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.

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.