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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.

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.

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.

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 (

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.

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...

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.

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.

Corrosion of reinforcement steel forms a huge problem worldwide. A possible remedy for this problem is the application of corrosion inhibitors. The purpose of this research is to evaluate different inhibitors for both types of corrosion that can occur in reinforced concrete: pitting corrosion (by chloride attack), and uniform corrosion (by a drop in pH). Potentiodynamic polarization measurements in realistic concrete pore solutions (CPS) revealed three critical situations — representing pitting and uniform corrosion, and the combination — in which the inhibitor needs to act. According to polarization experiments and micrographs Na 2 MoO 4 is the best performing inhibitor for the three cases. Our XPS measurements are in line with the proposed inhibitor mechanism by Vukasovich (1986), which is very complex and depends on whether the surface is active or passive to start with. In conclusion Na 2 MoO 4 is a possible — and environmental-friendly — candidate to prevent corrosion of reinforcement steel.

Microbial healing of concrete cracks is a relatively slow process, and meanwhile the steel rebar is exposed to corrosive substances. Nitrate reducing bacteria can inhibit corrosion and provide crack healing, by simultaneously producing NO 2 − and inducing CaCO 3 precipitation. In this study, the functionality of one non-axenic and two axenic NO 3 − reducing cultures for the development of corrosion resistant self-healing concrete was investigated. Both axenic cultures survived in mortar when incorporated in protective carriers and became active 3 days after the pH dropped below 10. The non-axenic culture named “activated compact denitrifying core” (ACDC) revealed comparable resuscitation performance without any additional protection. Moreover, ACDC induced passivation of the steel in corrosive electrolyte solution (0.05 M NaCl) by producing 57 mM NO 2 − in 1 week. The axenic cultures produced NO 2 − up to 26.8 mM, and passivation breakdown and pitting corrosion were observed. Overall, ACDC appears suitable for corrosion resistant microbial self-healing concrete.