Evaluation of graded thermal barrier coating for gas turbine engine

The degradation processes of the bilayer and 6-layer graded TBGs are discussed both experimentally and computationally. Transient thermal cycle tests using the hydrogen combustion gas burner showed that the surface layer of both types of coating spalled immediately after the initiation of heating; namely, the top coat was delaminated near the top coat/bond coat interface in the bilayer coating case, while the graded coating showed delamination at the boundary between the 100% stabilized zirconia layer and the adjacent 80% stabilized zirconia-20% MCrAlY composite layer. The maximum heat load to cause the top coat spallation of the graded TBG was clearly greater and the substrate temperature was 200 degree higher than that of the bilayer coatings. Finite element model analysis simulating the thermal cycle tests demonstrated that the top coat spallation of both types of coating is caused by the buckling driven by delamination due to the transient large in-plane compressive stress development immediately after initiate heating.