Superior cyclic life of thermal barrier coatings with advanced bond coats on single-crystal superalloys

Abstract

Advanced thermal barrier coatings are essential to further increase the efficiency of gas turbine engines. One limiting factor of the TBC lifetime is the temperature dependent formation of the thermally grown oxide (TGO) during thermal exposure resulting in critical stress levels at the top coat-bond coat interface. Oxide dispersion strengthened (ODS) bond coats demonstrated slower oxygen scale growth during thermal exposure in comparison to standard bond coats.In this study for the first time TBC samples on single-crystal substrates (comparable to CMSX4) with thin ODS Co-based flash coats on the same Co-based bond coat (Amdry 995) and a porous atmospherically plasma sprayed (APS) yttria stabilized zirconia (YSZ) topcoat were manufactured by thermal spray techniques and evaluated with respect to their thermal cyclic behavior. As the major performance test cyclic burner rigs, which can establish thermal conditions similar to those in gas turbines, were applied.TBC samples with the new material combination show superior performance compared to previous samples. Cross sections of the samples were analyzed by scanning electron and laser scanning microscopy. Lifetime data and failure mode of the samples are discussed with respect to material properties such as thermal expansion coefficients, microstructural changes and TGO growth.