Plasma spraying is a key industrial coating process that exhibits intricate nonlinear interactions among process parameters. This complexity makes accurate predictions of particle properties, which greatly affect process behavior, very challenging. Specifically, particle velocities and temperatures profoundly impact coating quality and process efficiency. Conventional methods often require empirical correlations and extensive parameter tuning due to their limited ability to capture the underlying physics within this intricate system. This study introduces Physics-Informed Neural Networks (PINNs) as a solution. By seamlessly integrating known physical laws and constraints directly into the model architecture, PINNs offer the potential to learn the underlying physics of the system. For comparison, Artificial Neural Networks (ANNs) are also developed. Computational Fluid Dynamics (CFD) simulations of a plasma generator and plasma jet model provide data to train both ANN and PINN models. The study reveals an improvement in particle velocity prediction through the proposed PINN model, demonstrating its capability to handle complex relationships. However, challenges arise in predicting particle temperature, warranting further investigation. The developed models can aid in optimizing the plasma spraying process by predicting essential particle properties and guiding necessary process adjustments to enhance coating quality.

Previous studies have shown that gas shrouding is an effective means for controlling oxidation during HVOF spraying. In this present work, the authors attach a gas shroud to an oxyfuel torch with a longer barrel to further investigate the correlation between the state of HVOF sprayed particles and the density and oxygen content of the resulting layers. It is shown that with gas shielding, extended barrel length, and optimized spraying parameters, it is possible to accelerate powder particles to a velocity of over 750 m/sec with maintaining a high molten fraction, thereby producing very dense (zero porosity) stainless steel layers with oxygen contents less than 0.2% by weight. Paper includes a German-language abstract.

The heat and momentum transfer of the plasma to the injected particles is an important issue in coating formation during plasma spraying. In this study, the plasma temperature and velocity of a Triplex-I torch was measured by means of an enthalpy probe system. Additionally, the properties of injected yttria-stabilized-zirconia powder of a fine sized fraction were recorded spatially resolved by using a DPV2000 system. The plasma temperature and velocity are decreasing by increasing the distance from 45 to 60 mm with respect to the torch exit by approximately 50% from initially 6200°C and 400 m/s, respectively. In contrast, the particles gain temperature up to the melting point at 70 mm stand-off distance as well as the velocity rises up to its highest value of 115 m/s at the maximum flow rate of the particles. Both, plasma and particle characteristics were used to obtain a deeper insight on heat- and momentum transfer of the plasma jet to the single particles.

This paper investigates the influence of process parameters on plasma sprayed particles. Through simulations, the authors show that particle velocity is largely a function of trajectory, which is influenced by plasma composition, powder properties, injection velocity, particle size distribution, and kinetic energy. Depending on kinetic energy, the particles are deflected by the high viscous region around the flow core, they enter the core, or they pass through it into the slow outer flow on the opposite side. Paper includes a German-language abstract.

This paper shows how in-flight particle diagnostics can be used to optimize parameter sets for new layer materials and to detect drift in the control of thermal spraying lines. It describes the equipment and methods used to measure the temperature, velocity, and diameter of spray particles in a plasma jet and explains how torch current, plasma gas composition, carrier and total gas flow, and stand-off distance are varied according to a statistical design plan to determine their effect. The results are presented in the form of process maps and data plots, from which several conclusions are drawn. Paper includes a German-language abstract.

Thermal spray technology became established in various parts of industry (e.g. aircraft industry, medical industry etc.). Some of the applications are highly sensitive, therefore the coating quality plays an important role. Most of the common quality control methods are based on destructive testing methods which are undesirable for economical reasons. In recent years the interest in non-destructive online measurement methods increased and still is growing. More detailed knowledge of the relationship between process parameters can help to improve the coating quality standards and to understand different phenomena in thermal spraying. This will make online process control possible and improves the acceptance of thermal spray technology. In this paper results of fundamental studies on the atmospheric plasma spraying process (APS) are presented. Al 2 O 3 and NiCr powder were sprayed as model materials. In the experiments modem on-line monitoring systems were used to investigate the entire process from gun parameters to the coating quality. The faces in this paper are set on investigations of the in-flight properties of spray particles with the particle sensor DPV 2000 and their relationship with resulting coating properties. A method will be presented to extract characteristic values (velocity and temperature) out of the spray process with DPV 2000. With this method the APS-process was monitored and process parameters were correlated with main coating properties.

Demands on functional coatings with high dimensional accuracy and high surface quality has led to increasing interest in processing of very fine powder grades in a particle size range < 25 µm. Fine powders are not only showing a distinct potential for application of thin and dimensionally accurate coatings, but are also very promising for the production of dense and homogeneous coatings with improved mechanical properties. The large specific surface of fine powders is allowing for relatively low thermal energy levels that are introduced into the process. Nevertheless this also requires a very sensitive temperature control, to prevent overheating of the particles. The reduction of the thermal energy level is resulting in significant advantages particularly for the usability of the HVOF process for coating of inner diameters. Within this work in-flight particle properties of ultrafine carbide powders were analyzed. The studied HVOF process allows the adjustment of a broad parameter range by utilization of a hydrogen stabilized liquid fuel combustion process. A conventional straight nozzle type as well as a curved nozzle for internal spraying was studied. For a further assessment of the potential of ultrafine carbide powders also spray trials with a plasma spraying system have been made.

This work investigates the effect of atmospheric plasma spraying (APS) parameters on in-flight particle properties, splat morphology, and coating microstructure for conventional and nano-size YSZ powders. Particle temperature and velocity were measured using a dual-slit velocimeter and individual splats and coating microstructures were examined in a scanning electron microscope. The results show that total porosity increases with decreasing arc current and increasing stand-off distance and that conventional powder coatings have higher total porosity at higher arc currents than coatings made from nanopowder. The effect of substrate temperature on splat formation was also assessed. Splat flattening and circularity increase with increasing substrate temperature, particularly for nanopowders.

The triplex-torch design providing three stable arcs in power and geometry promises a stable, quasi-laminar plasma jet leading to an uniform plasma and thus an uniform particle distribution. Additionally, the three powder injectors lead to an extended powder feed rate, resulting in a lower spraying time. This paper deals with particle properties of YSZ (SM 204NS) with respect to their injection location and powder feed rate and the resulting coating microstructure and porosity levels. Concerning the injection conditions, the three powder jets can be clearly identified. Their location depends on the spraying distance and less pronounced on the injection velocity. Interestingly, if the different powder-sizes are grouped and the jet cross-section is plotted for the different size cuts, the position of each size cut varies. Thus, a local separation of the powder takes place in the jet. The powder feed rate was varied from 30 to 320 g/min. Accordingly to this variation, the particles mean temperature was lowered from 3050°C down to 2650°C, and the velocity values dropped from 230 m/s to 155 m/s. Regarding the achieved coating thickness, up to a powder feed rate of approximately 210 g/min the thickness is increasing with no dramatic change in the porosity values. More powder does not lead to a thicker coating but results in a significantly higher porosity. Moreover, the microstructure of the coatings obtained by using a higher feed rate exhibits more segmentation cracks.

During plasma spraying in-flight particle characteristics are influenced by the many operating parameters associated with the deposition process. The distinctive temperature and velocity signals given by particles as they exit the plasma torch can be used to develop processing maps for defining the optimal operating envelope. Knowing the temperature and velocity history of the particles, the evolution of the microstructure, the amount of porosity and the phase composition can potentially be predicted. In this paper, the relationship of system parameters (stand-off distance, torch power, plasma gas composition and process gas flow) was correlated to in-flight particle characteristics of yttria stabilized zirconia and compared to the resulting coating features such as thickness, microstructure, porosity and phase composition. The appearance of the coating (i.e., color) was also compared after the deposition process. Yttria stabilized zirconia was deposited on grit blasted samples using an F4 (Sulzer Metco) plasma torch. Before depositing each sample on the substrate, the particle properties were measured at the desired stand off distance perpendicular to the particle jet covering an area of 18x18 mm 2 using the Tecnar DPV2000 inflight particle analyzer. The coatings were cross-sectioned for microstructure analysis, thickness measurements and deposition efficiency. Free standing films were used for mercury intrusion porosimetry. Grey levels of the coatings were obtained by optical microscopy and subsequent digital image recording. X-ray-diffraction analysis was also used to obtain the phase composition. Results showed that different particle temperature and velocity conditions lead to specific porosity and varying colors of the deposit. The color of the deposit was correlated directly to the amount of monoclinic phase in the as-deposit material.

Numerous factors, such as the spray parameters and non-predictable conditions, during the spraying process influence the properties of thermally sprayed coatings. However, the condition of the particles at the moment of impact on the substrate is the most crucial factor for the morphology and the mechanical properties of a coating. Thus, nowadays particle analyzing systems are employed in order to explain the relation between the process parameters and the properties of a layer. Yet, modeling of thermal spray processes is conducted disregarding particle parameters and only correlating process parameters with layer properties. This article presents a new approach on process modeling, for relating spray parameters to particle-inflight conditions. The modeling of the particle properties in relation to the process parameters shall allow conducting targeted adjustments during the running process, to optimize particle properties. This method will enable to influence coating properties during the spraying process, eliminating the influence of unpredictable environmental or process-related disturbances. In a series of experiments, spray beam properties were measured in an HVOF thermal spray process with agglomerated and sintered WC-Co powder. Spray parameters were correlated to the particle-in-flight conditions, which were measured by utilizing two particle analyzing systems.

Plasma sprayed MCrAlY bondcoats play a major role in thermal barrier coatings. During service, oxide forms on both sides of the bond coat and must be minimized to prevent coating failures. Along with powder chemistry, coating microstructure significantly influences oxide growth. It is known that both coating microstructure and coating strength are strongly related to plasma spraying parameters. This present work examines the effect of inflight particle properties on the adhesion strength and microstructure of NiCrAlY and NiCoCrAlY bondcoats. The relation between particle velocity and temperature and coating properties is particularly important. Relatively small changes in spray parameters such as arc current and gas flows can have a major impact on sprayed particles and consequently coating microstructure. Through online control of particle states it is expected that the quality of plasma-sprayed MCrAlY coatings can be significantly improved.

The plasma spraying process is controlled by various parameters that have an influence on powder particle velocities, temperatures and trajectories just before impact to the substrate. In order to fully utilize the thermal and kinetic energy of the plasma it is important to obtain information from these powder particle properties. In this work an intensified CCD camera has been used to detect in-flight particles in an atmospheric plasma spraying process. Plasma spraying was performed using fused and crushed AI2O3 powder. The powder carrier gas flow rate was varied during the spraying experiments. All the other deposition parameters were kept constant. Coatings produced using relatively new spraygun electrodes are compared with ones produced later with the same electrodes when they were worn out. The particle concentration is determined on a relative scale by the fraction of the area of a CCD camera frame covered by particle images. Further investigations necessary to clearify the relationship between the measured relative particle concentration and the true particle concentration are identified. The coatings are analyzed for wear resistance, degree of melting, deposition efficiency, hardness and porosity. The dependence of these coating properties on the relative particle concentration and the effect of electrode wear on the relative particle concentration are studied.

New developments in the field of thermal spraying systems (increased particle velocities, enhanced process stability) are leading to improved coating properties. At the same time innovations in the field of feedstock materials are supporting this trend. The combination of modern thermal spraying systems and new material concepts has led to a renaissance of Fe-based feedstocks. Using modern APS or HVOF systems, it is now possible to compete with classical materials for wear and corrosion applications like Ni basis (e.g. NiCrBSi) or metal matrix composites (MMC, e.g. WC/Co or Cr 3 C 2 /NiCr). The work described in this paper focuses on that combination and intends to give an analysis of the in-flight particle and spray jet properties achievable with two different modern thermal spraying systems (kerosene driven HVOF system K2, 3- cathodes APS system TriplexPro-200/-210) using Fe-based powders. The velocity fields are measured with the Laser Doppler Anemometry (LDA). Additionally, resulting coatings are analyzed metallographically with regard to their properties and a correlation with the particle in-flight properties is given. The experimental work is accompanied by computational fluid dynamics (CFD) simulations of spray jet and particle velocities, leading to a comprehensive analysis and characterization of the achievable particle properties with state-of-the-art HVOF and APS systems.

In the course of this investigation, thermal spraying with different fuel and shroud gas combinations was investigated in terms of its effect on the in-flight particle properties (temperature, velocity) and on the final coating properties (coating thickness, porosity, oxygen content and corrosion behaviour). Independent on the shroud gas, the particle in-flight temperature and velocity were highest when using ethylene as fuel gas and lowest when using propane. Methylene resulted in intermediate properties. The change in the shroud gas from air to nitrogen generally resulted in lower in-flight particle temperatures and also lower velocity. The coating properties in terms of porosity and oxygen content directly correlated to the particle in-flight properties. With decreasing velocity and increasing temperature, the porosity and the oxygen content increased, respectively. The corrosion behaviour of the nickel coatings was studied in 0.5 M sulfuric acid media by means of potentiodynamic polarization curves. Good corrosion properties were observed when methylene and air served as fuel gas and shroud gas, respectively.

Thermal spraying technology still suffers from a lack of reproducibility due to uncontrollable factors during the process. Current methods of process control by means of observing process parameters like gas- and powder flow are insufficient to guarantee a constant quality of coatings, while a direct analysis of the deposited layer is time- consuming and can only be conducted after the process. Furthermore, recently developed mathematical models which correlate process parameters to coating properties are not applicable for all materials. As the particles’ behavior during the process affects the coating properties, a direct process control by the observation of the particles seems expedient. This method is applicable on running processes and thus avoids defective production. In this study, HVOF spraying experiments were conducted. The in-flight particles’ behavior was investigated using an optical diagnostic system, while coating properties were analysed by metallographical methods.

Internal diameter (ID) coating by means of thermal spraying for the wear and corrosion protection of components is currently experiencing growing interest in science and industry. While high-kinetic spray processes (such as HVOF, HVAF or warm spraying) in combination with cermet materials (e.g. WC-Co or Cr3C2-NiCr) are well established for this purpose in traditional coating of external OD (outer diameter) surfaces, they have hardly been used in the ID (internal diameter) area so far. Even though a few special ID spray guns with compact design and low combustion energy are by now available on the market, only little is known about the effects and interactions of the spray parameters on the particle behavior and the coating properties. Due to the mentioned gun specifications and the usually required short spray distances for ID coating, fine spray powders < 15 μm must be used to ensure sufficient melting and acceleration of the particles. In this study warm spraying of fine WC-12Co powders (-10 + 2 μm) using a novel spray gun “ID RED” (Thermico, Germany) was investigated. Statistical design of experiments (DoE) was employed to analyze and to model the influence of varying spray parameter settings on the in-flight particle behavior and the corresponding coating properties.

Three different types of polyethylene powders were flame sprayed onto pre-heated steel substrate previously coated by electrostatic spray system with a thin epoxy primer layer. Properties of the polyethylene (PE) powders, including powder density, particle size and melt flow rate (MFR) were measured in order to study their influence on the mechanical properties of the coating. The spray experiments started with optimization of spraying parameters. The main variables were pre-heating temperature of the substrate, temperature increase during spraying (influenced by the spraying distance), and thickness of the PE coatings. The laboratory tests performed for the coatings were coating characterization by microscopy and mechanical testing. Porosity and thickness of the coatings were determined by optical and stereo microscopy studies from polished cross-sectional samples. Hardness, impact strength, peel strength, and adhesive strength of the coatings were also investigated. Also some hot water sinking and heat cycling tests were performed. As a result from the present studies it can be concluded that powder properties have great influence on the mechanical properties of the final coating.

The aim of this study was to compare different processes for a spraying NiCrBSi powder in order to understand how the coating properties are influenced by the particle characteristics. For that, three processes were tested: atmospheric plasma, HVOF and flame spraying. The plasma torch was a classical F4 gun from Sulzer-Metco, the HVOF gun was the CDS system manufactured by Sulzer-Metco and the flame spray gun was a Castolyn 8000 system. For each spraying process, the particles were analyzed using the DPV 2000 (Technar Ltd) at the distance corresponding to the coating build up. Particles velocity and temperature data were then correlated to the coating quality. Results indicate that the choice of the spraying technique induces important modifications in the coating properties in terms of adherence, porosity level, hardness and Young modulus. Changes in particle velocity and temperature are the key parameters determining the coating properties.

The present study aims to elaborate the particle in-flight behavior during plasma spraying and its significance in determining the microstructure and mechanical properties of plasma sprayed yttria partially stabilized zirconia (YPSZ) based thermal barrier coatings (TBCs). The as-sprayed YPSZ coatings were characterized in terms of the defects (such as porosity, unmelted particles, cracks and micro-cracks), hardness, elastic modulus and fracture toughness. The results showed that the total defects percentage, porosity, unmelted particles and crack content were found to decrease significantly with the improvement of temperature of in-flight particles. The mechanical properties were associated with the microstructure of these coatings, such as total defects, porosity, unmelted particles and cracks. It was confirmed that the mechanical properties, including hardness, elastic modulus and fracture toughness, notably enhanced with the total defects, porosity, unmelted particles and cracks decreased. The SAPS (supersonic atmospheric plasma spraying) coatings sprayed at 3401 } 3.76 °C and 482 ± 2.18 m/s and a spraying distance of 100 mm possessed the lowest microstructural defects percentage and the most favorable mechanical properties among the 15 coatings.