Entwicklung von Beschichtungsverfahren für die Herstellung von Wärmedämmschichten auf additiv gefertigten Komponenten

The protection of metallic combustion chamber walls and high-temperature blades in aircraft turbines by ceramic thermal barrier coatings (TBC) and air film cooling is crucial for increasing the efficiency and service life of the turbine. A further improvement in efficiency requires an increase in the gas inlet temperature, which necessitates the development of optimized WDS systems and cooling concepts. Additive manufacturing technologies facilitate the production of flow-optimized cooling holes, which form an insulating layer of air on the hot WDS surface using compressor air during turbine operation, thus protecting it from the hot combustion gases. However, to ensure a continuous air film, the cooling holes must not be blocked by the bonding agent layer (bond coat) or the top coat. The subsequent opening of complex geometries using mechanical processes or laser technology is time-consuming and cost-intensive, necessitating the development of suitable coating processes that avoid blocking the cooling holes. As part of this study, the propensity for blockage of several bond coat production techniques was assessed, including thermal spraying of a CoNiCrAlY alloy material using the High Velocity Oxygen Fuel (HVOF) process and vacuum plasma spraying (VPS). It was determined that the blocking issue in the HVOF process can be mitigated by modifying the spray angle between the torch and the substrate. Additionally, oxidation-resistant nickel-aluminide diffusion layers were produced on nickelbased alloys using the pack-cementation process, which effectively prevented blocking. Subsequent steps involved the coating of the samples using suspension plasma spraying (SPS) and plasma spray physical vapor deposition (PS-PVD). It was determined that the SPS process necessitates suitable pretreatment of the surface, such as sandblasting, to ensure stable bonding of the ceramic top layer. The results also demonstrated that the PS-PVD process is particularly effective in maintaining the cooling holes free, as it results in effective deposition from the gas phase, with most of the plasma gas flowing around the cooling holes. Moreover, both experimental and simulation-based evidence demonstrated that the SPS process can achieve reduced blockage compared to the APS process. In addition, it has been proven both experimentally and through simulations that the SPS process enables reduced blockage compared to atmospheric plasma spraying (APS). This is achieved by adjusting the spray parameters, such as the spray distance or the total gas flow rate, as well as the cooling air pressure. Thermal cycling tests have also shown that SPS and PS-PVD processes can be used to produce coatings with a comparable or even improved service life compared to APS coatings on substrates with cooling holes. This research project was financially supported within the framework of LuFo by the Federal Republic of Germany, Federal Ministry of Economics and Climate Protection, based on a resolution of the German Bundestag (FKZ: 20T1702) and by Rolls-Royce Deutschland Ltd & Co KG.