Abstract This paper examines the bonding mechanisms of high-speed flame spraying (HVOF) sprayed coatings on the basis of the experiments with the substrate at different surface roughness. In order to determine the dominant adhesion mechanisms of HVOF layers, the layers are applied to substrates of different roughness with completely melted powder particles as well as with powder particles with solid and liquid phases. The spray materials are NiCrBSi and WC-Co. The results of adhesion tests showed that the adhesion of the NiCrBSi layer on the roughened substrate was approx. 40 MPa, while there was no adhesion on the polished substrate. In contrast, the adhesive strength of the WC-Co layer on the polished substrate was already between 20 and 40 MPa. The adhesive strength of the WC-Co layers on the substrate with a roughness greater than 5.8 micrometer already exceeded that of the binder materials. Paper includes a German-language abstract.

Abstract The spreading and solidification of a molten droplet is governed a number of factors such as fluid inertia, viscosity, surface tension, surface wettability, heat transfer between the droplet and substrate, and surface thermal properties. Most numerical and experimental studies of droplet impact have considered a single molten droplet landing on a flat, solid surface. This paper investigates the sequential deposition of tin droplets with their centers offset using a three-dimensional model of droplet impact and solidification. The paper presents results from simulation of the successive deposition of two tin droplets onto a stainless steel substrate under conditions for which the experimental observations are available. Results from the model are compared with photographs of impacting droplets and found to agree well. Paper includes a German-language abstract.

Abstract This paper is devoted to the modeling of a plasma jet that hits a flat substrate surface as well as the modeling of its influence on the surface temperature during the layer build-up. In the first step, a two-layer structure according to the Chen-Kim-k-Epsilon model is incorporated into the PHOENICS Commercial CFD code. This model allows a simultaneous description of the turbulent plasma jet and the viscous sub-layers when the jet hits it. In a second step, the heat dissipation in the substrate is examined using a three-dimensional volume model based on the finite volume approximation. This two-part procedure allows the surface temperatures on the substrate to be determined during the layer build-up. Furthermore, the influence of the substrate properties is considered and discussed. Paper includes a German-language abstract.