The primary goal of this research work is to enable methane decomposition in absence of inert conditions as well as comparatively lower catalyst activation temperatures using thermally sprayed optimized catalytic coatings. Preliminary tests of twin-wire arc thermally sprayed coatings of metal alloys confirm the decomposition of methane gas.

The applications of Wire Arc Spraying (WAS) include large-area corrosion protection coatings e.g. the protection of off-shore wind power plants. While WAS is cost efficient and well-known, the inherent instabilities can lead to coating defects and subsequent vulnerabilities in the corrosion protection coating. The occurrence of these process-related fluctuations cannot be predicted by deterministic models. However, these fluctuations can be monitored in situ, analyzed and finally minimized. A sensor unit is set up on the free jet of a WAS process using ZnAl15 wire. Voltage, amperage, noise and wire feed rate are measured in situ at a sampling rate of 80 MHz. Following a design of experiments approach, 64 different parameter settings are run and measured. For that purpose, voltage, atomizing gas and wire feed rate of the free gas jet have been varied. A generalized linear model (GLM) is trained on the dataset. A Fast Fourier Transformation (FFT) in conjunction with smoothing filters is conducted. Adopting the GLM enabled the calculation of parameters that minimize process fluctuations. Plots in the form of response surfaces depict the influence of the varied parameters on the process stability. A signal analysis using FFT revealed major periodic changes of the voltage in the range of 0.5-1 kHz next to process control-related frequencies at 20 kHz. The mounting and structuring of the data as well as the calculation of key figures is fully automated. Due to the high degree of automation, large quantities of data can be processed. In the future, a simplified version of the adopted sensor unit may be adopted to optimize parameters in an autonomous way. This can ensure not only the minimization of process fluctuations for any chosen feed wire, but also indicate irregularities in the process. The high-resolution recording and automated analysis of the data allows the determination of optimized parameters as well as major underlying frequencies.

Thermal spraying, especially wire arc spraying, represents a strong growing and developing technology due to the possibility of current modulation. However, achieving consistently high coating quality in an automated production environment is strongly influenced by a large number of sensitive process parameters, including base current, pulse current, pulse duration, impulse frequency, alternating current frequency, and wire speed. To monitor and store the coating process data, a holistic process monitoring system was designed and tested numerous times. The scalable system is able to compare a wide variety of different process signals on one timeline. In addition to arc spraying, it can also be used for other arc processes. Custom software enables the comparison and analysis of selected process data sets in order to identify and correct irregularities in the process and the resulting coating. This article uses selected examples to demonstrate the opportunities and limitations of the system.

Sensors to measure gas velocities in high temperature flows need to be robust, low-profile so that they do not obstruct the flow, and easy to apply on metal surfaces. Thermal spray offers a method of making low-cost sensors that can be applied on large areas. Plasma spray was used to deposit an electrically insulating layer of alumina on a 316 stainless steel block. A 17 mm diameter heater coil was deposited on top of the alumina layer by spraying Nichrome from a twin wire arc spray system through a 3D printed polymer mask. A thermocouple junction was built next to the heater by inserting an insulated Constantan wire through a vertical hole drilled in the steel block and spraying steel on the top of the hole to close it and form an electrical connection between the wire and the surrounding substrate. The junction of the wire and the steel formed a thermocouple whose output voltage was calibrated. A flow loop was built to calibrate the sensor by passing air over it at velocities of up to 5 m/s. A series of 2 min long voltage pulses were applied to the heater, increasing its temperature by approximately 5°-10°C each time, before letting it cool. A calibration curve was developed of the air velocity as a function of the time constant for cooling of the sensor.

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.

Plasma Transferred Wire Arc (PTWA) is a well-established thermal spray process that is used in high-volume production by multiple automotive OEMs. Benefits of these PTWA thermal spray coatings include closer bore spacing, improved thermal transfer, lower bore distortion, increased resistance to corrosion and abrasion, reductions in weight and friction, enhanced durability, and product cost savings. For automobiles, this leads to increased fuel economy and lower emissions. Millions of engine cylinder bores per year are coated using the PTWA thermal spray process. To ensure optimal surface coatings, it is vital to monitor the process variables. Although some process monitoring already exists in current production, new technological advancements allow for additional variables to be monitored. Arc voltage is of particular importance as it can be viewed real-time in situ to the PTWA process to determine the curvature of the feedstock wire. Straight wire is ideal for achieving peak system performance. If the wire has excessive curvature, it can lead to out-of-tolerance conditions that detrimentally affect the quality of the surface coating. Therefore, in-situ monitoring of wire curvature is both desirable and necessary for producing the highest quality PTWA thermal spray coatings possible.

Wire-arc spraying is particularly used for large-area coatings due to the high cost efficiency of the process but is also characterized by strong fluctuations. Nowadays, a costly and time-consuming inspection is required after coating in order to identify and eliminate possible coating defects caused by the process instability. Therefore, a sensor unit with seven channels is established, which realizes an in situ monitoring of the process. The voltage and current sensors are analyzed in detail within this work. Additionally, a variation of the process parameters voltage and wire feed was used to compare the data of a stable and an instable process regarding the arc stability. For a deeper understanding of the process and its performance, the surface is characterized by confocal laser scanning microscopy and cross-sections are investigated by SEM as well as light microscopy. The new and so far, unique sensor unit is successfully established for the current and the voltage sensor on the wire-arc spraying process. The in situ recording identifies fluctuations of the spraying process. Anomalies of the current I were detected before the break down of the arc occurred. The parameter variation showed an influence on the coating properties. A higher voltage results in a denser coating structure.

Developing a cost-effective fabrication method for devices containing metal channels with surface features on the submillimeter scale is essential for the development of novel, high efficiency micro-reactors and heat sinks. Traditional methods are limited by their high cost, low geometric accuracy, high energy consumption, and long processing times. This study presents a low-cost additive manufacturing method using twin wire arc spray to make surface features at the sub-millimeter scale. Water-soluble polyvinyl alcohol (PVA) paste is first placed onto a mold containing a negative of the desired surface features and allowed to cure. The cured PVA is removed from the negative and metal sprayed onto its surface. The deposited metal film was backed by epoxy for added rigidity. The PVA paste was then dissolved in a water bath, resulting in a metal surface with the surface features of the mold. Surface features with length scales as small as 200 μm were reproduced. Coating delamination was prevented by minimizing the temperature of the substrate during spraying by increasing the standoff distance and scanning speed of the spray torch.

Additive manufacturing with metal powders enables a high degree of design diversity and an enormous material flexibility for components. The development of new products using special alloys requires just a small amount of powder. Therefore, a wire arc spraying process using nitrogen is applied for powder production by atomizing. The remaining oxygen content, the nitrogen temperature and pressure in the atomizing chamber are monitored to ensure consistent quality. The power source enables direct current (DC) and alternating current (AC). Further parameters like basic current Iground, pulse current Ipulse, pulse duration tpulse, impulse frequency fpulse and alternating current frequency fAC can be varied. On the process side, the following parameters are recorded during the tests: current, voltage, wire feed speed and flow rate of the atomizing gas as well as oxygen content and temperature inside the spray chamber. These parameters have an influence on particle size and composition. The aim is to influence the melting behavior by electrical and other process parameters. The investigations are carried out on solid wires made of an iron-based alloy EN ISO 14341-A: G42 4 M21/2 C1 3 Si1, AWS A 5.18: ER 70-6.

With an increasing demand for lower fuel consumption of different means of transportation, the demand for lightweight construction materials is rising. In this frame, usually metallic parts can be replaced by components consisting of fiberreinforced plastics. On the other hand, the components lose their electromagnetic field (EMF) shielding properties, which are required for many applications such as housings for electrical components. This issue can be solved by applying electrically conductive foils or meshes, often by a manual process that increases the time of production and process. In this publication, the application and parameter influence of thermally sprayed electrically conductive coatings for EMFshielding applications is discussed. Laser structuring is used as a novel surface preparation process, for the subsequent thermal spray process. The influence of the used laser-parameters is discussed accordingly. The coatings are applied by the wire-arc spray with Zinc feedstock as well as the atmospheric plasma spray (APS) process with Copper feedstock. It was found that coating properties such as adhesion strength, EMF-shield strength as well as electrical properties are provided by the proposed technology.

Miniaturization and performance improvements of electronic devices in recent decades have significantly increased heat dissipation rates. To overcome this, researchers have developed heat sinks with miniature fluid channels to maintain small device footprints with increased heat transfer performance. These channels are often fabricated using either subtractive fabrication methods, such as etching or micro-milling, or additive methods such as direct metal laser sintering (DMLS). These methods are limited by their long processing times, low geometric accuracy, or high cost. To overcome these limitations, a novel additive manufacturing method is developed using twin wire-arc spray. Wire-arc spray was used to build complex aluminum structures with length scales varying from 0.5 mm to 74 mm. Surface structures were built on a metal plate by spraying aluminum through a 3D printed polymer mask. Internal flow passages were made by filling surface channels with a water-soluble polyvinyl alcohol (PVA) paste that was allowed to harden, spraying metal over it, and then dissolving the PVA. The influence of wire-arc spray process parameters, such as standoff distance and scanning speed, on coating solid PVA with aluminum, were also investigated.

Whenever large amounts of liquids or gases have to be transported over long distances, steel pipelines are used. They supply industry with raw materials, guarantee drinking water supplies to large cities, and convey energy sources around the globe. Despite the most stringent safety regulations, pipelines regularly suffer damage and leaks. Severe environmental pollution occurs when oil or gas pipelines, in particular, are damaged. In the case of both onshore and offshore pipelines, decontaminating the affected areas involves a great deal of time, effort, and cost. Moreover, in most cases the contamination cannot be eliminated completely. There are various reasons for damaged pipelines. Corrosion poses one of the greatest challenges here, and this can be influenced by the pipeline owners. There is a need for safe and reliable corrosion protection, and this is set to grow over the coming years. Based on current market data, between 13 and 18 million tons of line pipe were delivered in the years 2015 to 2020. This corresponds to a pipeline length of approx. 86,000 km per year. The objective of this paper is to illustrate why the corrosion protection currently used fails to work in some cases. It also aims to show how thermal coating can improve corrosion protection and what requirements its technical implementation must fulfil. To this end, line pipe is presented in the next chapter. Common standards and manufacturing processes are introduced. The third chapter outlines current corrosion protection measures. Moreover, weak points are analyzed by looking at damage that has already occurred. The requirements for thermal coating are determined based on this.

Surface treatments and coatings are widely used to protect components from wear and corrosion. Of all available methods, thermal spraying is arguably the most versatile with regard to coating material and morphology. Surface roughness and porosity can be adjusted in a wide range depending on the requirements. However, as-sprayed coating surfaces inevitably exhibit a certain roughness necessitating post-treatment if a smooth surface is required. The surface roughness of thermal spray coatings is usually determined by the used powder fraction and the particles’ melting degree. Using wires as feedstock material allows for a certain influence on the particle size distribution by adjusting process parameters. In this study, the influence of nozzle geometry and atomizing gas pressure on coating quality, surface roughness and cost-efficient post-treatments of wire-arc sprayed Fe-based alloys with a wide hardness-range is investigated. To allow for easy transfer to real components, the sample geometry is based on real world examples of coatings for new components and repair of worn parts. Using adapted process parameters and air-flow, the surface roughness could be decreased to allow for a less time-consuming post-treatment by grinding. Especially in repair coatings for large area applications requiring a smooth surface finish, significant runtime and cost reductions are feasible.

Despite their light weight, 2.3 times lighter than Al, polymers are limited to application with low thermal, wear, and abrasion demands. The enhancement of the functional surfaces of the polymers using thermal spraying techniques is a challenging task due to the thermal degradation of polymers, the low wettability, and the disparate atomic properties. The twin-wire arc spraying (TWAS) process comprises two contradictory features. Almost all spraying particles are in a molten state on the one hand, and on the other hand, the spray plume has the lowest heat output among the different thermal spraying techniques. Therefore, it is a promising spraying technique for the required surface improvement. The surface of the 3D-printed parts was metalized using two successive layers. The first layer is a TWAS coating made of low-melting ZnAl 4 to avoid thermal degradation and provide a bond coat. The topcoat is also applied using a TWAS process and was made out of Ni-WC-Co as cored wires. The top hard coating has improved the wear resistance of the polymers by 14.6 times. The erosion of the coated and uncoated specimens was determined using a low-pressure cold gas spray gun. Ni-WC-Co coating led to more than five times higher erosion resistance.

Viruses and microbial pathogens can survive for hours on fabrics. This paper reports that copper-doping of natural and synthetic fabrics inactivates, within minutes, a human COVID surrogate pathogen. The fabric is embedded with copper particles by twin-wire arc thermal spray. The long-lasting fabric surface simultaneously provides good breathability, it is scalable and cost-effective. Virucidal activity is not affected by repeated washing of the fabric. Importantly, copper-embedded material will provide effective protection against all classes of pathogens, regardless of their mutation rates and infection strategies. It also can provide protection against all classes of pathogens, regardless of their mutation rates in industrial and residential filters.

Metals were deposited on components made by 3-D printing with polyvinyl alcohol (PVA), a water-soluble polymer. The polymer was then dissolved, leaving a metal layer whose surface topography was the negative of that of the polymer. This is a rapid and low-cost alternative to 3D printing directly using metal, but to succeed it is essential for the sprayed metal to adhere to the polymer substrate. Tests were done in which aluminum and copper were sprayed using a twin-wire arc spray system onto 3D printed coupons, 50 mm x 50 mm in size, made from polylactic acid (PLA), PLA mixed with metal (aluminum, copper) or carbon fiber, and PVA. Adhesion depended on substrate roughness (minimum 1-2 μm) and substrate temperature (above the glass transition temperature but below the melting temperature of the polymer). It was shown that surface features could be made with high resolution on metal components using this technique.

Biofouling has been persisting as a worldwide problem due to the difficulties in finding efficient environment-friendly antifouling coatings for long-term applications. Developing novel coatings with desired antifouling properties has been one of the research goals for surface coating community. Recently hydrogel coating was proposed to serve as antifouling layer, for it offers the advantages of the ease of incorporating green biocides, and resisting attachment of microorganisms by its soft surface. Yet poor adhesion of the hydrogel on steel surfaces is a big concern. In this study, porous matrix aluminum coatings were fabricated by cored wire arc spray, and the sizes of the pores in the aluminum (Al) coatings were controlled by altering the size of the cored powder of sodium chloride. Silicone hydrogel was further deposited on the porous coating. The hydrogel penetrated into the open pores of the porous Al coatings, and the porous Al structure significantly enhanced the adhesion of the hydrogel. In addition, hydrogel coating exhibited very encouraging antifouling properties.

Twin wire arc is a commonly used thermal spray technology for application of steel coatings to cast iron components. Hardness and adhesion strength are critical properties of such coatings, and significant research is available reporting these properties. However, residual stresses and the anisotropic structure of the coatings leads to significantly different behavior in bending applications than in the purely tensile loading of the standard adhesion test. In addition, microstructural features that are controlled by certain process parameters during deposition of the coating can have a significant effect on these properties. This work seeks to relate the hardness and pull-off adhesion strength to the coating microstructure, and to assess the related bending strength and failure mode. Comparisons between bend tests and pull-off adhesion tests show significant differences to consider when evaluating twin wire arc coatings.

Assemblies containing fiber-reinforced plastic (FRP) and metal parts are typically fastened together via mechanical joining or adhesive bonding. Mechanical joining processes tend to weaken FRP parts by cutting fibers, while adhesives require long cures and often lead to inseparable material compounds. This paper evaluates a new joining method in which plastic parts are laser treated, then metallized via wire-arc spraying, and finally soldered to mating metal parts using a low-temperature process. Due to the effective increase in interface area resulting from laser structuring, bond strengths of up to 15.5 MPa can be achieved.

Wire atomization processes used to make refractory and high temperature alloy powders are relatively expensive due to the cost of feedstock, energy, and gas. A new process based on Transferred Arc Wire Atomization technology, however, has the potential to overcome these problems. This paper introduces the innovative process which, in combination with hydrogen generation, presents new opportunities for several alloys that can be more easily processed by plasma wire atomization. The new approach shows promise to reduce both fixed and variable costs for certain refractory and high temperature materials.