is studied. Experiments were conducted using an additive manufactured (AM) Al-Si10-Mg specimen and a cast alloy of approximately the same chemical composition. A systematic characterization of the anodic oxide film was conducted using a variety of surface analysis techniques. Clear evidence is provided through X-ray photoelectron spectroscopy analysis for the almost entire oxidation of Si during the anodizing of the additive manufactured specimens, which can explain the lower anodizing efficiency observed in the AM material compared to the cast alloy. Additionally, a more detailed characterization of the oxide layer revealed that a slightly thinner anodic oxide film is formed at the borders of the characteristic melting tracks resulting from the metal additive manufacturing process. Furthermore, the features observed in the voltage–time response during the anodizing of the AM specimens seem to be closely associated with the dimensions of the Al/Si cells present in the plane parallel to the direction of the oxide front growth.

Using a light optical microscope (LOM), microstructural analysis is carried out on plain-carbon, DP600, and As-Quenched (As-Q) martensitic steels to identify the different phases interacting with hydrogen. Our recently developed electrochemical procedure, based on cyclic voltammetry (CV) and potentiostatic discharging method, is applied on these steel alloys having different phases to monitor H-uptake in the steels with respect to their microstructural features. The electrochemical method is capable of measuring diffusible H-concentration (including mobile hydrogen) for the steel alloys under H-charging condition, where hydrogen embrittlement phenomena can occur within in-service environments. The best practice in this procedure is to perform electrochemical H-measurements immediately after H-charging without interruption between steps to avoid spontaneous H-loss. Various charging times are investigated to estimate the time to near H-saturation for each steel alloy. To gain additional insights in our H-related findings, hot extraction measurements are performed to measure the diffusible H-concentration in the steels. A clear correlation between the results of hot extraction and electrochemical discharging methods is confirmed by a mathematical model, based on Fick’s Law, predicting diffusible H-loss due to the time lag. Thus, under the used charging conditions, As-Q martensitic steel has been found to contain the lowest amount of diffusible hydrogen, with its near H-saturation reached after 4 hours of H-charging. DP600 is H-saturated after one hour of charging, while near H-saturation for plain-carbon steel is attained after 30 minutes. The fraction of mobile-H in plain-carbon steel is relatively higher than in DP600 steel.

Two types of self-repairing coatings for the protection of Al and its alloys are reviewed: (1) organic coatings with capsules containing repairing agent and (2) porous anodic oxide films with inhibitor solution stored in the pores of the oxide film. First, polyurethane microcapsules containing liquid surface-repairing agents were synthesized and polyurethane coating with the capsules was painted on Al alloy specimens. After mechanical damage to the coating, self-repairing occurred by the reaction of water vapor in the air with the repairing agents released from the capsules. Second, porous-type anodic oxide films were formed on Al alloys, and the pores of the anodic oxide films were filled with inhibitor solutions, followed by application of a covering polyurethane layer. Inhibitors released from the pores efficiently protected the Al alloy substrate from corrosion arising from induced mechanical damage.

This study addresses the effect of plastic deformation on the dissolution corrosion behavior of a Type 316L austenitic stainless steel. Dissolution corrosion was promoted by low oxygen conditions in liquid lead-bismuth eutectic (LBE). Specimens with controlled degree of plastic deformation (20%, 40%, and 60%) and a non-deformed, solution-annealed specimen were simultaneously exposed for 1,000 h at 500°C to static LBE with low oxygen concentration ([O] < 10−11 mass%). The corroded specimens were analyzed by various material characterization techniques. All exposed specimens exhibited dissolution corrosion. The non-deformed steel showed the least dissolution attack (maximum depth: 36 μm), while the severity of attack increased with the degree of steel deformation (maximum depth in the 60% steel: 96 μm). It was, thus, concluded that increasing the amount of plastic deformation in a Type 316L stainless steel results in higher dissolution corrosion damages for steels exposed to low oxygen LBE conditions. Addit...

When aiming for an increased and more sustainable use of metals a thorough knowledge of the corrosion phenomenon as function of the local metal microstructure is of crucial importance. In this work, we summarize the information presented in our previous publications[1-3] and present an overview of the different local (electrochemical) techniques that have been proven to be effective in studying the relation between different microstructural variables and their different electrochemical behavior. Atomic force microscopy (AFM)[1], scanning electrochemical microscopy (SECM)[2], and electrochemical scanning tunneling microscopy (EC-STM)[3] were used in combination with electron backscatter diffraction (EBSD). Consequently, correlations could be identified between the grain orientation and grain boundary characteristics, on the one hand, and the electrochemical behavior on the other hand. The grain orientation itself has an influence on the corrosion, and the orientation of the neighboring grains also seems to play a decisive role in the dissolution rate. With respect to intergranular corrosion, only coherent twin boundaries seem to be resistant.

The Al-Mn-Fe-Si alloy systems, produced via Twin Roll Casting (TRC), are mostly used in applications where a good corrosion resistance is required like brazing applications, for example heat exchanger systems in vehicles. While the TRC manufacturing method allows for a high production rate, it can cause some complications for the microstructure, such as centre line segregation (CLS). This CLS is the chemical segregation of the alloying elements occurring at the centre plane of the thickness and readily has an influence on corrosion characteristics of the materials. In this work the effect of a brazing step on the microstructure and corrosion behaviour of a TRC Al-Mn-Fe-Si alloy system was studied. Moreover, the effect of brazing on the corrosion properties of the centre line segregation of alloying elements (CLS) and the interaction of the intermetallic particles with the surrounding matrix was studied. In this study optical microscopy, SEM/EDS (scanning electron microscopy/ energy dispersive spectroscopy), HAADF-STEM/EDS (high-angle annular dark field-scanning transmission electron microscopy/ energy dispersive spectroscopy), AFM/SKPFM (atomic force microscopy/ scanning Kelvin probe force microscopy), potentiodynamic polarization and potentiostatic polarization were used to characterize the microstructure and corrosion behaviour. It was shown that the cross sections are significantly more active than the surface of the fin material, showing the importance of the CLS on the corrosion behaviour. Furthermore, it was shown that the pitting corrosion activity and penetration depth of the formed pits on the exposed cross sections decreased considerably after brazing, especially near the CLS. SKPFM measurements showed that after brazing the contact potential difference between the intermetallic particles and the matrix reduced significantly.

The microcapillary cell electrochemical method is capable of evaluating hydrogen (H) uptake in steel with respect to deformation, which is induced by various mechanical methods (cold rolling, bending and punching). A clear relation between the deformation degree and the local H-content is established for dual phase (DP600) steel. The magnitude of the deformation nearby a punched edge is quantitatively determined using electron backscatter diffraction technique. A shear-affected zone is identified at the edge of the punched hole. The dedicated local electrochemical measurements confirm the presence of high concentrations of local-H in this shear affected zone, which is likely detrimental for H-embrittlement.

This study focuses on the effect of heat treatments on the microstructure and corrosion behaviour of additive manufactured AlSi10Mg specimens. Non heat treated, artificially aged and stress released specimens were studied. The microstructure showed an evolution from cellular aluminium cells surrounded by a 3D network of fibrous eutectic silicon phase to coarse separated silicon particles. The corrosion behaviour was found to change with the heat treatments. Untreated and artificially aged specimens showed superficial corrosion attacks with microcrack formation while stress released specimens showed penetrating attacks without microcrack formation. Mechanisms were proposed for the microstructure evolution and the different corrosion behaviours.

Sodium molybdate is evaluated as corrosion inhibitor for steel in brackish water; it is encapsulated by interfacial polymerization and the produced capsules are characterized. Electrochemical impedance spectroscopy and corrosion potential measurements were used to determine the short-time corrosion inhibition while polarization curves were used for the estimation of the inhibition efficiency. The capsules composition, the Na 2 MoO 4 content and the release rate are then determined. Na 2 MoO 4 shows corrosion inhibition for at least 15 h. Capsules consist of polyurea and polyurethane which are formed due to the reaction of the isocyanates with the water of the emulsion and the used surfactants, respectively. Most of the inhibitor is released within 90 min. Electrochemical Impedance Spectroscopy and Scanning Vibrating Electrode Technique show corrosion inhibition on artificially damaged areas for the coatings containing the corrosion inhibitor capsules.

This work compares the microstructure and corrosion resistance of 316 L stainless steel samples prepared using two different additive manufacturing methods: selective laser melting (SLM), and laser metal deposition (LMD). A wrought material was used as reference. The specimens showed marked differences in their microstructure, as a result of the specific manufacturing conditions. All samples displayed similar corrosion potential and passive current density values. However, variations were seen in their potential passive range (SLM > LMD > Wrought). The wider passivity of the SLM specimen can be associated with its finer microstructure, which leads to a more stable native oxide.

Metal additive manufacturing (MAM), also known as metal 3D printing, is a rapidly growing industry based on the fabrication of complex metal parts with improved functionalities. During MAM, metal parts are produced in a layer by layer fashion using 3D computer-aided design models. The advantages of using this technology include the reduction of materials waste, high efficiency for small production runs, near net shape manufacturing, ease of change or revision of versions of a product, support of lattice structures, and rapid prototyping. Numerous metals and alloys can nowadays be processed by additive manufacturing techniques. Among them, Al-based alloys are of great interest in the automotive and aeronautic industry due to their relatively high strength and stiffness to weight ratio, good wear and corrosion resistance, and recycling potential. The special conditions associated with the MAM processes are known to produce in these materials a fine microstructure with unique directional growth features far from equilibrium. This distinctive microstructure, together with other special features and microstructural defects originating from the additive manufacturing process, is known to greatly influence the corrosion behaviour of these materials. Several works have already been conducted in this direction. However, several issues concerning the corrosion and corrosion protection of these materials are still not well understood. This work reviews the main studies to date investigating the corrosion aspects of additively manufactured aluminium alloys. It also provides a summary and outlook of relevant directions to be explored in future research.

This work evaluates the corrosion resistance of three Al-Si alloys processed by additive manufacturing (Al-Si7-Mg, Al-Si10-Mg, and Al-Si12) through a comparative analysis. It explores the influence of the silicon content on the microstructure and corrosion behavior of these alloys. An initial scanning electron microscopy analysis revealed that the silicon content in the samples affected the level of connectivity of the Si network, and this, consequently, influenced the formation of micro-cracks during corrosion. A model describing the evolution of the corrosion attacks and micro-cracks formation in the AM Al-Si alloys is proposed here.

This work presents a novel procedure to study the growth of the surface native oxide film on metals in air, based on scanning Kelvin probe force microscopy. For reactive metals such as aluminium, when the native metal oxide is damaged, fast reformation of the oxide film occurs. The methodology presented here allows this oxide film reformation to be studied in situ. By monitoring the evolution of the Volta potential with time in a scratch on the sample's surface, the characteristic behavior of the oxidation of aluminium metal could be observed. The procedure was carried out on a pure aluminium sample, but could potentially be applied in other metals, provided that the relation between the oxide film and the Volta potential is established. Keywords: SKPFM, Surface repassivation, Native oxide film

This work focuses on the effect of dissolved oxygen concentration in liquid lead-bismuth eutectic (LBE) on the onset of dissolution corrosion in a solution-annealed 316 L austenitic stainless steel. Specimens made of the same 316 L stainless steel heat were exposed for 1000 h at 450 °C to static liquid LBE with controlled concentrations of dissolved oxygen, i.e., 10−5, 10−6, and 10−7 mass%. The corroded 316 L steel specimens were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). A complete absence of dissolution corrosion was observed in the steel specimens exposed to liquid LBE with 10−5 and 10−6 mass% oxygen. In the same specimens, isolated “islands” of FeCr-containing oxides were also detected, indicating the localized onset of oxidation corrosion under these exposure conditions. On the other hand, dissolution corrosion with a maximum depth of 59 μm was detected in the steel specimen exposed to liquid LBE with 10−7 mass% oxygen. This suggests that the threshold oxygen concentration associated with the onset of dissolution corrosion in this 316 L steel heat lies between 10−6 and 10−7 mass% oxygen for the specific exposure conditions (i.e., 1000 h, 450 °C, static liquid LBE).

In a previous study, self-healing polyurethane coatings with microcapsules containing the high reactive liquid phase have been developed for the protection of metal from corrosion for long periods. In this study, we examine the effect of the amount of glycerol added in the microcapsule formation process on the shape of capsules and the self-healing ability of coatings with microcapsules. The capsule formation with large amounts of glycerol gave rise to clusters of capsules, while with small amounts of glycerol, the capsules were mainly independent ones. The selfhealing property of the coatings was more remarkable with decreasing the amount of glycerol in the capsule formation process.

Allyl methacrylate (AMA), methyl methacrylate (MMA), and propyl isobutyrate (PiB) are plasma deposited at ambient temperature in an atmospheric DBD reactor to assess the effect of precursor carbon double bond unsaturations. The specific plasma deposition rate (k0) as a function of the Yasuda factor (Yf) is quantified empirically by: k0 = b (1 - exp(-a Yf/b)). Fourier transform infrared analysis indicates a loss of carbonyl functionalities with increasing plasma power, and Raman microscopy shows C£C double bonds in all plasma films. The methacrylate-like plasma films are found to be heterogeneous with a volatile and a cross-linked fraction observed by thermogravimetric analysis. Differential scanning calorimetry reveals a low glass transition temperature and a characteristic residual reactivity of the coatings. The effect of precursor carbon double bond unsaturations on the specific plasma deposition rate (k0) and thermal properties of plasma deposited methacrylate-like films is assessed in this work. A significant increase in the plasma deposition rate with increasing number of precursor C£C bonds is found. In general, two distinctive thermal characteristics are observed by DSC: a relatively low Tg and a residual reactivity in the first heating of the DSC experiment.

Surface corrosion product formation is one of the important factors affecting the corrosion rate and hydrogen uptake in a H2S environment. However, it is still unclear how the base material composition will affect the corrosion products that are generated, and consequently their impact on the corrosion rate. In this paper, corrosion product formation and the impact of the Mo content of the base material on the composition of the corrosion products and hydrogen absorption in a sour environment was investigated. The corrosion layer was composed of a double layered mackinawite (FeS1−x) structure, which was enriched with molybdenum and chromium. The layers were formed via two different mechanisms, i.e., the inner layer was created via a general oxide film formation corrosion mechanism, whereas the upper layer was formed by a precipitation mechanism. The presence of this double corrosion layer had a large influence on the amount of diffusible hydrogen in the materials. This amount decreased as a function of contact time with the H2S saturated solution, while the corrosion rate of the materials shows no significant reduction. Therefore, the corrosion products are assumed to act as a physical barrier against hydrogen uptake. Mo addition caused a decrease in the maximal amount of diffusible hydrogen.

This work studies the influence of the proportional change in discharge power and the monomer feed on the morphology and the chemistry of atmospheric plasma deposited films. Atmospheric plasma coatings of allyl methacrylate were deposited using dielectric barrier discharge plasma under different conditions but always under the same ratio between the discharge power and monomer feed (W/FM). It is shown that a constant W/FM does not necessarily provide the same chemistry and the same morphology for atmospheric pressure plasma. This is explained by the higher discharge power of the plasma resulting in an increase of streamers which alter the distribution of energy among the plasma species. On the surface of the deposited coatings, globular-like features were observed, which are suggested to be formed in the volume of the discharge. The deposition rate is also influenced. providing thicker coatings, when high monomer feed/high power are used. Finally, infrared spectra showed a higher retention of the ester functionality at high power/high monomer feed.

The galvanostatic anodizing behavior of additive manufactured (AM) Al-Si10-Mg alloy was studied in H 2SO 4 electrolyte. The analysis of the voltage vs time response was complemented with a systematic characterization of the anodic oxide layer using a variety of techniques. In addition, a cast alloy of approximately the same chemical composition as that of theAMspecimens was used as a reference in this study. Significant differences were found in the voltage-time characteristics of the samples analyzed. Besides, an anisotropic anodizing behavior was observed in the additive manufactured specimens. Due to the fine silicon microstructure present in the additive manufactured samples, the anodic oxide growth was much more obstructed than for the cast alloy. Nevertheless, even though the oxide layer was generally thinner in the AM samples for the same conditions and anodizing time, a much more continuous and uniform oxide layer was found in the additive manufactured specimens compared tothe cast alloy. The porous structure was found to be greatly affected by the fine distribution of the silicon phase in the AM parts.

Additive manufacturing (AM) of metals offers new possibilities for the production of complex structures. Up to now, investigations on the mechanical response of AM metallic parts show a significant spread and unexpected failures cannot be excluded. In this work, we focus on the detection of fatigue cracks through the integration of a Structural Health Monitoring (SHM) system in Ti-6Al-4V specimens. The working principle of the presented system is based on the integration of small capillaries that are capable of detecting fatigue cracks. Four-point bending fatigue tests have been performed on Ti-6Al-4V specimens with integrated capillaries and compared to the reference specimens without capillaries. Specimens were produced by conventional subtractive manufacturing of wrought material and AM, using the laser based Directed Energy Deposition (DED) process. In this study, we investigated the effect of the presence of the capillary on the fatigue strength and fatigue initiation location. Finite element (FEM) simulations were performed to validate the experimental test results. The presence of a drilled capillary in the specimens did not alter the fatigue initiation location. However, the laser based DED production process introduced roughness on the capillary surface that altered the fatigue initiation location to the capillary surface. The fatigue performance was greatly reduced when considering a printed capillary. It is concluded that the surface quality of the integrated capillary is of primary importance in order not to influence the structural integrity of the component to be monitored.

This work presents first results of the study on the influence of the LBE oxygen concentration on the initiation of dissolution corrosion in 316L austenitic stainless steels. 316L steel specimens were exposed at 450 °C to static liquid LBE with controlled and constant oxygen concentration of 10−5, 10−6 and 10−7 mass% for 1000 hours. Corroded specimens were analysed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Limited oxidation corrosion and no dissolution corrosion was observed in the specimens exposed to LBE containing 10−5 and 10−6 mass% oxygen, while dissolution corrosion with a maximum depth of 59 μm was found in the specimen exposed to LBE containing 10−7 mass% oxygen.

Methyl methacrylate (MMA) is deposited on aluminum substrates using atmospheric dielectric barrier discharge plasma. The thermal properties of plasma deposited MMA (pdMMA) films of 0.5 to 1 μm thickness are evaluated as a function of plasma power and precursor mass feed. Thermogravimetric analysis indicates a low molecular weight fraction in all pdMMA films, which lowers their thermal stability. Differential scanning calorimetry (DSC) is used to quantify the glass transition (Tg) and residual reactivity of the pdMMA thin films. For all plasma conditions, the Tg remains inferior to conventional PMMA, and ranges from 20 °C in the monomer-deficient domain to 56 °C in the energy-deficient domain. A residual reactivity is measured in the first DSC heating of all pdMMA films, showing an exothermicity up to -160 J g-1. A systematic thermal analysis of thin organic plasma films in relation to the plasma conditions remains scarce in literature. In this work, the focus is on the quantiication of thermal properties of pdMMA ilms produced using a DBD reactor operating at atmospheric pressure. The glass transition and residual reactivity of the plasma ilms are measured by DSC as a function of precursor mass iow and input plasma power.

By positioning the layer containing Ce ( dbp ) 3 close to the coating–metal interface, the effective use of the inhibitor is promoted, as the leaching out towards the metal surface is facilitated. The chemical nature of Ce ( dbp ) 3 did not undergo any significant change due to the plasma discharge. The coatings with Ce ( dbp ) 3 were compared with equivalent coatings without incorporated corrosion inhibitor and it was shown that Ce ( dbp ) 3 improved the corrosion performance when the coating was mechanically damaged. Optical evaluation of the coatings showed a significant decrease in the corrosion, especially in the area under the coating. However, the low corrosion resistance values obtained by electrochemical impedance spectroscopy indicate that corrosion was not inhibited all over the scribed area.

In situ electrochemical scanning tunneling microscopy (ECSTM) was applied to analyze the local susceptibility to corrosion at different grains of cryogenically rolled microcrystalline copper in a HCl solution, and combined with electron backscatter diffraction (EBSD) and field emission scanning electron miscroscopy (FE-SEM) to discuss the relationship between nanometer scale corrosion resistance and crystallographic orientation. The results show that the thickness of the air-formed oxide layer is grain-dependent with the largest values exceeding locally by a factor of 2 the macroscopic value (2.8 nm) measured electrochemically. Anodic dissolution is also grain-dependent with dissolving grains observed to neighbor corrosion-resistant grains. A nearly random texture prevented an EBSD-based assignment of the crystallographic orientation of the grains observed by ECSTM. However, comparison of the etched surface morphology measured in situ by ECSTM and ex situ by FE-SEM suggested that the faster dissolving grains were oriented closer to 111 //ND or in between 111 //ND and 110 //ND while the neighboring corrosion-resistant grains were oriented closer to 001 //ND. The higher step density measured by ECSTM on the grains corroding faster despite possibly 111 //ND oriented terraces confirms the role of surface defects related to misorientation on the corrosion susceptibility.