Forschungszentrum Jülich GmbH
Columnar thermal barrier coatings (TBC`s) are characterized by their high strain tolerance and can be produced using various plasma spray processes, such as suspension plasma spraying process (SPS) or plasma spray-physical vapor deposition process (PS-PVD). Depending on the selected material and process parameters, the microstructure of the coating and its specific properties change. The thermal barrier coating is deposited on a CMSX-4 nickel-base superalloy substrate and CoNiCrAlY bondcoat, which results in a large mismatch in the coefficient of thermal expansion (CTE) between the metal and ceramic component. When the coating system is thermally cycled, this results in stresses in the system with radial components for rough bond coats, leading to premature failure of the thermal barrier coating. To reduce the CTE mismtach and the resulting local, out-of-plane stresses in the system, an oxide disperion strengthened (ODS) layer is applied between the topcoat and bond coat, which has a reduced coefficient of thermal expansion, compared to the substrate and bond coat. The use of this intermediate layer increases the lifetime of the coatings in so-called burner-rig tests. This technique applies a thermal gradient to the system and hence, simulates the thermal loading in a real gas turbine environment
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