Investigation of thermal barrier coatings with different microstructures during thermal cycling with rapid cooling and heating

Atmospheric plasma sprayed (APS) thermal barrier coatings made of Yttria-stabilized zirconia (YSZ) have been used as thermal barrier coating in industrial gas turbines for decades. They improve component lifetime as well as turbine efficiency by enabling higher combustion temperatures. These coatings can have long lifetimes even at high combustion temperatures, however, fast transients have a negative effect on their performance. In the future, short cycles and hence load flexibility is becoming more important to compensate the fluctuations in energy supply caused by renewable energies. Therefore, the development of strain-tolerant coating systems with a simultaneously high insulation effect is essential. To achieve an optimal combination between these two properties, different coating systems were investigated. In addition to conventional APS coatings, highly porous APS coatings, coatings with segmentation cracks and columnar structured coatings were examined. To evaluate the coating properties, their microstructure, mechanical properties, and lifetime during thermal cycling with rapid load changes were compared. Furthermore, the stress states in the different coating systems were analyzed by recording the strains on the sample surface occurring during thermal cycling.