Since cold spray is widely considered as an additive manufacturing and damage repair technology, it is crucial to understand the coating build-up process and the temperature evolution. In this work, a 3D numerical model was developed to simulate the transient coating build-up process as well as the heat transfer in cold spray. By coupling the heat transfer with the ALE (Arbitrary Lagrangian–Eulerian) moving mesh and coating thickness model, this 3D model is able to investigate the temperature evolution of a coating which simultaneously grows according to the nozzle trajectory. The nozzle trajectory that represents the heat source and mass flux of particle impact is generated and simulated in the offline programming software RobotStudio. By assigning the results of coating thickness distribution, the simultaneous build-up of coating computational domain is achieved by ALE moving mesh method. The validation of the FEA (finite element analysis) model was carried out by measuring the coating surface temperature via an infrared imaging camera. With the proposed model, it is able to study the actual coating build-up process as well as the heat transfer phenomena, which may provide more insights for the application in additive manufacturing and damage repair.

Cold spraying consists in depositing a variety of metals as dense coatings onto metal surfaces. Indeed, copper, stainless steel, nickel, chromium, aluminum, cobalt, titanium, niobium and other metals can all be deposited, as well as metal alloys according to these base-metals and braze powders. The particle-substrate contact time, contact temperature and contact area upon impact are parameters influencing physico-chemical and mechanical bonds. The resultant bonding arose from plastic deformation and temperature at the interface which illustrates why metal coating cannot be sprayed onto rough ceramic substrates. Laser surface texturing has been used as prior treatment to create specific topography. Metal-ceramic has demonstrated a non-deformation of the substrate minimizing intimate bonds. Particle compressive states indicate anchoring mechanisms for laser textured surfaces. Consequently, cold spraying parameters depend on the target material and a methodology can be established with particle parameters (diameters, velocities, temperatures) and particle/substrate properties to adapt the surface topography. Mechanical adhesion is a key issue in cold spray process. As a result, laser surface texturing is a promising tool to adapt the surface to improve adhesion. Metallization process can be achieved.

The paper reports numerical simulation results of a direct current (DC) suspension plasma spray with an axial injection system. In the numerical modelling, a two-way coupled Eulerian-Lagrangian approach was employed to simulate plasma flow and suspension behavior. As effects of two-way interaction, momentum transfer and energy transfer were chosen. The plasma spray was assumed to have a rotationally symmetric, two-dimensional shape around the injection axis of suspensions (the central axis), and therefore the axisymmetric two-dimensional approximation was adopted in the numerical modelling. Working gas was pure argon and was supplied from both the anode-side and the cathode-side ports. A total volume flow rate of the working gas from anode and cathode was set to 46.5 slm. A feed rate of suspension was parametrically set to 0, 15, 25, or 35 g/min. Numerical results indicate that the temperature of a plasma hot-core region and the velocity of a plasma jet around the central axis drop more with increasing feed rate of suspension mainly because of a decrease in Joule heating with increasing it. The numerical results also suggest that the increase in feed rate of suspension leads to practically lengthening flight distance of suspensions required for completing evaporation process of disperse medium.

Traditional low-cost bulk materials are unable to fulfil the increasing requirements of actual technology and functional coatings – e.g. APS alumina coatings on aluminium substrates for tribological properties – are a suitable alternative. The development of new thermal sprayings is usually based in experimental procedures which involve long development times and high costs. Nowadays, numerical simulation allows the researcher a better understanding of thermal spray processes as well as reducing the time and cost for the optimization of processes, but it requires a deep insight into the physics of the phenomenon. The submodelling approach allows the researchers to work with a local model, a thin layer – just a few microns – on the metal substrate surface, and more realistic boundary conditions, which requires a little specialised knowledge. The current study involves the workflow to manage the modelling at piece scale, and the transfer and interpolation of boundary conditions in each scale. The coating is divided into several layers, which represent the successive splats deposited during the process, and the heat flow from the torch is modelled by radiation and convection. A code is implemented in order to generate the routine needed by the FEM software, in which the results are processed and interpolated for the subsequent submodel. Furthermore, the material plasticity is considered and several tests are performed in order to check the simulation results.

In this work, finite element modeling is used to investigate the influence of segmentation cracks on stress distribution and failure in thermal barrier coatings deposited by atmospheric plasma spraying. The results indicate that the presence of segmentation cracks does not improve thermal insulation, but it may be beneficial in regard to thermal shock resistance, depending on crack density, and residual stress around crack tips, depending on crack length. It may also improve strain tolerance, which is affected by crack density as well as length. A model is proposed to explain the mechanism of failure in thick TBCs exposed to thermal shock. Damage caused by thermal shock can be attributed to the propagation of segmentation cracks and the formation of horizontal cracks at the bond coat-topcoat interface.

This study employs numerical simulations to investigate the effect of pulsed electron-beam treatments on the porosity of plasma-sprayed cermet coatings. Simulations show that heat flux density and pulse duration control both the degree of melting in the metal binder and volume heating in the base. With optimized parameters, a single high-energy pulse can reduce porosity and increase bonding strength without melting carbide inclusions.

Effective properties of TBCs may be quantified thanks to different measurement techniques. Image-based analysis represents an alternative method for predicting these effective properties. During the last 10 years, 2D modelling was intensively applied to estimate the thermal conductivity from coating cross-sectional images. However, real coatings present a complex 3D architecture so that the use of 2D computations based on cross-sections has to be validated. In the recent decade, 3D imaging approaches were applied for capturing 3D images of thermal spray coatings with relatively high resolution (up to 1 micrometer). Nevertheless, high resolution brings very large computational systems for which finite-element (FE) methods seem to be unsuitable due to high requirements in terms of computer memory (RAM) capacity. In the present study, a three-dimensional finite-difference-based heat transfer model was developed for analyzing the heat transfer mechanisms through a porous structure by saving RAM usage. An artificial 3D coating image, containing 300×300×300 voxels, was generated from microstructural information measured for a real coating cross-sectional image. In particular, this 3D artificial pore network was generated so that calculations performed on its cross-sections present similar results in comparison with those concerning SEM images of real coating cross-sections. Then, the results computed for the 3D image were compared with those obtained from 2D computations performed on cross-sections of the same 3D image, revealing the differences between 2D and 3D image-based analyses. Finally, the results were then compared with those computed by FE packages (OOF2 and ANSYS).

It has been well known that the coating quality of plasma spraying is strongly influenced by instability of jets in plasma spray due to the arc root fluctuation. A three dimensional (3D) unsteady modeling was employed in the research to analyze the arc root fluctuation in a DC non-transferred plasma torch. Numerical calculations on the distribution of gas temperature and velocity in plasma torch were carried out using argon as plasma gas. The electrical current density and potential were also discussed. The results indicate that the fluctuation of arc inside the plasma torch is mainly induced by the movement of the arc root on the anode surface. The arc root moves downstream with the flow of gas, and the arc will warp from the electromagnetic force simultaneous to the movement. While the arc warps close to the anode boundary, a new arc root is formed somewhere upstream of the original attachment. This article represents nature of fluctuation of arc root, also in this paper we will present that the voltage-drop calculated is larger than that measured experimentally based on the hypothesis of local thermodynamic equilibrium.

Off-line programming technology is frequently used in advanced robot assisted thermal spraying process, such as ABB RobotStudio, which offers excellent functions to simulate the real working environment of robot in order to test the robot trajectory. It also provides the add-in programs to make the simulation easier. ANSYS is an engineering simulation software which offers the function of modeling analysis with grids. The mesh on the surface of workpiece represents a layer with good coverage that can be the reference to create robot trajectory on it. This study provides a new ideal to combine those two technologies (or software) in order to realize the auto-generation of the robot trajectory for thermal spraying. Based on the function of the add-in program, we can transfer the data between RobotStudio and ANSYS using C# programming and then create the trajectory according to the operation parameters. Some experiments have shown that this method can effectively reduce the time required for robot programming.

The development of new plasma spray torches reinforced the use of numerical modelling to help in the design steps. Most of the thermal spray material providers are thus now interested in understanding the arc behaviour inside the torch so that CFD studies focussed on this topic become numerous. Our first calculations performed on the ProPlasma HP gun assuming a laminar hypothesis have shown underestimations of the torch voltage and of the thermal losses in the cooling circuit, and a subsequent overestimation of the thermal efficiency of the torch. In the present study, the setup of different turbulence models was performed and a comparison was made between the results obtained using either the laminar assumption or several turbulence models. The calculations indicate that the results obtained using conventional turbulence models such as k-ε or k-ω type models do not significantly differ from those obtained using a laminar assumption, thus only more sophisticated models can be expected to improve the simulations.

This paper describes computational fluid dynamics (CFD) simulations for state-of-the-art flame-spray processes and experimental validation of these simulations. Alternative nozzle designs are presented along with analysis of their impact on flow-field and flame parameters. Validated CFD models are used for performance prediction of these nozzles. Several variants are compared and the possibility of improvement of technology parameters is analyzed.

In our previous publications the preference was given to develop the theoretical fundamentals which could be used for rapid and sufficiently accurate prediction of thickness and diameter of splat vrs the key physical parameters (KPPs), i.e. temperature, velocity and size of droplet, and substrate temperature. Theoretical solutions derived have permitted to obtain the number of practically useful consequences are of interest for thermal spray technology in context of sensitivity analysis and establishing the inverse link between the splat characteristics and KPPs. For constructive solution of the feedback problem, there are formulated the essence of this notion. The natural basis is the requirements imposed on splats as elements of the mesostructure, from which the coating is formed in the course of spraying. This approach, realized as subsystem “SPLAT”, allows one at the first stage of designing a coating to concentrate the attention on the space-time characteristics of splat formation. After comprehensive evaluation of the operation room of KPPs, providing the formation of splats required, subsystem “SPRAY DEPOSIT” allows one at the second stage of designing a coating to predict its lamellar structure and functional characteristics (porosity, adhesion, cohesion etc.) taking into account a variable surface topology at splat by splat deposition.

During solidification, the cooling behaviour of materials depends on the heat flow through the mould and the alloy composition. Even though the alloy composition is same; the cooling rate can change the properties of the materials. In the present study, an attempt has been taken to predict the cooling behaviour of gray cast iron into a resin bonded sand mould at various thicknesses using JL FEM analyser software. Using K-type thermocouple, the temperature was measured after every 20 sec. Both, the computer simulated and experimentally investigated cooling curves show the similar nature or pattern of the curves. The microstructure also confirms that the cooling rate changes the structure of the cast iron from gray to white.

In the last few years, a new method for surface preparation has evolved, namely thermo-abrasive blasting. This technique utilises a high enthalpy thermal jet to propel abrasive particles. The thermo-abrasive blasting gun, also called a thermal gun, is based on the principles of High Velocity Air Fuel (HVAF) processes. Some empirical data is available on thermo-abrasive blasting method and systems. To effectively improve on nozzle design and productivity, modelling of the thermo-abrasive blasting process was required. This paper describes the computational modelling of the thermal gun with computational fluid dynamic software, namely STAR-CD. The developed computational model can be applied to HVAF systems used for thermo-abrasive blasting and thermal spraying.

A numerical study has been conducted on yttria stabilized zirconia and molybdenum splat cooling taking into account the effects of various parameters. In particular, the effect of the splat thickness, the splat/substrate interface thermal resistance, the latent heat of solidification and the substrate initial temperature on the solidification occurrence and kinetics have been studied. A two-dimension model of heat transfer taking into account the phase change during rapid solidification with an enthalpy formulation has been used for these calculations.

Advances in the functional properties of thermal barrier coating (TBC) deposits are important for increasing the efficiency of, and reducing emissions from both stationary and aircraft turbine engines. Computer modeling is the preferred method for developing new materials with minimum cost and development time. However, modeling of TBCs is complex and must take into account interactions among the layers and with the substrate, in-service phase changes, oxidation, and stress development. Understanding the microstructure of the ceramic layer is important for building these models, as it strongly influences the properties responsible for the basic TBC function – thermal resistance. As is well known the ceramic microstructure changes in service, potentially leading to coating and engine failure. A major challenge is ensuring that the model reliably describes the actual material. Thus, it is important to develop representative models, which can be related to real practical coating systems. We present such a model. It has been developed to interpret small-angle X-ray scattering data that characterize TBC ceramic deposit microstructures. This model is also suitable for incorporation into computer algorithms such as are used in finite-element analysis. Quantitative parameters that describe the microstructure changes occurring under service conditions are readily obtainable for current systems, and these can then be re-measured for future materials of interest.

The combustion assisted thermal spray systems are being used to apply coatings to prevent surface degradation. They offer a highly attractive way to modify the surface properties of the substrate to extend the product life. The quality of combustion assisted thermal spray coating depends greatly on the flow behavior of reacting gases and particle dynamics. The present study investigates the effect of gas phase and its interaction with particles through the nozzle of a thermal spray gun by developing a comprehensive mathematical model. The objective is to develop a predictive understanding of various design parameters of combustion assisted thermal spray systems. The model was developed by considering the conservation of mass, momentum and energy of reacting gases. The particle dynamics was decoupled from the gas phase dynamics since the particle loading in the spray process is very low. The developed model was employed to investigate the influence of various design parameters on the coating quality of thermal spray process.

Plasma coating performances and lifetimes may be ruined during service conditions because of uncontrolled residual stress development within the coating. This study presents the results of a CAST3M thermomechanical numerical model which purpose is to simulate the different residual stresses development within the duplex coating-substrate during the coating built up and its comparison with the experimental results. To achieve the thermal spray process understanding all the thermal fluxes transferred to a metallic beam and surrounding temperatures were measured so as to provide the CAST3M model with precise boundary conditions, corresponding to a specific geometry. The residual stresses were experimentally determined by the in situ curvature measurement and, afterwards, by the hole drilling method. The plasma torch stand-off distance, the relative torch/substrate velocity and the substrate material were considered as the parameters of this study. The main results concern the substrate temperature and deflection during the preheating stage, the thermal energy transferred by the molten splats to the substrate together with the quenching stress and the development of thermal stress during the final cooling.

The mathematical model intended for modeling of the acceleration, heating, and melting of alloyed cast iron particles into plasma jet is presented. Comparison of mathematical modelling and experimental measurement results showed fairly good agreement.

The cold spray process is a relatively new process using high velocity metallic particles for surface modifications. Metallic powder particles which are injected into a converging-diverging nozzle are accelerated to supersonic velocities. In this study two-dimensional temperature and velocity distributions of gas along the nozzle axis are calculated and the effects of gas pressure and temperatures on particle velocities and temperatures inside and outside of the nozzle are also investigated. It is found that the acceleration of the gas velocity takes place in the area of the nozzle throat and it increases and reaches maximum value at the nozzle exit. Due to compression shocks in the area after the nozzle, the gas jet properties show irregular shape and these result in the existence of the maximum particle velocity by the change of particle size at a given gas pressure and temperature.