Increasing the energy efficiency of plasma spraying by means of simulation-based process development

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Plasma spraying is one of the most important process variants in thermal spraying. At present, only a small part of the available energy is used to accelerate and melt the particles. A promising solution for increasing energy efficiency is a solid shroud that surrounds the plasma free jet and thus prevents mixing with the ambient air. As a result of this separation, the plasma temperature can be increased, thereby raising the energy efficiency. Another expected positive effect is the prevention of oxidation of the spray particles and thus the coatings.The primary goal of the project is to investigate the potential to increasing the energy efficiency of the plasma spraying process by using a solid shroud. In this project a methodology will be developed to design such a shroud and to optimize its geometry for given process parameters. Ideally, this solid shroud also increases the plasma stability of the plasma jet and thus the process stability. Therefore, a further goal is to investigate the effects of a solid shroud on the plasma stability. In addition to energy efficiency, a solid shroud also offers great potential for improving coating properties. Consequently, the possible influence on the coating properties will be investigated. In order to achieve these goals, a numerical simulation model of a plasma generator with a solid shroud will be developed based on a model of previous DFG projects. By using modern algorithms, such as particle swarm optimization and evolutionary algorithms, the geometry of the solid shroud is then calculated and optimized. The effects of the nozzle extension on plasma stability will be investigated by high-speed videography of the plasma free jet and high-resolution current and potential measurements. For these, appropriate measuring equipment is requested as part of this proposal. In experimental tests the effect on the energy efficiency and on the coating properties will be determined for the spray materials Al2O3 and MCrAlY.In the third year of the research project, a further approach to increasing energy efficiency, preheating of the spray particles, will be investigated. By exploiting the radiation of the plasma jet, the particles can be preheated without the need for an external source of energy. With the help of numerical simulations and experiments, such a preheating device will be designed and its potential to increase the energy efficiency will be determined. A combination of a solid shroud and a particle preheating will also be examined in detail this third year.