The present study investigates the influence of spray torch handling parameters such as the spray angle, spray distance, track pitch, and gun velocity on the deposition rate and the deposition quality of Atmospheric Plasma Sprayed WC-12Co coatings as well as Twin Wire Arc Sprayed WSC-Fe coatings. Based on results of light microscopical analysis similarities as well as fundamental differences in the sensitivity of the two spray processes, regarding changes in handling parameters, are discussed. Both coating systems show distinct changes of the deposition rate when varying the handling parameters. An empirical model could be determined to describe the coating deposition. This model enables an optimization of path planning processes by reducing the number of optimization loops. However, the coatings show visible changes in the microstructure, which have to be taken into consideration in order to guarantee the production of high quality coatings.

The interaction between thermal spray parameters and coating characteristics of atmospheric plasma sprayed WC-12Co was investigated by means of statistically designed experiments. A central composite design was employed to study the influence of the process parameters’ ratio Ar/H 2 , plasma gas volume flow, powder feed rate and stand-off distance on the deposition efficiency, tensile strength, porosity, roughness, particle temperature, particle velocity and the percentage of molten carbides. The process parameters’ volume flow and powder feed rate showed a considerable impact on the microstructure and morphology of the coatings, which could be traced back to a change in the melting degree of the powders as well as a change in particle temperature and velocity. On the basis of the statistical experiments, mathematical expressions were found to describe the coating characteristics. The quality of the mathematic model was scrutinized in a subsequent evaluation stage.

Computer simulations of thermal spray coating processes can accelerate the development of new products by minimizing the need for prototypes. An important aim of these simulations is the calculation of the coating distribution on the surface of a given workpiece with respect to a given movement path of the spray gun. In this paper, a novel approach for computing coating distribution on arbitrarily complex freeform surfaces is presented. In contrast to approaches that implement symmetric deposition models, the presented concept is based on a rotationally asymmetric model, making it particularly well suited for wire arc spraying as turbulences caused by electrodes in the gas flow often result in asymmetric coating distributions. In order to obtain the required knowledge base to derive the deposition model and verify the simulation, basic experiments were made. The simulation concept and experimental setup are presented in the paper along with the results.

Thermal spray coatings produced from hard materials show good potential for extending the service life of sheet metal forming tools. However, post-process methods currently used to improve coating surface quality are slow and expensive, especially on complex surfaces. A novel approach, demonstrated in this study, is the optimization of thermally sprayed coatings by roller burnishing. This process shows a high potential to not only reduce surface roughness and porosity, but also increase hardness even on free-formed surfaces. In the experiments, atmospheric plasma-sprayed CrC-NiCr coatings were produced and the burnishing process was performed on a CNC milling machine. Both the spraying and surface finishing processes are described and the results are presented and discussed.

This paper presents an investigation of the influence of the spray angle on thermally sprayed coatings. Spray beads were manufactured with different spray angles between 90° and 20° by means of atmospheric plasma spraying (APS) on heat-treated mild steel (1.0503). WC-12Co and Cr 3 C 2 -10(Ni20Cr) powders were employed as feedstock materials. The spray beads were characterized by a Gaussian fit. This opens the opportunity to analyse the influence of the spray angle on coating properties. Furthermore, metallographic studies of the surface roughness, the porosity, the hardness and the morphology were carried out and the deposition efficiency as well as the tensile strength were measured. The thermally sprayed coatings show a clear dependence on the spray angle. A decrease in spray angle changes the thickness, the width and the form of the spray beads. The coatings become rougher and their quality decreases. In addition, the spray process becomes inefficient as the deposition efficiency declines. Especially, below 30° for Cr 3 C 2 -10(Ni20Cr) and below 50° for WC-12Co a significant change in microstructure was observed.