The properties of the coating depend, among other things, on the preparation of the substrate surface and the spray parameters. One of the key properties of the coating is its adhesion to the substrate. Suitable preparation of the substrate surface has a great influence on the adhesion of the thermal spray coating. This work aims to study the influence of surface preparation on roughness of substrate and the resulting surface adhesion of coating. Another aim was to compare the effect of the chosen adhesion measurement method. A series of measurements of the roughness of the samples after grit blasting was performed. The effect of using new and used corundum was also taken into account. The selected coating for testing was TWAS (twin Wire Arc Spray) sprayed Zn15Al. The substrate material was low carbon steel 1.0570. The following adhesion measurement methods were chosen for the experiment - adhesion tensile test according to ASTM C633 - 79 standard, method using a special sample holder based on the ASTM C633 - 79 standard. In addition, a series of measurements were performed using Elcometer 510 Model T.

Metal structures in offshore facilities are usually protected from corrosion using Zn-Al coatings even though they are subjected to collective stress conditions. This paper evaluates a post-treatment called machine hammer peening and its effect on surface finish, induced residual stresses, and near-surface microstructure of thermally sprayed ZnAl4 coatings. As expected, coating roughness was reduced from about Rz = 53.5 μm in the as-sprayed condition to 10.4 μm after treatment and coating densification was revealed in the near-surface zone. Residual stresses, which were surprisingly compressive in the as-sprayed condition, were likewise affected by the peening process, reaching a maximum of 200 MPa. The influence of peening direction and other such parameters were also investigated as part of the study.

The aim of this study is to characterize the mechanical behavior of wire-arc sprayed Zn-Al coatings and correlate the results with microstructure via computational techniques. High-resolution microstructural images obtained by SEM were imported into NIST-developed FEA software, which calculates macroscale properties based on user-selected features such as voids, pores, cracks, and splat boundaries. To assess the validity of the approach, elastic modulus was measured various ways and the results compared to the simulated value. Resonant frequency analysis provided the most accurate measurement, which was found to be closest to the simulated value.

In recent studies, crack formation was observed in oxidized areas of wire-arc sprayed Zn-Al coatings. As corrosion tests show, these cracks allow electrolyte to penetrate the coating, reducing effective service lifetime. Wire-arc sprayed coatings usually exhibit tensile residual stresses with the potential to cause such cracking. To determine the extent of that potential, the stress state of Zn-Al coatings was measured and correlated with corrosion test results. Residual stress was obtained using the sin2ψ method based on XRD analysis and the results are combined with those of previous studies, forming a hypothesis for the root cause of crack formation in wire-arc sprayed Zn-Al coatings, its effects, and its control.

The economic use of offshore wind turbines requires a reliable and long-lasting corrosion protection. Sophisticated multilayer coating systems consisting of a thermal spray coating – mainly ZnAl15, a sealer and several layers of organic coating – have been proven to provide such protection. Damages to these duplex-coatings can, however, not be prevented necessitating on-site repair. In case of severe damages, the remaining coating close to the damage is often removed and subsequently, the duplex coating is rebuilt from scratch. In the present study, two integrated coating removal and substrate pre-treatment methods are investigated. For this purpose, duplex-systems were produced, artificially damaged by milling and afterwards treated by either grit blasting or with a rotating steel-wire brush, i.e. a Monti Bristle Blaster. Afterwards, the duplex coating was re-applied in the considered area. To evaluate the influence of the pre-treatment method on the coatings’ corrosion protection potential, a 38 week-long salt spray test was used. The test revealed a pronounced influence of the pre-treatment method on the corrosion protection potential. In case of grit blasting, no substrate corrosion could be detected. The use of a Bristle Blaster, however, resulted in coating failure and some spots of red rust.

For many decades thermally sprayed corrosion protection systems on the basis of ZnAl or Al carry out their service for structures in coastal areas, the offshore sector, as CUI (Corrosion Protection under insulation) or anywhere where the properties of thermally sprayed corrosion protection systems bring important advantages in terms of durability. A thermally sprayed corrosion protection system is about to protect the structure 25 to 30 years against corrosion. During this time it may be damaged due to factors like construction work, improper handling or simple aging. There are many standards and regulations, which describe the initial design of thermal spray systems, however they remain silent regarding repair. In particular, a mending of partial regions is hardly described. Specific repair instructions are rare and if present, they differ from one another. Overall there is a lack of knowledge of the proper procedures for partially repairing thermal spraying systems. This project was concerned with tangible corrosion-technical issues of the coating repairs: How does the critical overlap area perform? Have organic coatings benefits? To what extent does a renewed damage affect the lifetime? The aim of the study was to develop practice-relevant instructions for the repair of thermally sprayed duplex systems.

Additive manufacturing (AM) techniques give access to completely new manufacturing processes. AM techniques using metals, ceramics, or plastics feedstock are predestined for lightweight construction and for components with complex shapes or internal functions. AM processing with plastics stands out due to the low density of polymers, a good process capability, and low initial costs. The properties of polymer components are extremely dependent on the utilized plastics and the reinforcements, e.g. in the form of fibres. Furthermore, coatings can improve the properties and enhance the possible range of applications for plastics. In the present study, PLA (polylactic acid) was printed utilizing Fused Layer Modeling (FLM). The surfaces of the PLA samples were directly structured with pits with different widths during printing. Subsequently, the surfaces were coated with ZnAl 2 by means of Twin Wire Arc Spraying (TWAS). Adhesion tests meeting DIN EN 582 were conducted to measure the adhesion of the coating on the structured plastic surface. The results were compared to the adhesion of ZnAl 2 coatings on grit blasted and as-built surfaces. Overall, the surface adhesion was significantly better for the samples with directly structured surfaces. Hence, a direct structuring of the surface during a 3D building process promises to be an outstanding possibility to prepare surfaces prior to coating processes.

In this investigation, different atomizing gases, arc wire spray guns, and wire sizes were used to deposit ZnAl coatings on high-strength steel substrates. Sample sets corresponding to different gas mixtures and pressures as well as other parameters were produced and the coatings obtained were evaluated based on morphology, porosity, composition, phase distribution, and oxide content. The results are presented and discussed, particularly with regard to corrosion lifetime and performance.

To obtain the desired functionality and provide sustainability for steel structures, costly maintain and repair is needed. For use in particularly critical environments thermally sprayed coatings based on zinc/ aluminum in combination with a sealing supply many advantages. The subject of the ongoing research project is to deepen the knowledge about the influence of the thermal spray process, the spraying parameters, the manufacturing and especially the sealing process on the durability of sealed ZnAl-corrosion protective coatings. Verification is provided by state of the art testing methods to evaluate the coatings quality. The overall objective of the study is to provide recommendations on approaches and boundary conditions for manufacturing and sealing of thermally sprayed coatings for corrosion protection.

This paper presents key findings from an ongoing study on the marine corrosion behavior of thermally sprayed zinc and aluminum coatings. Zn, Al, and Zn-Al layers of varied thickness were applied to twelve steel pipes by arc and flame spraying and subjected to different post-spray treatments such as sealing and painting. The pipes are mounted vertically on a test rig in the Pacific Ocean and have been inspected annually to record the appearance and thickness of the coatings. After 7 years, the Zn coatings began to show signs of degradation in the immersed portion of the pipe, although no such changes occurred with Al and Zn-Al coatings. After 18 years, heavily damaged sections of three pipes were removed and new pipe was welded in place. The repaired regions were coated with Al-5%Mg, which has performed well so far.

The aim of this study is to compare the quality of corrosion-resistant thermal spray coatings depending on where and how they are applied. ZnAl 15 coatings were applied to S235 steel substrates by wire arc spraying in keeping with standard (EN ISO 2063) practice. The coatings were sprayed under factory conditions and in a simulated onsite environment using manual and automated methods. As-sprayed and sprayed-and-sealed coating samples were subjected to climate-cycle and corrosion testing. Coatings applied onsite varied in quality to a much greater extent than those sprayed under workshop conditions. Poor quality, and implicitly a lower corrosion resistance, was widely detected in coatings where ZnAl was manually sprayed under simulated onsite conditions. The implications of the study are particularly relevant to the sustainability of coastal and offshore wind power generators due to maintenance challenges.

In this work, wire arc spraying is used to produce coatings in which oil-filled capsules are incorporated in the metal matrix. The coatings were deposited on carbon steel substrates using commercially available Zn-Al and FeNiCr alloy wires. The capsules were injected almost radially toward the substrate using an independent slurry feeder. No signs of degradation were observed during spraying and the coatings were able to keep a low coefficient of friction. Wear tracks produced by the steel ball used for friction testing were examined and volume loss was determined based on wear track profiles.

This work assesses various ways of improving the corrosion protection and service life of thermally sprayed coatings used in offshore structures. Test results show that improvement is possible even in the case of Zn-Al15 spray coatings and, that in some cases, coating thickness can be reduced without loss of corrosion protection. Test samples were prepared by arc and cold-gas spraying and some of the coatings were sealed. The protective characteristics of the various coating systems were evaluated in a 25-week cyclic aging test as defined in ISO 20340. The results are compared based on the degree of blistering, rusting, and corrosion penetration at the scratch as well as adhesion to the substrate.

Thermally sprayed coatings of zinc, and in particular zinc-aluminium alloys, offer maximum corrosion protection for steel structures and reinforcing steel in concrete. They are primarily produced by arc or flame spraying. The surfaces of zinc and zinc alloy spray coatings can be protected by sealing top coats. This produces an optimum combination of passive and active corrosion protection and allows a service life of over 20 years. The development of new materials assumes intensive investigations. This paper provides an overview of the properties of thermally sprayed zinc and zinc-aluminium alloys as well as their microstructure and investigates the corrosion protection effect in tests and near-practical conditions.

The effect of the hardness in the substrate surface blasted by a grit blasting process on the adhesive strength of Zn-Al sprayed coatings is investigated to find the adhesive strength is improved by work hardening of the substrate surface. The adhesive strength between a substrate of a carbon steel and sprayed coatings of Zn-Al alloy sprayed by a wire flame spraying process is measured. The substrate is roughened by the grit blasting process with white alumina girt in various blasting angles and blasting time. The hardness is measured in around 20 micro-meter depth from the substrate surface. The adhesive strength increases with increasing the hardness even if the surface roughness is almost same. There is the definite correlation between the adhesive strength and the hardness rather than the surface roughness.

Zn, Zn-Al and Zn-Mg coatings have been produced by cold spraying. By careful tuning alloy compositions and spray conditions, dense coatings are produced with a hardness of 200 HV0.01 that are up to four times harder than pure bulk Zn, thus meeting the requirements for print applications. These new developments open opportunities for producing harder and more wear resistant coatings, which may allow for the production of larger number of copies without compromising quality.

Thermal spray of Zn, Zn/Al, or Al is extensively used to make anticorrosion coatings on steel structures. Twin arc spray and wire flame spray are the two most practised processes to achieve such coatings. This paper presents measurements of particle emissions generated by these two processes. Sampling and analysis of aerosols generated by both processes have been carried out inside the exhaust ductwork using various instruments: an ELPI impactor, a CNC (Condensation Nucleus Counter), a TEOM microbalance and sampling filters allowing sampling for SEM observations. Electric arc spraying produced much more fumes of ultra fine particles than flame spraying. Aluminum spraying also produces large fume quantities compared to the Zn spraying under the same conditions. The aerosol comprised submicron particles and 95% of the numerical particle size distribution was less than 100 nm. The nanometric nature of the fume particles was confirmed by observations on the SEM. The strong dilution caused by compressed air has the effect of strongly limiting particle coagulation and, in turn, the size of the agglomerated particles. Electric arc spray has taken market share versus wire flame spray for Zn, ZnAl, or Al spraying, but this study shows that it generates much more particle emissions.

Ductile iron pipes (DIP) have been used worldwide since 1960s for water transmission and distribution mains. By 1979, ductile iron pipe largely replaced cast iron as the predominant material in water industry. Zn and Zn/Al 85/15 coatings applied by thermal spray technique are used for the protection of the ductile iron pipe against corrosion in heterogeneous soil conditions. In this study, heat treated and non-heat treated ductile iron pipe samples were coated with Zn and Zn/Al 85/15 in optimum spray parameters by twin wire electric arc (TWEA) spraying technique. The coatings were investigated by optical microscopy, scanning electron microscopy (SEM), and analyzed by energy dispersive spectrometer (EDS). Both Zn and Zn/Al 85/15 coatings showed fairly good lamellar structure with acceptable amount of internal porosities and oxides. Annealing oxides available on pipe surface helped the bonding of coatings. The protection performance of the coatings was compared with accelerated corrosion (salt spray) test according to the ASTM B 117 and corrosion products were analyzed by SEM and EDS technique. Salt spray test results showed that Zn/Al 85/15 coatings have better corrosion resistance than Zn coatings and annealing oxide on ductile iron pipe acts as a good corrosion resistant protective layer.

Traditional metal spraying techniques, which have been used in industry for decades, such as Wire Flame and Twin-Wire Arc are classified as low velocity processes because the sprayed material is conveyed by compressed air having subsonic velocity. In order to improve the bond strength, HVAF was applied for thermal spraying for anticorrosion protection. In this paper, zinc-aluminium (Zn-Al) coatings thermal sprayed using the HVAF method are analysed. The thermal sprayed coatings were characterized by the standard techniques, such as light microscopy, scanning electron microscopy with energy-dispersive spectroscopy, X-ray diffraction, salt spray and bond strength tests. The results show that thermal sprayed coatings have a dense structure, a high bonding strength, low presence of oxides and high resistance to corrosion. This is attributed to high flow/particle velocities and relatively low combustion temperatures of HVAF in comparison with other thermal spraying technologies. High spray rate and good coating quality make the HVAF thermal spray method a viable alternative to the conventional Wire Flame and Twin-Wire Arc methods for thermal spraying of Zn-Al coatings.

Twin wire arc sprayed Zn, Al and Zn/Al 85/15 coatings were investigated for comparison of their corrosion resistance, electrochemical behavior. The Zn, Al and Zn/Al 85/15 coatings possess prominent electrochemical passivation behavior. Oxide formation mainly onto the coating surfaces were identified with energy-dispersive X-ray analysis and were believed to be responsible for the passivation phenomena observed in the electrochemical polarization. Zn and Al are more negative in electrochemical potential than iron. Zn coatings act as a sacrificial anode and providing cathodic protection. Aluminum shows passive corrosion protection according to stable oxide layer occurs on coating surface. Zn/Al 85/15 coating show two corrosion protection mechanisms together. In this study, steel samples were coated with Zn, Al and Zn/Al 85/15 in optimum conditions by wire arc spraying technique. These coatings were investigated behaviors of polarization and corrosion resistance with electrochemical test.