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.

In cold spray, optimum process conditions to accelerate particles vary with different densities and melting temperatures of the materials. Therefore, material-specific nozzle designs are required. In the present study, a nozzle geometry optimization concept based on 3D-CFD simulations was developed to provide a specific nozzle design for a given material. Al6061 and pure copper with mean particle diameters of 40 μm were taken as examples. Together with a design of experiments (DoE) approach, the model seeks for the optimal nozzle geometry. In order to reach the highest particle velocity prior to impact upon the substrate, different geometry parameters were varied, such as the nozzle throat cross section, the aspect ratio, and the nozzle divergent section length. The process gas was nitrogen with set stagnation pressure and temperature of 50 bars and 500 °C. For both materials, the simulation identified nozzle divergent section length as the most influential parameter, followed by the throat cross-section. The aspect ratio must be tuned to avoid over expansion of the gas in the nozzle.

In our laboratory, we have developed a method to simultaneously inject different powders from the central axis direction and radial direction of the cold spray nozzle and are producing a composite coating by this method. In the previous research of our laboratory, an Al-12Si alloy coating with excellent wear resistance was produced by micro-forging assisted cold spray using the simultaneous nozzle injection method of powder in the axial and radial directions. Here, Al- 12Si alloy, which has excellent wear resistance, was used for the coating-formed particles, and stainless steel was used for the micro-forging particles. However, because the micro-forging particles were hollow, they remained in the coating. In this paper, we evaluated the influence of increasing the mixing ratio of micro-forging particles instead of solid (no holes) micro-forging particles on the coating structure. At the same time, the behaviors of particles by computational fluid dynamics are also investigated.

A computational fluid dynamics model for understanding the HVAF process and the influence of the process parameters on the particle flight properties is investigated. Achieving this objective involves a novel approach to modeling the HVAF process with pressure inlet boundary conditions and integration of the mixing chamber. The study comprises the prediction of the flow fields described by a set of equations consisting of continuity, momentum, energy, and species transport. These equations are then solved with realizable k-ε turbulence model, a two-step chemistry model and eddy dissipation model to simulate the combustion reaction. Consequently, the interaction between the CoNiCrAlY alloy particles and the flow is modeled using a Lagrangian approach considering the forces acting on the particles and the heat transfer. The results show that the combustion chamber pressure is mainly affected by the compressed air and propane parameters. Furthermore, the flight behavior of the smaller particles is significantly influenced by the gas flow, while the larger particles tend to maintain their momentum and energy. Through the simulation model, an in-depth process understanding of the HVAF process can be achieved. More importantly, the model can be used as a tool for efficient process development.

Thermal spraying is a complex physical process consisting of three main sub-systems: flame/plume generation, powder/flame/plume interaction and coating build-up. While mathematical and CFD models provide valuable insight about the individual modules of a thermal spray process, it is very difficult to gain overall insight of the whole process and dependencies between different inputs and outputs using mathematical and CFD analysis, due to very complex and interconnected nature of the thermal spray process. In this work, a sophisticated experiment has been conducted to collect enough data for the sake of developing data-driven model of a plasma spray process. Metco 204 powder feedstock material and F4 gun have been used. An optimized number of data samples has been chosen by applying common industrial input parameters in the experiment. The developed neural network model is able to predict the coating quality parameters with acceptable average accuracy of above 90% on test data by considering all relevant measurement error deviations of the process analysis methods. A sophisticated user-interface has been developed to enable the use of the model for coating parameter development as well as the designing recipe for target coating characteristics. The developed model can be used for different purposes: parameter development, off-line coating quality control, and eventually adaptive coating control.

In a DC plasma spray torch, the plasma-forming gas is the most intensively heated and accelerated at the cathode arc attachment due to the very high electric current density at this location. A proper prediction of the cathode arc attachment is, therefore, essential for understanding the plasma jet formation and cathode operation. However, numerical studies of the cathode arc attachment mostly deal with transferred arcs or conventional plasma torches with tapered cathodes. In this study, a 3-D time-dependent and two-temperature model of electric arc combined with a cathode sheath model is applied to the commercial cascaded-anode plasma torch SinplexPro. The model is used to investigate the effect of the cathode sheath model and bidirectional cathode-plasma coupling on the predicted cathode arc attachment and plasma flow. The model of the plasma-cathode interface takes into account the non-equilibrium spacecharge sheath to establish the thermal and electric current balance at the interface. The radial profiles of cathode sheath parameters (voltage drop, electron temperature at the interface, Schottky reduction of the work function) were computed on the surface of the cathode tip and used at the cathode-plasma interface in the model of plasma torch operation. The latter is developed in the open-source CFD software Code_Saturne. It makes it possible to calculate the flow fields inside and outside the plasma torch as well as the enthalpy and electromagnetic fields in the gas phase and electrodes. This study shows that the cathode sheath model results in a higher constriction of the cathode arc attachment, more plausible cathode surface temperature distribution, more reliable prediction of the torch voltage, cooling loss, and more consistent thermal balance in the torch.

MCrAlX powder compositions (M=Ni, Co and X=Y, Hf, Si or combination) are often thermally sprayed (TS) via vacuum plasma spray (VPS), low pressure plasma spray (LPPS) or high velocity oxy-fuel (HVOF) to produce high temperature oxidation and hot corrosion resistant bond coats (BC) for thermal barrier coatings (TBCs). Cold spray (CS) technology is currently considered as a promising alternative to the traditional TS solutions having the advantage of delivering oxide-free and very dense metallic coatings at relatively lower costs compared to VPS and LPPS. Here, we first present high-pressure CS deposition of NiCoCrAlY and NiCoCrAlYHfSi and discuss the influence of feedstock properties on the deposited BCs. CFD numerical simulation is employed to tailor the spray conditions based on the feedstock characteristics. Secondly, we present the laser assisted cold spray (LACS) deposition of NiCoCrAlYHfSi BCs using a low-pressure CS system. We show that LACS can be successfully used to deposit this particular powder while eliminating nozzle erosion and low deposition efficiency disadvantages observed during conventional CS. Lastly, high temperature isothermal oxidation of a TBC architecture having LACS BC is presented.

Segregating the convoluted effects of particle size, impact temperature and velocity on deposition behavior and adhesion is of utmost interest to the cold spray field. The current study aims to associate the particle impact behavior and adhesion to its in-flight characteristics by studying and decoupling the influence of particle size, temperature and velocity for single particle impacts and full coatings. Experimental results reveal that in-situ peening processes contribute to the adhesion at low impact temperature while particle velocity controls the adhesion/cohesion at increased particle impact temperatures. The benefits of both bonding mechanisms are discussed in terms of measured adhesion/cohesion, bend-to-break fracture surfaces, pseudoplasticity, deposition efficiency and critical velocity. Computational fluid dynamics (CFD) results provide individual particle trajectory, size, temperature and velocity, of successfully deposited particles, which have led to the observed signs of metallurgical bonding.

In the cold spray process, cross-sectional shape of the nozzle has a significant effect on spray pattern of coatings. The circular exit nozzle is parabolic in shape. So, spray pattern with the rectangular nozzle is wider than that with the circular spray nozzle. The goal of this investigation is to establish a design for the cold spray gun nozzle to gain more uniform spray profile of coatings. We have investigated the influence of expansion ratio, nozzle total length and the ratio of nozzle length of divergent section and parallel section of rectangular nozzle on behaviors of gas and particle by the computational fluid dynamics (CFD) in high pressure cold spraying. We have studied copper particles so far. In this study, we will examine aluminum particles. First, we investigate the influence of the size and shape of the rectangular section nozzle on the velocity, temperature, and particle distribution of aluminum particles by CFD. After that, the rectangular section nozzles were fabricated and coating formation experiments were conducted, spray patterns and coating cross-sectional structures were observed, and coating adhesion was also evaluated. The nozzle material was polybenzimidazole resin, which is difficult for aluminum particles to attach to nozzle walls.

The generation of a high velocity carrier gas flow for cold metal particle applications is addressed, with specific focus on titanium cold spraying. The high hardness of this material makes cold spraying titanium difficult to achieve by industry standard nozzles. The redesign of a commercial conical convergent-divergent cold spray nozzle is achieved by the application of aerospace design codes, based on the Method of Characteristics, towards producing a more isentropic expansion by contouring the nozzle walls. Steady three-dimensional RANS SST k-ω simulations of nitrogen are coupled two-way to particle parcel tracking in the Lagrangian frame of reference. The new contoured nozzle is found to produce higher particle velocities with greater radial spread, when operated at the same conditions/cost of operation as the commercial nozzle. These numerical results have shown the potential for extending cold spray to high density and low ductility particles by relatively minor rig modifications, through an effective synergy between gas dynamics and material science.

In this paper, the phenomenological behaviour of gas flow and particles motion during cold spraying has been studied. Observations of particles behaviour show two features: a uniform jet over a short distance ahead of the nozzle exit and then, a progressive dispersion. These behaviours are explained using a computational analysis based on a direct numerical simulation of the gas flow and the kinematic interactions with the particles. The CFD computation demonstrates that the gas stream starts to be unstable inside the nozzle with more turbulence as it moves towards the exit of the nozzle. The flow is self-oscillated along the flow direction and drives the motion of the Cu particles outside the nozzle. The zone of gas flow instability does correspond to the zone of experimental particle dispersion. Outside the nozzle, the particles form a straight jet over a certain distance that corresponds to the zone of the experimental uniform particles jet. Then, they are deviated and become more and more dispersed towards a very sparse jet along the flow direction. This phenomenon is explained by a Magnus lift force that deviates the particles trajectory when the gas flow becomes highly turbulent while developing a vorticity shedding.

Instabilities and fluctuations of the plasma jet can have a significant influence on the particle in-flight temperatures and velocities, thus affecting the properties of plasma sprayed coatings. Presented in this paper is a novel method for capturing the effects particles are exposed to in the plasma spraying process. High-speed camera images of a plasma jet generated by a cascaded three cathode plasma generator (TriplexPro-210) are recorded for varying operating conditions. The images are processed using the inverse Abel transform. This transformation accounts for the fact that the images represent a 2-D projection and generates correct intensity values of the plasma jet images. These images are then combined with particle tracks resulting from CFD simulations of the plasma jet to match the particles path with the recorded plasma jet. This new method allows a precise description of the plasma intensity experienced by individual particles with a high temporal resolution. The results show a high sensitivity of the method, it can even detect the influence of the plasma jet originating from the cascaded triple arc plasma generator, which is considered as rather stable, on the particles.

Industrialization of cold spray brings along the questions of cost and time efficiency of various spray procedures. In this work, high rate deposition of tantalum was studied by producing coating specimens where the powder to helium mass flow rate varied from 5% to 14%. Quasi-1D fluid simulations predict a minimal effect of increased powder stream loading on particle impact velocity and temperature over those ranges, but the cost varies substantially. The experimental specimens, examined by using optical micrographs, porosity measurements, and hardness tests, show no discernable differences in the deposited samples. The increased stream loading rate, however, helped reduce the time required for processing the same amount of tantalum by a factor of three using identical helium spray conditions.

This study compares the performance of circular and rectangular cold spray nozzles based on numerical simulations and experimental results. It shows how nozzle geometry and gas pressure affect the velocity and temperature of copper particles at various points in their travel. The goal of the investigation is to establish a nozzle design that achieves a uniform spray pattern with suitable particle impact velocity for the materials and temperatures involved. It was found that a rectangular nozzle with an expansion ratio in the range of 11-12 can provide a more uniform particle velocity with high deposition efficiency at a reasonable gas pressure.

Thermal barrier coatings are generally produced one of two ways, depending on the thermomechanical loading expected. This study assesses an alternative approach in which the output of an air plasma torch is directed through two chambers connected by an expansion nozzle. In the first chamber, the particles evaporate under high pressure and temperature conditions. The vapor then passes through a supersonic nozzle into a low-pressure chamber where it condenses on the target substrate. A number of models are developed and used in order to assess the effects of process geometry and operating conditions on gas flows, powder vaporization efficiency, and nucleation and growth kinetics. Numerical simulations also informed various design decisions such as the length of the high-pressure chamber and the diameter of the expansion nozzle.

In this paper, the principles of computational fluid dynamics are used to simulate the complex gas flows in the cylinder bore of an automotive engine during internal-diameter twin-wire arc spraying. A number of experiments are conducted as well and the results are presented and analyzed in order to optimize the properties of the coating. The combination of simulation and experiments led to the development of a process that achieves uniform layer adhesion strength over the length of the cylinder bore.

Common issues such as ice formation on wind turbine blades and lightning strikes on airplanes can be mitigated by metallizing polymers and composites used on the outer surface of the component. Cold gas dynamic spray is a novel process that has the potential to be used for metallization of polymer and composite surfaces to produce electrically and/or thermally conductive components. In this study, mixed Cu-Zn and Al-Zn feedstock powders were deposited onto polypropylene and nylon-6 substrates to investigate the viability of metallizing nonmetallic surfaces using a commercially available low-pressure cold spray process. The behavior of the individual metallic particles upon impact on the polymers and the deformation of the substrate were characterized by coating the two feedstock powders onto a nylon-6 substrate over a wide temperature range. The Cu-Zn coating was deposited in thicknesses up to 1 mm onto the nylon-6 substrate using optimized parameters. To understand the deposition of the metallic powder onto the polymers, the process was modeled using computational fluid dynamics methods. The correlation of the gas and particle modeling with examination of the coating microstructure highlighted the major importance of the particle velocity during cold spray deposition.

In cold spray, 5-150 μm particles (of metal, ceramic, composite, and other materials) are accelerated to supersonic velocities through a deLaval nozzle with an inert gas (generally He or N 2 ) that can reach 1000 °C. In the process, the gas jet impingement on the target and the extreme plastic deformation of impacting particles cause heat generation in the coating layers and the substrate. The heat generation has been argued to cause residual stress, which may cause coating-substrate delamination. In this study, heat generation due to gas impingement and particle plastic deformation has been predicted from CFD and FEA simulations, respectively. Furthermore, a finite volume method has been presented for transiently simulating the coating buildup and bulk heat generation in the coating and the substrate. The model is intended to assist researchers understand thermal affects in the coating process and help design more informed coating patterns to reduce negative thermal effects.

The dynamic properties and thermal history of FeAl particles were estimated and assessed in this study. First, parameters of the detonation process for the investigated mixture were calculated using a thermochemical code. Next, the motion parameters and thermal history of the analyzed powder particles were assessed using computational fluid dynamics software and algorithms developed by the investigators. The appropriate models allowed for determination of melted volume (mass) fraction of a certain analyzed single particles that have diameters ranging from 10 to 160 μm. The results show that only the smallest particles melt under the investigated conditions. Moreover, the estimated radial distribution of the temperature inside the particles is almost homogeneous due to the relatively high FeAl thermal conductivity and relatively low thermal conductance of surface heat transfer. The calculated particle terminal velocity was compared to experimental data and to data from previous studies in the literature to determine the accordance of results among the data sets.

In times of duality of combustion engine and electric motor propulsion the automotive industry is developing both powertrain systems. Weight reduction and enhancement of efficiency plays a vital role in the conception of combustion engine for passenger cars. The thermal spray technology therefore is trend-setting as it achieves both aims. GROB-WERKE have, as reported previously, developed and integrated their GTS (GROB Thermal Spray) process for steel deposits in aluminum cylinder bores into their production lines. Further effort was now made to improve performance and versatility. The application of measurement and simulation technics hand in hand with extensive experimental investigation in spray deposit diagnostics as well as plasma and particle jet analysis led to highly developed and advanced deposit microstructure and cylinder bore topographies. Complex and extensive CFD (Computational Fluid Dynamics) simulation of the gas and particle flow gave the thermal spray process the highest performance, efficiency and product cleanliness.