Thermal spray (TS) technology has attracted the attention of numerous industrial sectors due to its apparent simplicity and versatility. It has been used across the world for over 80 years in the conservation and creation of art. Despite the creativity involved in the creation of an art piece, the TS artistic endeavors are limited and insufficiently explored. Unique material combinations, usually not observed in conventional engineering applications, can be achieved with TS technology. Although the material amalgamation possibilities are infinite, their combined deposited characteristics, interfacial compatibility and color palette require further study. In this work, the fields of photography, image processing and TS are combined to produce a large art-piece using the cold gas dynamic spray (CGDS) process. Aluminum, zinc, nickel, alumina, steel and titanium alloy powders are sprayed to replicate in three-dimensions a photograph of a crinoid from the Silurian period found on the Anticosti Island, located in the Gulf of St. Lawrence in Canada. The numerous steps required to produce the artistic 3D piece, namely numerical segmentation of the photograph, conversion to a computer-assisted design (CAD), manufacturing of steel masks and CGDS deposition of the selected powders to reach the sought color palette are described. Powder deposition efficiency, material compatibility and microstructural characteristics are analyzed. and the resulting art piece is presented.

The Fraunhofer Institute for Material and Beam Technology IWS in Dresden has developed “Lightblast,” a laser ablation technology for creating clean, structured surfaces. Lasers offer precision, reproducibility, cost-effectiveness, and environmental friendliness, opening new possibilities in surface treatment. Traditional blasting processes employ compressed air to propel abrasive particles at high speed onto a substrate. This method often results in embedded abrasive particles, surface contamination, and rapid abrasive wear, compromising process consistency. Additionally, the abrasive waste poses environmental and disposal challenges. Lightblast utilizes a continuous wave single-mode laser and a dynamic galvanometer scanner to precisely vaporize the substrate without abrasives. Adjustable parameters control the resulting surface roughness with high reproducibility. Unlike pulsed laser ablation, the continuous wave laser enables higher productivity due to increased power. Furthermore, Lightblast allows for selective surface structuring based on CAD designs without additional masking. Target applications include surface preparation for coating, bonding, and joining processes.

The use of cold spray in metal additive manufacturing (AM) offers well recognized advantages with typical commercial drivers being a rapid build rate, low process temperature, and wide range of usable alloys. Cold spray AM to date has often employed a methodology of rapid material deposition, with or without masking, into relatively simple shapes and wide tolerances that can lead to constraints in part geometries and/or significant post-spray machining. In this work, an investigation has been performed into producing more complex geometries and improving shape fidelity using a conventional AM strategy; namely, starting with a CAD drawing, slicing the CAD geometry into a layered structure, and performing a layer-by-layer build. For cold spray, technology-specific considerations must be factored into each of these steps and in particular, an effective build strategy and toolpath are critical to moving towards near-net shape parts. This requires, by extension, precise manipulation of the spray gun, or part as applicable, which was performed using industrial robot offline programming via commercially available software. Various cold spray 3d builds are used to demonstrate developments in toolpath planning and build strategy.

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.

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.

We used a three-dimensional model of droplet impact and solidification to simulate the effect of surface roughness on the impact dynamics and the splat shape of an alumina droplet impinging onto a substrate. The substrate surface was patterned by a regular array of cubes spaced at an interval twice their size. Three different cube sizes were considered, and the results were compared to the case of droplet impact onto a smooth substrate. To understand the effect of solidification on the droplet impact dynamics and splat morphology, the simulations were run with and without considering solidification. Comparing the results, we have concluded that solidification plays a major role in determining splat shape on a rough surface. We also present results of the distribution of voids between the splat and the substrate.

The economic efficiency of spraying a frequently changing spectrum of parts is strongly dependent on the costs of planning the spray process. In many cases, the robot program for coating a three-dimensional surface is generated directly on the control unit computer. Programming results in costly downtime. At IWS, a technology for off-line programming of robots and CNC systems for thermal spraying (TS) and laser cladding (LC) was developed. Coating programs are developed using CAD data from a workpiece and checked with simulation software. All steps are accomplished off-line without influencing ongoing production. Off-line programming of spray processes for three-dimensional surfaces enables substantial time savings to be realized, more so with increasing part complexity. These programs enable a constant spray distance and traverse speed as well as a permanent spray angle of 90° to the substrate to be achieved.

This work deals with a 3-D transient simulation of the air plasma spraying of ceramic powders using a C.F.D. commercial code ESTET v3.4 that has been adapted to thermal plasma conditions. The mathematical model computes the distribution of particle velocity, temperature, molten state and size at impact and predicts the heat transfer to the substrate by plasma jet and particles. It incorporates the conversion from electrical to thermal energy in the torch nozzle as well as coating formation on the substrate. It makes it possible to predict the shape of the coating footprint when the torch and the substrate are fixed. The projections of the model are compared with experimental results that involve flow characteristics, time-dependant particle behavior in the flow and heat flux to the substrate.

We used an object oriented finite element numerical method to examine residual stress build-up in a simulated crosssection of coating. The cross-section image of coating was the result of simulation produced by a 3-D stochastic model of thermal spray coatings, which model features of coating microstructure including internal pores and surface roughness. An adaptive meshing technique was used to fit a grid in a section through the simulated coating, and stresses in the coating calculated using a finite element method. The results showed that stresses are sensitive to the thickness and roughness of the coating.

The objective of this study is to increase the deposition rate in the plasma-spray manufacturing of thermal barrier coatings without altering the quality of the coatings. The experimental part involves the measurement of in-flight particle characteristics and analysis of coatings properties when varying the hydrogen content of the plasma-forming gas, the torch nozzle diameter and the powder feed rate. The experimental results of particle measurements are discussed in the light of the gas flow fields projected by a 3-D model of the plasma spray process.

The paper presents the basic principle and application of High Velocity Arc Spraying technique. Through adopting convergent-divergent nozzle, air circulation cooling and computer aided design technique, particle velocity was enhanced, which surpasses velocity of sound, and atomization effect was improved, so HVAS fabricated high quality coating. Experiment results show that HVAS has high particle velocity, high atomization effect, high bond strength and low porosity. Average velocity of atomized Aluminum particle is 373m/s. Bond strength, porosity and average particle size of 3Cr13 coating are 60MPa, 0.9% and 4.32 m respectively. For high coating quality, HVAS is widely used in maintenance, corrosion resistance and surface strengthening.

The effect of substrate characteristics on the formation of plasma-sprayed alumina splats was studied using both experiments and numerical simulation. Knowledge of the particle and substrate conditions is critical in understanding coating formation and in validating computational models. The size, velocity and temperature of the alumina particles prior to impact were measured using a particle in-flight diagnostic system. Experiments were performed on two substrate materials: stainless steel and glass. Substrate temperatures were varied in a range of 20-500°C and controlled with an electric heater. For each substrate material, a transition temperature was observed above which there was no fingering/splashing and the splats had a circular disk shape. A 3D computational model of free surface flows with heat transfer and solidification was used to simulate the impact of alumina particles in conditions given by the experiments. The splat shapes from numerical model were comparable to those of the experiments for hot stainless steel substrate. For a cold substrate, the numerical model did not show any fingering/splashing. In the experiments, however, we observed two types of splat shapes: intensive splashing with no central core and circular disk splat. Substrate surface contamination, not considered in the numerical model, was the probable cause of droplet splashing on the cold substrate.

In view of its advantages (simplicity, low cost, high deposition rate), the wire arc spray process has become a widely used technology for the spraying of metals. Nevertheless, numerous parameters (gun design, atomizing gas nature, velocities, pressures, ...) may have a significant influence on the quality of the produced coatings. One of the major problems related in the literature concerns the poor control over the spray pattern; the understanding of this phenomenon has thus become essential for further improvements. In the present study, a special feature of the PHOENICS commercial code (from CAD to CFD ) was used to produce a 3D simulation of the flow within the gun and outside. This method was especially useful in view of the complex geometry of the TAFA 9000 gun, which was investigated. The results show the presence of a highly asymmetric external jet.

This paper presents a numerical simulation of the plasma spraying of alumina particles using a three-dimensional commercial fluid dynamics code ESTET 3.4 . The objective of this study is to investigate the effect of (i) turbulence model and turbulence radial profiles at the torch exit on plasma flow and particle behavior, (ii) particle injection conditions on particle trajectories and heating and (iii) plasma jet fluctuations on temperature and velocity flow fields. The comparison of predictions with experimental measurements of gas and particle velocity and temperature, makes it possible to determine the influential parameters and set them to pertinent values.

A three dimensional model of coating formation has been developed. Using the model we are able to simulate coating formation by deposition of large numbers of droplets. The properties of impacting particles are assumed to vary stochastically using a normal probability density function. Splat curl up is assumed to be the source of porosity formation. The model is able to predict coating porosity, thickness and roughness as a function of spray parameters.

Features and computation power available in CAD systems allow modeling of manufacturing processes to a certain extent. This paper deals with the simulation and optimization of the final coating by plasma spraying. Experimental confirmation of the model is described in and simulation results are presented. Although a number of questions regarding the formation of the coating remain in some critical cases, the results show that simple models provide a sufficient approximation of the simulated plot for off-line robot programming. Paper includes a German-language abstract.

Various models exist of the 2D impact of a molten thermal spray particle onto a flat solid surface. Such models, however, cannot be used to examine 3D effects such as the asymmetric splashing and breakup which are common under thermal spray conditions. The focus of the present work is on such effects. A 3D model of droplet impact has been developed which predicts splashing and the subsequent formation of small satellite droplets. The model is a 3D version of RIPPLE (LA12007- MS), an Eulerian fixed-grid finite volume code utilizing a volume tracking algorithm to track the droplet free surface. Simulations are presented of the impact and splashing of a molten tin droplet, and the results compared with photographs. A simple model, based on Rayleigh-Taylor instability theory, yields an estimate of the number of satellite droplets which form during impact. Finally, a simulation of droplet impact under thermal spray conditions demonstrates breakup, although in the form of a corona which separates from the bulk of the fluid.