Manufacture and Properties of Segmented Thermal Barrier Coatings

Thermal barrier coatings (TBCs) made of yttria stabilized zirconia (YSZ) are frequently used in gas turbines to improve their efficiency. Coatings typically applied on combustion chamber parts with a thickness of more than about 500 |im often contain segmentation cracks. This type of cracks considerably improve the thermal cyclic life of the thick TBCs. Segmentation cracks can be directly introduced into the coatings during the plasma-spraying process. The influence of the most important process parameters as substrate temperature and passage thickness on the segmentation crack density will be described. In addition to the coatings with thickness values of about 1 mm, also thin coatings with segmentation cracks have been developed. This type of coating might also be favourable for an application on blades and vanes of gas turbines. The thermal cycling performance of all coatings was tested in gas burner test facilities. The thick, segmented TBCs almost reached the performance of conventionally sprayed thin TBCs. The thin, segmented TBCs showed an excellent performance at surface temperatures above 1300°C, which was considerably better than that of conventionally sprayed thin TBCs. Possible explanations for the observed improvement of the thermal cycling behaviour by the introduction of segmentation cracks will be given.