Coatings produced by thermal spray processes are determined by particle parameters, which can be investigated using various diagnostic systems. In the first part of the paper the different PSI (Particle Shape Imaging) setup are described. Thereby a summary of former publications, presentation of measurements on different thermal spray processes and suggestions of data error evaluations with special difficulties at the particle investigation are shown. In the second part of the paper the new developed mobile experimental setup of PSI is focused. Four important particle parameters (velocity, size, shape and position) can be measured and evaluated. In this part the results and test of new different illumination sources, optical configurations and trigger units are discussed. Furthermore interesting ideas of picture processing and data evaluation are depicted and explained in more detail. First comparison of the results measured with DPV2000, SprayWatch and additional Voltage-Current-High-Speed- Camera investigations are shown. The complete paper concludes with an outlook for future combination of further established diagnostic systems (i.e. find the optimal distance between substrate and thermal spray system).

Failure is an inevitable consequence with thermal barrier coatings and failure modes are complicated due to irregular microstructure in the coating layers and wide range of external conditions. In this study, three-point bend tests are used to monitor damage evolution in YSZ-CoNiCrAlY TBCs on superalloy and stainless steel substrates. Coating samples, consisting of the bond coat and topcoat, were deposited by atmospheric plasma spraying on test specimens measuring 80 x 6 x 4 mm. The long, narrow specimens were subjected to three-point bend testing, using acoustic emission sensors to detect the formation and propagation of cracks in the coatings and plastic deformation in the substrates. The investigation results indicate that variations in acoustic emission signals correspond well with changes observed in the stress-strain curves of the coatings and substrates and that failure mechanisms can be systematically analyzed based on the amplitude, frequency, and energy of the acoustic emission signals. A detailed description of the actual failure process is provided.

This study demonstrates an experimental setup in which acoustic emission sensing is used to monitor a twin wire arc spraying (TWAS) process. Emitted acoustic signals were recorded by broadband sensors attached to the spray nozzle and mounted under the substrate. Sensor outputs were converted from the time domain to the frequency domain by fast Fourier analysis. Acoustic emission amplitude plots were produced and are correlated with gas pressure, arc voltage, in-flight particle velocity and temperature, coating thickness, and crack formation due to cooling.

The image-based measurement method 2D Continuous Particle Image Velocimetry (2D Continuous PIV) is commonly used for measuring particle velocities in thermal spraying processes due to its basic measurement setup and its large measurement volume compared to methods based on point sensors. The accuracy of such image-based measurement techniques depends on the measurement algorithm, the process environment, such as distributions of particle characteristics, and the error of the imaging system. However, in the case of 2D measuring, accuracy might also depend on the fact that 2D methods measure only two of the three velocity vector components while ignoring the third component. In this paper, the impact of measuring only two of the three velocity vector components on the accuracy of a closed-source 2D Continuous PIV algorithm is investigated. The analysis is based on a virtual measuring instrument that includes optical aberrations of the imaging system and it is shown that this error contribution of measuring only in 2D is within acceptable limits for typical thermal spraying processes.

Thermal spray coating applications require precise control of substrate temperature during deposition in order to achieve optimum performance of the final part. Applications such as high-velocity oxy-fuel (HVOF) hardfacing of aircraft landing gear and plasma spraying of thick sputtering targets are but a few examples where control of substrate temperature throughout the entire coating cycle is critical. A broad effort to develop a versatile and cost-effective cryogenic gas cooling system for controlling part temperature in high-energy thermal spray operations is described. Results show that the new liquid nitrogen cooling technology can significantly improve productivity of many conventional operations and provide corresponding powder and process gas savings by completely eliminating the need for interpass cooling breaks. Optimized temperature control and minimization of coating oxidation during the spraying process, resulting from the use of the new system, were also found to: (1) preserve substrate properties, (2) decrease residual stress gradients at coating interfaces, (3) enable applications of soft masking materials, and (4) increase the deposition efficiency (DE) of WC-CoCr coatings while minimizing decarburization of the WC phase. This work focused on HVOF spraying of WC-CoCr coatings which offer a performance and cost alternative to toxic chromium (Cr 6+ ) plating but yet to be published, recent experimentation with the other coating materials and deposition systems was consistent with the observations reported here.

A substrate surface thermocouple was developed for thermal spraying. The substrate used for the study is a porous 430 stainless steel disk, though the thermocouple concept can be applied with other materials. Type N thermocouple wires are cemented in holes through the substrate, and then a copper coating is deposited across the surface to electrically connect the wire tips to complete the thermocouple circuit. The copper also promotes temperature equalization between the wire tips and the surrounding substrate surface to increase accuracy. Using finite element analysis (FEA), it was determined that the optimum thickness of the copper layer is 38 µm. With this thickness, the thermocouple should be able to measure peak-to-peak surface temperature swings due to a passing plasma jet within +/-3% when the copper thickness is uniform and all physical properties of the coating and substrate system are well-known. However, a number of assumptions were used for the FEA, so a detailed uncertainty analysis was performed. This analysis found that the expected accuracy window of the thermocouple is +19%/-10% as implemented for measuring surface temperature swings. For measuring average temperatures, the thermocouple is very accurate, because large heat fluxes into the substrate occur only when the plasma torch is directly in front of the substrate. Experimental measurements of surface temperatures with the optimized thermocouple are presented.

The influence of spray parameters on particle with the improved plasma gun was studied by using SpryWatch-2i System. The results show that the particle velocity increases and exceeds the velocity of sound when using a new designed nozzle (C2 nozzle) during the plasma spraying. Under a certain condition, the particle velocity varies as the spray distance rise firstly, decline then, as the primary gas pressure increases, the particle velocity increases, the particle temperature drops firstly then increase, the velocity increase a little. But as the steadily increase of the flow rate, the influence on the particle temperature drops, the influence of arc voltage on particle velocity and temperature is slightly. Arc current influent little on particle temperature, but the particle velocity increase in a range.

Impact of liquid injection on atmospheric plasma has been measured by an enthalpy probe and visualized by shadowgraphy. Liquid was injected by two nozzles. A solid stream nozzle with 0.3 mm diameter and an atomizing nozzle with a spray angle of 30°. For constant liquid flow rate and varied plasma current an optimal injection parameter has been obtained. Influence of different flow rates on plasma characteristics has been examined. Full profiles along each axis show differences for different injection techniques in enthalpy, temperature, velocity and composition.

The Oxy-Fuel Ionization system (OFI) is a new thermal spray process which consists basically on a high velocity combustion process enhanced by a low energy plasma source. The system is characterized by its stability over a relatively large range of fuel/oxidant conditions, the possibility to use poor fuels like natural one (with low gas consumption) and the high deposition rates that can be achieved in comparison to conventional HVOF guns. The OFI gun has been designed following a modular concept, which in combination with the high flexibility of the system is expected to allow the deposition of coating materials with the most different physical and chemical natures. This work deals with the experimental analysis of the process using methane as fuel gas and its correlation with the deposition of WC-base materials. Two in-flight particle diagnostic systems were used: the Spray Watch diagnostic system (from OSEIR) and the Spray and Deposit Control (SDC) system (developed by the SPCTS laboratory of the University of Limoges). Results are presented for the most representative properties of the optimized coatings (micro hardness distributions on the coating cross section and crystallographic analysis).