Simulation Supported Process Development for the Deposition of MCrAlY Coatings by Means of the AC-HVAF Process

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The AC-HVAF process (Activated Combustion High Velocity Air Fuel) is one of the process variants of the thermal spraying. The particle in flight characteristics, such as the particle velocity and temperature, are crucial for the properties of thermally sprayed coatings. The AC-HVAF process can close the gap between the High Velocity Oxygen Fuel (HVOF) and Cold Gas Spraying (CGS) process regarding the particle velocity and temperature. It results in a combination of the particle velocity and temperature that leads to a low porosity and oxide content in the deposited coatings, which makes the AC-HVAF process a potential process for applying high-quality MCrAlY coatings, where M stands for nickel, cobalt or their combination. The reported high energy efficiency of the AC-HVAF process in the literature, due to the high deposition rate and deposition efficiency, is a further advantage of the AC-HVAF process. However, the use of the process is still relatively limited due to a lack of process understanding. The particle in-flight characteristics are determined by the combustion process and the gas flow. The majority of these processes takes place inside the spray gun and nozzle, where direct measurement is difficult. Computational fluid dynamic simulation is an efficient tool for overcoming this difficulty. The aim of this research project is the development of suitable AC-HVAF processes, which enable the deposition of high-quality MCrAlY coatings, with the support of CFD (Computational Fluid Dynamics) simulation. The development of the CFD model begins with the analysis of the spraying processes for a fine and a coarse CoNiCrAlY feedstock material. Different aspects regarding the mashing strategy and the combustion model will be considered. The particle velocity after the nozzle exit will be measured using particle diagnostic systems to validate the developed CFD model. The process parameters will be varied systematically in order to verify the applicability of the model under various process conditions. The model will further be used to develop the spraying processes for NiCoCrAlY feedstock materials, which enable the further validation of the applicability of the CFD model. The model will be thereby, if necessary, further developed. The coating properties –porosity, oxygen content, and roughness – of chosen coatings and their behavior under isotherm conditionings will be investigated to reveal the correlation between the coating properties and the process parameters or the process condition. This investigation enables a profound understanding of the AC-HVAF process.