The role of bond coat oxidation for the lifetime of thermal barrier coatings

In order to raise efficiency and to reduce the CO₂ emission of land based gas turbines or aero engines, service temperatures should be increased. Even very complex cooling techniques are not sufficient to reduce the surface temperature of the metallic parts of first stage blades and vanes to a tolerable temperature level. In order reduce the surface temperatures a ceramic thermal barrier coating (TBC) can be applied on top of the oxidation resistant bond coat (BC). The service life times of these TBC systems are strongly influenced by the oxidation processes going on at the interface between the bond coat and the ceramic top coat. To take full advantage of the potential of such TBC systems, which means a design integration of the ceramic top coat demands for a reliable life time prediction. However, such life time prediction models that can ensure inspection intervals in excess of for example 25000h in the case of land based gas turbines are not yet available and research activities of all potential users are focused on the improvement of these life time prediction models.