This work provides a new in-situ measurement method for the analysis of the spray-spot geometry and the thermal properties of the coating. The new approach is based on infrared detection of the thermal radiation from the coating surface combined with a subsequent automated spray-spot characterization. With this method it is possible to describe the geometry, the axis-position of the torch, the powder injection properties, and the temperature distribution in of the spray-spot. Especially for the automated production in high quantity the spray-spot analysis is a useful assistance for the operator because the detector reacts very sensitive on small changes of the process conditions. With regard on important fields of application (e.g., gas turbine production) the sensor is suitable to detect drifting spray system parameters. Also, the progression of wear at the nozzle, injector and electrode can easily be estimated. In recent research the in-situ spray spot analysis is being developed further for the characterization of multipair electrode plasma generators.

Boundary layers on surfaces will change from laminar to turbulent flow after a critical length. Due to the differing heat transfer coefficients of laminar and turbulent flow, the point of transition can be detected by heating the surface and measuring surface temperature by thermographic imaging. Locating the transition point is crucial for the aerodynamic optimization of components. In this study, fiber reinforced polymer composites (FRPCs) were chosen as the test substrate. Experiments were conducted using the flame spray process and NiCrAlY coatings. Multilayered coatings consisting of an aluminum bond coat, a layer of alumina as electrical insulation, and a heating layer of titania were fabricated by atmospheric plasma spraying. Free-flight tests were conducted with a functionalized winglet in order to assess the ability of thermally-sprayed heating elements to detect the location of transition of the flow regime. The results showed that the thermally-sprayed elements heat surfaces uniformly, with sufficient radiation losses for thermographic imaging. It was also shown that the change in temperature at the point of transition was readily observable using thermography.

The alloys CuAl9Ni5Fe4Mn and CuMn13Al8Fe3Ni2 were arc-sprayed with a spiral-shaped pattern in this work, using both pressurized air and a mixture of nitrogen and hydrogen. Process temperatures were recorded by thermographic imaging and residual stresses were measured by modified hole-drilling method. Moreover, analyses of the cavitation erosion behavior and other properties were carried out. It was found that a change in the spray pattern can strongly reduce residual stresses and material loss by cavitation erosion.

The aim of this study is to determine how various factors, including process parameters and nozzle configurations, affect the shape and size of the spray jet in twin wire arc spraying. In the experiments, steel specimens were sprayed using an iron-based cored wire with a fused tungsten carbide filling. In-flight particle temperature and velocity and fluctuations in voltage and current were measured during spraying. The shape of the thermal spray spot and the 3D footprint of the plume were determined by means of image analysis and tactile surface profiling methods. The results obtained show that spray plume characteristics, and thus particle distribution, are heavily influenced by secondary gas flow, particularly the number, location, and angle of atomization outlet holes in the secondary gas nozzle.

Time-resolved thermographic measurements were performed by a high speed infrared camera on a substrate surface during cold gas dynamic spraying without powder particles. Experiments were carried out on three commercial cold spray systems (Centerline SST, CGT Kinetiks 3000 and Inovati KM-CDS 2.2) spanning a wide range of gas pressures, gas temperatures, gun traverse speeds and stand-off distances. The substrate surface temperatures were measured directly beneath the cold spray gun nozzle as well as at predetermined distances from the gun giving a general evaluation of the heat input to the substrate in actual deposition conditions. It is shown that the substrate surface temperature can rise to a value close to the inlet gas stagnation temperature in the area located beneath the cold spray gun (bow shock region). For the same set of process conditions, significant differences were found in measured surface temperature range between the three cold spray systems, due to differences in nozzle configuration.

One major shortcoming of thermal barrier coatings applied to gas turbine components is the spallation of the ceramic coating under mechanical stress developing during thermal cycling environments. In order to study the evolution of failure and the expectancy of lifetime under realistic conditions cycling burner rig tests are a well established matter of choice. In the same way the techniques of acoustic emission (AE) testing and infrared (IR) thermography have been widely proofed to provide insight to microscopic crack formation and localization of hidden delaminations, respectively. Both techniques can be utilized to record the evolution of microscopic and macroscopic defects in advance to the apparent failure. Indirectly, this knowledge allows to verify and to improve lifetime models. The aim of this study is to expand the use of AE and IR testing as a rugged in-situ monitoring tools for combustion driven cycling rigs and to provide spatial resolved information on thermal load and failure evolution of the TBC in those tests. For a successful application to an experiment using a gas fired and air cooled burner rig some it is necessary to overcome some limitations which are mainly due to the high level of interfering signals under those experimental conditions.

This paper presents selected research results of the DFG founded project group, consisting of four institutes focusing on diagnostic methods in thermal coating processes. The aim of this group is to characterize the Atmospheric Plasma Spraying (APS) process by means of diagnostic methods so that – based on the requirement profile of the coating – appropriate adjusting of the process parameters can be realized. For this purpose, different diagnostic tools like Particle Shape Imaging, Laser Doppler Anemometry, Schlieren Technique, Particle Image Velocimetry, Enthalpy Probe, DPV 2000 and Thermography were qualified and adjusted to each other. Most of the results presented in this article are limited to the area close to the substrate which is difficult to handle with diagnostic methods. Additionally, new achievements concerning nozzle design and system enhancements are introduced.

The aim of the project group consisting of four research centers and founded by the DFG (German Research Society) is to characterize the plasma spraying process by means of diagnostic methods so that, based on the requirement profile of the coating, appropriate adjusting of the process parameters can be realized. For this purpose, different, partly newly-developed diagnostic tools, like Particle Shape Imaging, Laser Doppler Anemometry, Streak Technique, Particle Image Velocimetry, Enthalpy Probe, DPV 2000 and Thermography were qualified and adjusted to each other. The new results presented in this article are limited to the areas of particle injection and substrate which are difficult to handle with diagnostic methods.

This paper describes the equipment and procedures used to investigate the effects of the heat load on SOFC surfaces during vacuum plasma spraying. It explains how the authors used a vacuum-sealed IR camera to record thermographic images of the substrate surface as they sprayed different powders and as they varied the dc power, scanning speed, and stand-off distance of the plasma torch. The authors also studied the effect of different cooling methods, including conductive cooling from the backside via a water-cooled aluminum backplate and convective cooling from the front side with a nitrogen gas jet. Using the experimentally obtained data, the authors developed a thermal 3D model of the SOFC plasma spraying process that accounts for torch movements, substrate cooling, and layer growth. An outlook for future work is given expressing an intent to model stress fields within fuel cells during plasma spraying in order to simulate the development of residual stresses. Paper includes a German-language abstract.

This paper discusses the use of IR thermography in the development and control of thermal spraying processes. In the experiments, Al 2 O 3 layers are plasma sprayed on steel, aluminum, and glass substrates while recording surface temperatures. The measurements are then used to establish a correlation between temperature control and internal stress in the layer composite. The work shows that substrate preheating and torch kinematics have a significant effect on residual stress. Paper includes a German-language abstract.

This study examines the influence of in-flight particle properties and substrate temperature on the quality of ceramic layers obtained at atmospheric plasma sprayings. Investigators sprayed aluminum oxide and zirconium dioxide powders on metal substrates, using infrared temperature measurement techniques to monitor the process. The authors present the test data and explain what it reveals about particle flattening behavior, coating morphology, and the effect of cooling. The investigations show that the influence of substrate temperature must not be overlooked if layer properties are to be predicted and controlled. Paper includes a German-language abstract.

Many thermal spray coating applications require an optimum performance regarding the thermal and mechanical stability of the layer composite. The maximum loads that a composite can sustain, are not only dependent on the intrinsic material properties of the coating, but are also subject to the quality of deposition. The quality of the coating is predominantly influenced by the temperature distribution during the deposition process thereby influencing the residual stress development. Therefore failure of a thermally sprayed coating under mechanical and/or thermal load often could be avoided by an adequate deposition process with well controlled heat and mass transfer, i. e. by avoiding hot-spots on the surface that result in high residual stresses in the composite. With the help of Infrared (IR) thermography an imaging of the lateral and spatial temperature field of a workpiece surface and its evolution in time can be monitored and visualised. In the presented work the atmospheric plasma spraying process serves as an example to demonstrate the suitability of thermographic imaging as a quality control and process optimisation technique for online process monitoring and control in thermal spraying. The results indicate that IR-thermography can be used as a flexible tool for on-line process control of coating manufacturing via thermal spraying, it offers a powerful way to optimise the deposition process.

The control of the coating quality becomes more and more important. Infrared methods are well introduced in industry for several types of inspections. The lock-in thermography is based on modulated heat flux and is proved for composite materials and electronic components. In combination with an IR-camera seems to meet the requirements of a modem quality control system. The off-line measurement takes about 3 up to 5 minutes depending on the geometry of the surface. The paper gives an overview on the principle, the technical details of the measurement and the correlation of the detected signals and the coating properties will be discussed. The accuracy concerning the thickness is determined for different coatings (e.g. WC-Co).

An industrial and cost-effective online quality control method for thermally sprayed coatings will be presented. A new concept in pulse-thermography allows online, during the spraying process, the non-destructive evaluation of coated surfaces. This technique employs a heat source that produces a heat impulse. The impulse is directed toward the examined surface and the from the surface reflected and/or emitted signal is collected by an infrared-camera and subsequently treated in a computer. It will be demonstrated that the spraying process itself can be used as a heat source. In principle, the fading behavior of the signal captured by a high speed infrared camera is observed, or else the progression of the induced heat wave within the coating. Differences in coating thickness, coating and adhesion defects, microstructural changes, an aggregation of pores as well as oxide or metallic inclusions provoke a significant change in the signal intensity and are therefore detected. Pulse-thermography enables the non-destructive assessment of the quality of thermally sprayed coatings. A coated part can be examined to check if the desired coating structure has been successfully attained or if and where there are any areas with critical deviations in respect to coating thickness or coating microstructure. The simple set-up allows the integration of the technique in the production line.

Lock-in thermography is a nondestructive inspection method based on modulated heat transport in combination with infrared imaging. Measurement times are relatively short, about 3 or 4 minutes, and the method is amenable to inspecting a wide range of large and small parts. This paper describes the basic principle behind the method and its application to different thermal sprayed coatings (e.g., Cr-steel, Al2O3). It explains how the test samples were prepared with artificial defects simulating delaminations, inclusions, and other types of imperfections and how the method performed in each case.

Thermal spraying is a widespread coating process with various applications in many industry branches. To be able to spray successfully on the sensitive materials an in-situ temperature control is most beneficial. The objective of this paper is to find out the correlation between the mechanical properties of some coating-substrate variations and temperature history of the coating made by HVOF. The paper describes the processes involved in implementation of the thermographic measurement systems into the HVOF spray system to measure the temperature of the coating on aluminum and steel during spraying. It was observed that when spraying on aluminum, the temperature of the coating has a marked influence on the adhesion. Tests with a steel substrate show how the hardness of the WC-CoCr depends on the quenching speed of the coating during spraying. Paper includes a German-language abstract.