The future demands of diesel engines require new options for low-friction and wear-resistant materials in order to increase efficiency and achieve environmentally sound solutions. Efforts are made to improve the performance and reduce the weight of engine blocks by coating the Aluminium cylinder bores with thermal-spray processes. Thus beside other means today nanocrystalline coatings are currently discussed, which should allow for the desired combination of structural, productional, and topographical properties. Beside sufficient tribological properties it is important that the composite (base material and coating) allows for an elongated endurance under cyclic mechanical and thermal stresses. In this work a four-point-bending test was used to examine deleterious failure mechanisms during fatigue such as spalling of the coating or delamination from the substrate. Therefore various thermally sprayed coatings were bent in tension and compression. The results were analysed in relation to the coating microstructure.

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 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.

Nitrogen-alloyed steels have outstanding properties, but are rarely used in thermal spraying. In this study, high-nitrogen duplex and austenitic steels are sprayed using APS and HVOF techniques and the resulting layers are evaluated based on microstructure, composition, and corrosion and wear properties. HVOF layers outperformed the APS layers in corrosion and wear testing, with austenitic steel having the highest corrosion resistance, and duplex steel the highest wear resistance. Paper includes a German-language abstract.

Studies on atmospheric plasma spraying have generally focused on the influence primary parameters such as gas flows and plasma current. However, the APS process is also influenced by a large number of disturbance variables including electrode wear, cooling system irregularities, and disruptions in powder injection. This study investigates both the cause and effect of each of these factors in the context of aluminum oxide spraying. Numerous measurements are made showing how electrode wear, cooling fluctuations, flow measurement inaccuracy, and variations in powder feed rates affect in-flight particle characteristics, deposition efficiency, and layer thickness. Paper includes a German-language abstract.

This paper presents research highlights obtained over the past three years in the course of a DFG-funded project on new and emerging diagnostic methods for thermal coating. It describes the tools and techniques used, the particle and substrate variables monitored, the accuracy of each measurement, and various associations with coating properties. Paper text in German.

This work concerns the production and use of aluminum oxide-NiCr dispersion powders for thermal spraying. It investigates the morphology and hardness of the powders and the microstructure and wear resistance of the resulting coatings. The powders are prepared by high energy ball milling and are used to produce oxide dispersion strengthened NiCr coatings via HVOF spraying. Among the key findings is that the powders are less homogeneous when milled with nanoscale aluminum oxide as are coating properties. Paper includes a German-language abstract.

The aim of this study is to investigate the development of thermally sprayed coatings for thixoforming dies and assess the effects of hot isostatic pressing on plasma sprayed coatings applied to TZM, stainless steel, and hot work steel substrates. As-deposited and compacted layers are analyzed with regard to their suitability for thermal, mechanical, and chemical protection. Paper includes a German-language abstract.

Microplasma spraying has the potential to expand the range of applications for plasma spraying, particularly for the production of functional coatings. The low heat input on the substrate material allows small and thin-walled components to be coated without risk of overheating or deformation and with less powder loss due to the small plasma jet. This paper investigates the influence of various process parameters on the spraying of molybdenum, stainless steel, WC-Co, zirconium dioxide, and aluminum oxide using a microplasma system. Material consumption, plasma jet size, and layer structure are measured along with various aspects of particle behavior in the plasma jet. Paper includes a German-language abstract.

Supersonic, two-phase flow of a gas/particle mixture directed towards a substrate may enable the deposition of "cold" particles onto a "cold" substrate under certain conditions. The method is commonly known as Cold Gas Dynamic Deposition or Cold Spray. Current research shows that copper can be deposited within a wide range of parameters and velocity regimes, whereas the deposition of other materials may involve difficulties depending on the material properties and substrate characteristics. Although particle velocity is recognized as being the key factor in the deposition of particles with the cold spray process, it alone cannot describe the state of the particle prior to and during impact. A simple analysis shows that the impulse of particles with equal particle velocity and size depends significantly on its density. For common engineering metals, an interval varying by up to a factor of 5 is possible considering, for example, magnesium and molybdenum. The impact force, directly dependent on the particle's impulse, governs the pressures generated during impact. In a simplified calculation, pressure values of around 3000 MPa can be very easily determined. While the particle impulse accounts for the degree of interaction - partial or complete deformation - the particle's and the substrate's lattice structure and its capacity to deform determine the type of particle substrate interaction. Depending on these properties, the substrate, the particle or both will be deformed. Evaluating impact experiments shows distinct differences between the impacts of copper, steel and aluminum particles on aluminum and steel substrates. The paper presented may be seen as a contribution to the discussion of a theory to evaluate coating and substrate combinations prior to spraying in order to predict bonding and coating build-up or to offer guidance concerning the optimum parameter set for deposition.

Thermal spray technology became established in various parts of industry (e.g. aircraft industry, medical industry etc.). Some of the applications are highly sensitive, therefore the coating quality plays an important role. Most of the common quality control methods are based on destructive testing methods which are undesirable for economical reasons. In recent years the interest in non-destructive online measurement methods increased and still is growing. More detailed knowledge of the relationship between process parameters can help to improve the coating quality standards and to understand different phenomena in thermal spraying. This will make online process control possible and improves the acceptance of thermal spray technology. In this paper results of fundamental studies on the atmospheric plasma spraying process (APS) are presented. Al 2 O 3 and NiCr powder were sprayed as model materials. In the experiments modem on-line monitoring systems were used to investigate the entire process from gun parameters to the coating quality. The faces in this paper are set on investigations of the in-flight properties of spray particles with the particle sensor DPV 2000 and their relationship with resulting coating properties. A method will be presented to extract characteristic values (velocity and temperature) out of the spray process with DPV 2000. With this method the APS-process was monitored and process parameters were correlated with main coating properties.

The processing of metallic alloys with the atmospheric HVOF process requires a uniform setting of the particle parameters, particle temperature and velocity, as these determine the tendency towards oxidation and the flattening behavior of the particles. Using the example of a NiCr alloy, this paper examines the effects of different particle diameters of a typical HVOF grain fraction on the achievable uniformity of processing. In addition, particle parameters are correlated with the process variables fuel gas composition and spray distance as well as the resulting application efficiency in order to determine whether they can be influenced. The particle properties of surface temperature and speed are characterized with the aid of a high-speed particle pyrometer. It is shown how, with the help of this particle diagnosis, an on-line process control can be used as proof of quality assurance. Paper includes a German-language abstract.

Thermally sprayed coatings made of polyetheretherketone (PEEK) and polyphenylene sulfide (PPS) are becoming increasingly interesting, especially for corrosion protection applications at elevated temperatures in the chemical industry. In contrast to conventional polymers these materials melt at much higher temperatures. Furthermore, PPS and PEEK show enhanced mechanical and chemical stability. Instead of HVOF and plasma spraying, in this paper much simpler and low-cost flame spraying is used because of these advantages. The polymers are investigated along the entire deposition process in order to exclude possible decomposition. Attempts are made with various adhesive layers to reduce the unacceptably high preheat temperatures. The corrosion protection features are examined by means of corrosion tests with various media. The results of the experiments presented in this paper promise coatings of high performance thermoplasts a great future as anticorrosive coatings. Paper includes a German-language 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.