In this work several powder materials typically used for wear and corrosion protection (WCCoCr, Cr 3 C 2 NiCr, Cr 2 O 3 ) were considered for developing near net shape coatings. In contrast to grain sizes commonly used in thermal spray processes the grain sizes of all examined powders were specified with maximum 25 µm (-15+5 µm, -20+5 µm, -25+5 µm). During the coating experiments the HVOF process was used to apply carbide based powder materials (WCCoCr, Cr 3 C 2 NiCr) whereas the APS process was used to deposit Cr 2 O 3 coatings. Taguchi techniques were utilized in order to reduce the number of experiments and to evaluate and to adjust main process variables. The effectiveness of these techniques could be verified by spraying validation samples successfully. The coatings were examined in terms of deposition efficiency, surface roughness, hardness, porosity, wear and corrosion resistance. The results showed that improvements in terms of porosity, surface roughness and corrosion resistance could be reached by introducing fine powder materials in the spray process. Reducing the influence of effects like decarburization or oxidation caused by the overheating of small spray particles should be considered in future work.

The disadvantage of plasma torches using conventional single cathode techniques is the occurrence of azimuthal and axial instabilities inside the plasma torch. This causes electrical power fluctuations which result in inhomogeneities of the plasma jet enthalpy and with that an uneven plasma particle interaction. Hence, variations in particle properties occur and consequently an uneven coating quality is produced. Using the triple-cathode technique these electrical power fluctuations were successfully reduced, resulting in a stationary plasma flow. Thus this technique appears to offer the potential to homogenize coating properties. Similar results have been shown for plasma torches with triple anode arrangements. The goal of this research group is to homogenize properties of plasma sprayed coatings using of 3-cathode and 3-anode technologies based on numerical simulations. The approach used is to subdivide the complete APS process into the areas plasma torch, free jet as well as coating formation and characteristics. By simulation of the individual areas and combination with experimental results the corresponding process parameters will be obtained for the desired coating properties.

New requirements for modern component part surfaces increasingly demand improvements over friction coefficients in the sense of a reduction of friction losses. A substantial control factor in terms of lower friction and wear is the use of coating solutions such as thermal spray coatings. In practice, the application of coatings by means of thermal spray is more and more often used for influencing tribological matching. However, surface microstructuring might represent an additional, further reaching solution for wear and friction behaviour improvements of tribologically high-stressed surfaces. The aim of the reported research project is the development of atmospheric plasma sprayed (APS) coatings with an inherent porous microstructure and surfaces with stochastically distributed nap volumes (from cut pores) regarding lubricant retention and -distribution in running surfaces of friction-type bearings. Subject of these investigations are in particular thermomechanically highly loaded hydrodynamic tribological matchings, amongst others by the example of a piston ring/cylinder system in engine blocks. The use of special fractioned Fe-base powders enables the production of a new type of coatings with an inherent porous microstructure, which offer advantages due to constantly regenerating their surface topology under wear, and maintain employment in tribological systems with increased loads due to optimized lubricant retention and distribution. Hence, this project has an emphasis on the design of optimal nap sizes in coating surface structure in dependence on the hydrodynamical load, as well as on investigations for the controllability of nap volumes by the design of suitable processes.

Near net shape coating is a trend in thermal spraying being aimed at for several years to lower costs through shortened spray time and reduced after treatment work. Because of better microstructure compared to conventional coatings, the thickness is often also reduced. To characterise the quality of those thin layer systems the standardized tensile adhesive test is not suitable, as the adhesion outweighs the cohesion by far due to reduced quantities of coating defects. To characterize the coatings behaviour under tensile stress, three-point bending tests were performed. As especially thin cermet coatings do not show abrupt catastrophic failure in bending tests, ultrasonic signals being emitted from cracks propagating through the coatings were taken during the tests. Three coating systems (Cr 2 O 3 , Cr 3 C 2 -NiCr and WCCoCr) were investigated in this work using fine grained feedstock powders with three different size distributions per system. The tests showed the negative influence of stress moments in case of the oxide ceramic and the embrittlement of the cermets, especially the Cr 3 C 2 -NiCr, with increasing spraying temperature regime due to increased formation of solid solutions and decarburization. It can be said, that the analysis of acoustic emission during bending tests gives valuable information about how to achieve thin wear and corrosive protecting coatings being qualified for high operational demands.

The use of diamond-impregnated tools for the machining of any type of building material or natural stone is an established technology. Sintering and brazing are the key manufacturing technologies. The restricted flexibility of the geometry variation, the absence of the repair possibilities of damaged tool surfaces as well as difficulties in controlling the materials interfaces are some drawbacks. Therefore, manufacturing diamond tools through new technology concepts are required not only to avoid these restrictions mentioned but also to enhance the tools properties. In particular, thermal spraying technologies can act as a potential problem solver due to their special technological properties. Especially the new high-speed technologies such as the detonation-gun and high velocity oxygen fuel thermal spraying are promising approaches. Through these technologies, it is possible to control the kinetic energies of the diamond particles as well as their temperature during coating. In this report, a novel manufacturing technology of the diamond-impregnated tools based on these high-speed thermal spraying technologies will be reported. The layer properties will be evaluated with respect to the diamond quality after coating and with respect to the properties of the diamond composite coatings. Diamond spraying efficiency, diamond distribution in the layer as well as diamond-metal binder-interaction are analysed.