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This paper describes the combined detection of coating and rust damages on painted metal structures through the multiclass image segmentation technique. Our prior works were focused solely on the localization of rust damages and rust segmentation under different ambient conditions (different lighting conditions, presence of shadows, low background/object color contrast). This paper method proposes three types of damages: coating crack, coating flaking, and rust damage. Background, paint flaking, and rust damage are objects that can be separated in RGB color-space alone. For their preliminary classification SVM is used. As for paint cracks, color features are insufficient for separating it from other defect types as they overlap with the other three classes in RGB color space. For preliminary paint crack segmentation we use the valley detection approach, which analyses the shape of defects. A multiclass level-set approach with a developed penalty term is used as a framework for the advanced final damage segmentation stage. Model training and accuracy assessment are fulfilled on the created dataset, which contains input images of corresponding defects with respective ground truth data provided by the expert. A quantitative analysis of the accuracy of the proposed approach is provided. The efficiency of the approach is demonstrated on authentic images of coated surfaces.

Based on the principle of a micropore-filling electrolyte, a graphene composite conductive coating combined with impressed current cathodic protection (ICCP) technology was constructed and applied in a marine atmospheric environment. To further explore the optimal protection parameters of the graphene composite conductive coating combined with ICCP technology in a marine atmospheric environment, the effects of the coating damage area (A), impressed voltage (B), and distance from the contact point (C) on the protective performance of the coating were investigated via orthogonal experiments. The optimal protection voltage and effective protection distance were verified by super-depth-of-field morphology observations and electrochemical tests. The orthogonal experimental results show that the primary and secondary orders affecting the protective performance of the conductive graphene composite coating are as follows: applied voltage (B) > coating damage area (A) > distance from the point of contact (C). The optimal protective parameters of the coating in the marine atmospheric environment are an applied voltage of 0.7 V, a damage rate of ≤1%, and a distance from the point of contact of 190 mm. The experimental results show that the corrosion potential of the sample is the highest under an applied voltage of 0.7 V, and the corrosion products do not diffuse to the surface of the coating. When the polarization resistance (Rp) values at 110 mm and 190 mm from the negative electrode at the point of contact are greater, the corrosion rate is lower, and the coating protection performance is better.

A widely used coating system for corrosion mitigation of offshore steel structures is thermally sprayed aluminium (TSA). Even though these coatings have been used for decades, it is not always clear how they perform in service over long periods, particularly if damaged during installation or in service. To understand the corrosion behaviour of damaged TSA coatings in seawater and their tolerance to levels of damage, TSA coatings (1050 Al) were prepared on carbon steel substrates using wire arc spray and tested in synthetic seawater. Prior to testing, various levels of holidays or damage (~5%, 10%, 15% and 18%) reaching the steel substrate were drilled on the front surface of the coated specimens. Open circuit potential was measured and linear polarization resistance technique was used to calculate the corrosion rate. The work showed that the TSA coatings polarised steel to potentials below −800 mV (Ag/AgCl) at 25 °C, even in the presence of damage or holiday (up to ~18%). The SEM/EDX and XRD data confirmed the presence of brucite and aragonite in the damage region. The presence of damage impacted the short-term corrosion rate at the start, but did not significantly affect the overall corrosion performance of the TSA coatings in 420 days of testing.

The influence of a direct current (DC) stray current on the corrosion and cathodic disbondment of X80 steel coated with a polyethylene (3PE) coating in 3.5% NaCl solution was studied by immersion experiments, electrochemical tests, three-dimensional microscopy, and a surface analysis. The results showed that the potential of the X80 steel sample shifts under the direct current. After 100A/m2 DC interference was applied, the potential of the sample in the anode region positively shifted from –0.68 to –0.43 V. At the same time, the sample in the cathode region negatively shifted to –1.45 V. Under the DC anode action, the X80 steel corrosion exhibited no passivation and followed Faraday’s law of electrolysis, in which the corrosion rate is proportional to the current density. Three-dimensional (3D) digital microscopy showed that, as the DC current increased, the depth of the corrosion pit also increased (gradually), indicating a higher corrosion degree. The sample in the cathode region only underwent a hydrogen evolution reaction, which caused cathodic disbondment of the coating. The stray current had a critical current density for the coating disbonding: the coating delamination area reached its maximum and then remained unchanged.

Low Infrared emissivity coating (LIREC) is prone to generating some problems such as bulges, degumming, and abrasion. In order to study whether the performance of LIREC under different damages can meet the work needs, it is essential to timely measure and evaluate the performance state of LIREC in the application process. The existing methods for measuring the damage of LIREC have some disadvantages such as expensive equipment, complex operation, and inaccurate measurement results. In this paper, a measurement method of LIREC damage capability based on thermal imager is proposed. The radiation temperature is measured by thermal imager, the real temperature and ambient temperature of coating surface are measured by thermocouple, and the emittance of coating surface is calculated. Non-contact and continuous large-area emissivity measurements are carried out on the damaged parts of the coating and verified by experiments. The measurement results show that the different damage types and damage degrees directly affect the measurement results of LIREC. Wear damage increases the emissivity of the coating while debonding damage basically does not change the coating emissivity. Shedding damage of small diameter forms voids, which causes the increase of the damage parts of emittance. In addition, bulge damage impedes temperature transfer and reduces emissivity. This method can timely and accurately measure and evaluate the performance state of LIREC and can provide a new idea for the accurate measurement of damage emissivity of LIREC.

Standing wave field distributions in three classic types of graded-index antireflection coatings are studied. These graded-index antireflection coatings are designed at wavelengths from 200 nm to 1200 nm, which is the working wavelength range of high energy laser system for inertial-fusion research. The standing wave field distributions in these coatings are obtained by the numerical calculation of electromagnetic wave equation. We find that standing wave field distributions in these three graded-index anti-reflection coatings are quite different. For the coating with linear index distribution, intensity of standing wave field decreases periodically from surface to substrate with narrow oscillation range and the period is proportional to the incident wavelength. For the coating with exponential index distribution, intensity of standing wave field decreases periodically from surface to substrate with large oscillation range and the period is also proportional to the incident wavelength. Finally, for the coating with polynomial index, intensity of standing wave field is quickly falling down from surface to substrate without an obvious oscillation. We find that the intensity of standing wave field in the interface between coating and substrate for linear index, exponential index and polynomial index are about 0.7, 0.9 and 0.7, respectively. Our results indicate that the distributions of standing wave field in linear index coating and polynomial index coating are better than that in exponential index coating for the application in high energy laser system. Moreover, we find that the transmittance of linear index coating and polynomial index coating are also better than exponential index coating at the designed wavelength range. Present simulation results are useful for the design and application of graded-index antireflection coating in high energy laser system.

Ta 2 O 5 /SiO 2 bi-layer anti-reflection (AR) films have been deposited for various wavelengths on ultra-smooth, large fused silica (FS) substrates using the sol-gel dip-coating technique. This method facilitates the development of transmission windows with high laser-induced damage thresholds (LIDT). Super-polished, 50 mm diameter flat FS substrates were AR-coated on both sides using this simple and cost-effective approach. The nearly stoichiometric thin films of Ta 2 O 5 and SiO 2 were synthesized using halide-free precursors—tantalum ethoxide and tetraethyl orthosilicate, respectively. The morphology, composition, and optical properties of these thin films were characterized before applying them as bi-layer AR coatings on FS substrates. The refractive indices of the Ta 2 O 5 and SiO 2 thin films were determined to be 1.75 and 1.44, at 1000 nm, respectively. AR coatings were deposited for four target wavelengths—850 nm, 1053 nm, 1300 nm, and 1550 nm—by varying the film thickness with precise control over the withdrawal speed during the dip-coating process. Deposition parameters were optimized to minimize optical absorption, achieving a maximum transmission of >99% and reflectivity of <1% for all AR coatings. All sol-gel AR-coated FS transmission windows demonstrated a high LIDT of ~20 J/cm 2 , making them highly suitable for high-energy laser applications. Graphical Abstract Highlights Anti-reflection coatings on super-smooth large FS substrates using sol-gel dip coating. Development of >99% transmission windows using Ta 2 O 5 /SiO 2 bi-layer. Laser induced damage threshold (LIDT) of >20 J/cm 2 is achieved. AR coatings at wavelengths 850, 1053, 1300, and 1550 nm have been developed. RMS roughness of 2 Å and λ/6 surface flatness are obtained for the AR coatings.

Thermal spray processes have been developing toward lower particle temperature and higher velocity. Latest generation high-velocity oxygen-fuel (HVOF) and high-velocity air-fuel (HVAF) can produce very dense coating structures due to the higher kinetic energy typical for these thermal spray processes. Thermally sprayed coatings usually contain residual stresses, which are formed by a superposition of thermal mismatch, quenching and, in case of high kinetic energy technologies, peening stresses. These stresses may have a significant role on the mechanical response and fatigue behavior of the coating. Understanding these effects is mandatory for damage tolerant coating design and wear performance. For instance, wear-resistant WC-CoCr coatings having high compressive stresses show improved cavitation erosion performance. In this study, comparison of residual stresses in coatings sprayed by various thermal spray systems HVOF (Thermico CJS and Oerlikon Metco DJ Hybrid) and HVAF (Kermetico AcuKote) was made. Residual stresses were determined through thickness by utilizing Tsui and Clyne analytical model. The real temperature and deposition stress data were collected in the coating process by in situ technique. That data were used for the model to represent realistic residual stress state of the coating. The cavitation erosion and abrasion wear resistance of the coatings were tested, and relationships between residual stresses and wear resistance were discussed.

Xray free‐electron lasers (XFELs) enable experiments that would have been impractical or impossible at conventional X‐ray laser facilities. Indeed, more XFEL facilities are being built and planned, with their aim to deliver larger pulse energies and higher peak brilliance. While seeking to increase the pulse power, it is quintessential to consider the maximum pulse fluence that a grazing‐incidence FEL mirror can withstand. To address this issue, several studies were conducted on grazing‐incidence damage by soft X‐ray FEL pulses at the European XFEL facility. Boron carbide (B4C) coatings on polished silicon substrate were investigated using 1 keV photon energy, similar to the X‐ray mirrors currently installed at the soft X‐ray beamlines (SASE3). The purpose of this study is to compare the damage threshold of B4C and Si to determine the advantages, tolerance and limits of using B4C coatings. The damage threshold fluences of silicon (Si) and boron carbide (B4C)‐coated Si at 1 keV and 9 mrad grazing incident angle are compared. Results show that B4C has a damage threshold approximately twice that of Si, highlighting the advantages of using B4C coatings for enhanced durability.

Corrosion of metal structures and consumer products has been a significant problem since the start of the industrial revolution. However, the inhibition and prevention of corrosion have only been an active area of study in the last century. The need for smart and functional coatings has recently become a large area of interest due to the ability of these coatings to be adapted to a variety of materials, mechanical and chemical conditions, and sporadic environmental conditions. One of the most viable methods by which corrosion can be prevented is through coatings. Self-healing coatings demonstrate a novel method of autonomic repair for microcracks using self-healing polymers encapsulated with polymerizable species into microparticles and nanoparticles. Additionally, these microparticles and nanoparticles can also be loaded with corrosion inhibitors that are released upon mechanical or chemical damage, thereby reducing corrosion. The use of superhydrophobic coatings leads to improved corrosion resistance due to the modification of the wettability of the coating, thereby changing its hydrophilic or hydrophobic response. This review details and provides a new perspective on self-healing and superhydrophobic coatings as well as future outlooks.