Abstract This paper is describing a new tool, based on optical emission spectroscopy, for the detection and the recording of short and long term variations in thermal spraying applications. By using an online analysis of the emitted process spectra the user is enabled to get direct access to the running process and the resulting coating quality. It has been proved in numerous investigations that all relevant process parameters, which are significant for the layer forming and its properties, can be separated and detected. Furthermore, first investigations are showing that all results obtained for plasma spraying applications can be transferred to wire arc, flame and high velocity oxygen fuel spraying. Paper text in German.

Abstract This paper aims to characterize with innovative methods bond coat and yttria partially stabilized zirconia powder and coating. Bond coat layers realized with different deposition techniques were anlyzed by X-ray Photoelectron Spectroscopy (XPS) in order to compare deposition technologies from the point of view of the oxide presence. X-ray diffraction and Raman microscopy were performed in order to determine the crystallographic composition of Yttria Partially Stabilized Zirconia powders and top coat layers. The surface and interface roughness is expected to affect spallation resistance of the thermally grown aluminum oxide and the life of thermal barrier coating. Raman microscopy allow to map the surface of the examined samples, retrieving the monoclinic zirconia distribution with high spatial resolution. XPS measurements were carried out in order to determine the surface elemental composition. This turns to be useful to measure the amount of oxides which forms during the spraying process and the thermal treatment. Paper includes a German-language abstract.

Abstract The direct-current arc plasma jet generator is a promising plasma device suitable for economically assisting material processing in which a high throughput of material is desired. In this paper, spectroscopic and electrostatic probe measurements are made to examine plasma characteristics near a titanium substrate plate under nitriding for a direct-current arc plasma jet generator with a supersonic expansion nozzle in a low pressure environment. Heat fluxes into the plate from plasma are also evaluated with a Nickel slug and thermocouple arrangement. Ammonia and mixtures of nitrogen and hydrogen are used as the working gas. The relationships between the plasma and heat flux characteristics and the substrate nitriding characteristics are discussed. Paper includes a German-language abstract.

Abstract A stronger integration of thermal spraying in industrial production lines is essentially prevented by insufficient options for process control. Emission spectroscopy is a passive characterization method that requires very short measurement times and is therefore suitable for in-situ applications. For many coating applications, contamination cannot be tolerated. The use of certified spray powder, for example, cannot avoid inclusions of tungsten, which can be traced back to the detachment of droplets from the electrodes of a DC plasma torch. Monitoring the emitted spectrum of a flame during the spraying process enables the detection of process or material-related impurities. In addition, emission spectroscopy offers great potential to be developed into a process control tool that uses the local intensity of characteristic emission lines. In this paper, investigations with different spraying methods are carried out, and the results are evaluated against the background of the process characteristics. Paper includes a German-language abstract.

Abstract A two-wavelength particle imaging pyrometer has been developed to measure temperature, velocity and size of individual particles within a field of view and a depth of field that spans the entire particle stream in most thermal spray devices. The pyrometer provides continuous updates to particle condition profiles, histograms and correlations. The software locates particle streaks, determines the intensity ratio and dimensions of each streak, and calculates the particle temperature, velocity and size. Many forms of advanced materials processing technologies, such as thermal spray, spray-forming and atomization processes, have considerable need of process control sensor technology. These measurements provide the basis for application of the pyrometer to many of these processes. Particle temperature measurements of plasma-sprayed ceramic powder were obtained using a spectrometer and the pyrometer. Comparisons of the measurements show that the vision-based pyrometer has excellent accuracy. The standard deviation of the measurements was 40 K or about 1.3 %. Additional pyrometer measurements were used to determine its minimum detectable temperature and velocity change, which were 12.4 K and 2.77 m/s, or 0.4 % and 1.5 %, respectively. The vision-based particle sensor can now be applied to high performance control strategies to provide stable particle temperatures and velocities over long duration plasma spray processes.

Abstract Air entrainment in the first 30 mm of a dc Ar/ H 2 plasma jet has been studied by emission spectroscopy. The tests were conducted using 6, 7 and 10-mm diameter nozzles and plasma arc currents of 400 and 600 A. Oxygen, nitrogen, and argon spectral lines were recorded 20 and 30 mm downstream of the nozzle exit during spraying, and the corresponding atom density ratios were estimated based on plasma population temperature and volumetric emission coefficients. The results indicate that at 20 mm air entrainment is mainly due to piston flow for the 10-mm nozzle and both piston flow and engulfment for the 7-mm nozzle. At 30 mm, the engulfment process is found to have 4 to 6 times the impact that it does at 20 mm and is directly linked to the jet velocity. At both locations, the atom density ratios differ from that observed in air due to the time required to dissociate N 2 .

Abstract This paper compares two methods for determining the composition of Ti/TiN coatings deposited by reactive plasma spraying. The coatings were obtained by spraying titanium powder in a low-pressure N2/Ar atmosphere. The resulting film has a variable nitrogen content in the form of titanium nitrides, depending on gas partial pressure, total pressure, sample-source distance, and other parameters. The composition of the film was determined using X-ray diffraction and X-ray photoelectron spectroscopy. The two techniques provide similar results and either can be used for the compositional characterization of these coatings.

Abstract The isothermal and cyclic oxidation of freestanding Ni-20Cr-10Al-lY thick coatings has been investigated at 1200°C using TGA, SEM, XRD and XPS techniques. Coatings produced by HVOF are dense and remain crack free after thermal treatments. The protective oxide layer formed did not flake off upon cyclic oxidation as confirmed by SEM analysis. In addition, three oxidation regimes were identified after analyzing TGA data: two below 1000 °C and a third one at approximately 1200°C. The regimes below 1000°C correspond to the selective oxidation of elements on the surface and at the subsurface of the coatings whereas the third regime involves element diffusion from the bulk of the coating to the surface. The oxidation regime became asymptotic at 1200 °C as stable oxides formed. The presence of water vapor affects neither the thickness nor the orientation of oxide crystals formed on the surface as confirmed by the X-ray analysis. The XPS and X-ray results show an inter-diffusion between the coating and substrate with a slight increase in chromium concentration at the interface. Element distribution within the oxide layer was found to follow the order: Al-(oxide)Y-(oxide)/Cr-(oxide)/Ni-(oxide)/NiCrAlY from the outermost oxide layer to the bulk of the coating. These results show that HVOF dense Ni-20Cr-10Al-lY sprayed coatings can be used as anti-oxidant barriers in both isothermal and cyclic oxidation at 1200°C.

Abstract The quasi-steady magneto-plasma-dynamic (MPD) arcjet generator is a promising plasma accelerator, which has a coaxial electrode structure similar to those of conventional plasma torches. The MPD arcjet generator utilizes principally electromagnetic acceleration of the interaction between the discharge current of kiloamperes and the azimuthal magnetic field induced by the discharge current, although the working gas is accelerated aerodynamically through a nozzle in a thermal arcjet generator. In this paper, ablation-type MPD arcjet generators are developed for ceramic coatings. Discharge voltages and ablation rates of ceramic materials are examined, and front velocities of ablated atoms of ceramic component are also estimated using a streak camera. The Vickers hardness of coating is measured. Their cross sections are observed with a scanning electron microscope, and their surfaces are analyzed by means of x-ray diffraction and x-ray photoelectron spectroscopy. Paper includes a German-language abstract.

Abstract Ammonia and a mixture of nitrogen and hydrogen are used for material processing. Since these gases are chemically active, the processing efficiency is enhanced. This article describes a study to understand the physical properties of ammonia and a mixture of nitrogen and hydrogen plasmas inside and outside an arcjet generator. Spectroscopic measurement is made, and several plasma properties are determined from the data. The result shows that the H-atom electronic excitation temperature and the nitrogen rotational excitation temperature decreased from 7000-11000 K in the constrictor to about 4000 K and to 1000-1500 K, respectively, on the nozzle exit with mass flow rates of 0.1-0.2 g/s at input powers of 7-12 kW. However, the NH rotational excitation temperature did not show a significant axial decrease even in the downstream plume. Paper includes a German-language abstract.

Abstract In this paper, the processes associated with the formation of the tungsten carbide phase are studied and determined. A plasma-compressed WC+12%Co powder is sprayed with a CDS-100 gun. WC+Co coatings are obtained by (High Velocity Oxygen Fuel technology. The coatings are characterized using scanning electron microscopy, energy dispersive system, and transmission electron microscopy in order to record and identify the tungsten carbide phase. The mechanisms for the formation of the tungsten carbide phase are discussed. Paper includes a German-language abstract.

Abstract This paper investigates the degradation of polymers during thermal spraying with special reference to the changes in molar mass. A study is carried out on the degradation of polymethylmethacrylate (PMMA) during plasma spraying. The infrared spectroscopy showed that the coating did not lead to any significant chemical reactions. However, the gel permeation chromatography measurement revealed larger changes in the molar mass with a decrease of up to 70% in the average numerical molar mass of the PMMA. The results show that increasing the arc power resulted in a substantial increase in degradation. Because of the extremely low thermal conductivity of polymers, the magnitude of these effects becomes even worse. The results indicate that it is important to consider molar mass measurements along with spectroscopic analysis when characterizing thermally sprayed polymer coatings. Paper includes a German-language abstract.

Abstract Using a DC-plasmajet amorphous and nanocrystalline Si-C-layers are synthesized from chloromethylsilanes on various substrate materials. Though most of the layers show granular morphologies with cluster diameters between 25 and 400 nm depending on the process parameters, coatings with a dense or columnar morphology and with a smooth surface can be synthesized as well. XRD analyses verify β-SiC crystals with an average diameter of 5 nm. In some samples produced from carbon rich precursors also graphite is detected. Depending on the substrate material and the process parameters deposition rates up to 1,300 µm/h are obtained. Apart from silicon and carbon the coatings convey oxygen and chlorine verified by EDX. Coatings removed from the substrate can withstand several bending cycles (45°) without any visible indication of failure. Paper text in German.

Abstract Infrared techniques are well introduced in industry for several types of inspections. For non-destructive testing of thermal sprayed layers they couldn't be applied very successfully due to the limited resolution. Although, new developed and very fast infrared sensors combined with a miniaturised cooling system (like Stirling motors) allowing today the development of a new generation of portable infrared systems for non-destructive and fast testing of sprayed layers on large surfaces. This paper reports on results got with a first prototype of such a new designed infrared camera. It will be demonstrated that it is possible to prove coatings quality on large machine components independent of the material combination. The inspection speed is several times faster than the time used for spraying. Coating thickness measurements as well as defects like cracks or areas of bad bonding can be done with a resolution down several micrometers. Even differences in coatings quality are possible to identify, as for example the level of dilution of carbides of HVOF sprayed WC-Co coatings. Paper text in German.

Abstract This paper investigates the problem of complete evaporation of zirconium oxide powders that are injected into a thermal RF plasma. Particle trajectories and evaporation are studied using optical emission spectroscopy and laser Doppler anemometry. Model calculations are compared with the results of process diagnostics. It is observed that axial emission profiles confirm the influence of the particle size on the evaporation behavior. Paper includes a German-language abstract.

Abstract This paper aims to characterise and to study several Ni-based alloys bond coatings and to determine the very best spraying conditions to achieve FGMs by means of a single gun with independent powder feed. First, adhesive layers made of NiCr, NiAl, and NiCrAlY were sprayed onto a steel substrate. All samples were tested by isothermal oxidation at 1000 deg C. The oxides formed and the conversions of the original oxides were studied on the samples and characterized using scanning electron microscope and EDS. It is observed that the study of three different bond coating sprayed with the same conditions reveals the best performance for the NiCr coating. Paper includes a German-language abstract.

Abstract Thermally sprayed coatings of high performance thermoplastics are of interest especially for the chemical industry for anti-corrosion applications at elevated temperatures. In this paper coatings of polyetherether-keton (PEEK) and polyphenylen-sulphide (PPS) have been produced by simple flamespraying. They have been investigated by optical metallography, FT-IR analysis and DSC-analysis. Among the coating properties also the "in-flight" particles have been studied by wipe-tests and FT-IR analysis in order to assess possible decomposition effects during spraying.

Abstract Polymer coatings find increasing interest for anticorrosion applications and others. Thanks to its extraordinary properties (high chemical stability, low creep rate and good electrical resistivity at relatively high temperature) PEEK (Polyetheretherketone) polymer is now considered as a challenging matierial. In this work, PEEK polymer powder was thermally sprayed with different processes. Particle impacts were observed and coating was analyzed by infrared spectrometry. The temperature of the substrate was shown to play an important role in the formation of dense and continuous coatings. Thermal degradation during spraying produces new carbonyl species due to chain scissions; but the amount of decomposition could be controlled from the choice of spraying conditions.

Abstract Amorphization induced by sliding wear and consequent wear resistance have been investigated in relation with the microstructure of Fe-Cr-B alloy spray coatings. The Fe-Cr-B spray coated layer exhibited much higher wear resistance and significantly lower friction coefficient in comparison with that of low carbon steel substrate thanks to the amorphous surface film formed during the dry sliding wear. Electron microscopy on the cross-section of the coated layer exhibited intra-particle segregation associated with rod-shape Cr rich (Cr,Fe)xB particles in the matrix of Fe-Cr solid solution phase. From the observations using TEM and EDS, Fe-Cr solid solution phase with super-saturated B and Si content was confirmed to be the phase which mainly contribute to the crystalline-to-amorphous transition induced by sliding wear. The formation of oxide inclusions seems to impede the crystalline-to-amorphous transition by lowering the solute content in Fe-Cr solid solution phase. Keywords : microstructure, wear-resistance, Fe-Cr-B alloy, amorphization, detonation gun

Abstract The transitional behavior of the splat pattern of Ni particles sprayed on a flat substrate was investigated. Based on Auger analysis and SEM observation, it was confirmed that the splashing was formed not by material flowing on the substrate surface from the impingement center to the periphery, but by jetting away from the central disk. Observations of etched splat surfaces revealed that the bottom portion of the central disk solidified rapidly after impingement, and it was also confirmed, based on the direction of the splash pattern, that the splashing was caused by stumbling due to some type of deterrent to liquid flow, such as poor wettability at the flow tip or initial rapid solidification of the splat. The drastic change of the splat pattern near the transition temperature seems to occur when the Weber number of the liquid flow coincides with some critical value.