An Approach to Prevent High-Cycle Thermo-Mechanical Fatigue Failures of Thermal Barrier Coatings

Structural reliability of thermal barrier coatings(TBCs) used in advanced land-based gas turbine power generation systems, has recently been increased year by year. This energy system has a specific advantage that it is flexible to absorb fluctuation in power supply from current renewable energy systems. However, the TBCs are frequently subjected to thermo-mechanical fatigue damages, because thermal stress is significant there. Here, understandings on not only the steady state thermo-mechanical fatigue (SS-TMF) failures but those on the non-stationary TMF (NS-TMF) failure have been essential. In the latter a special consideration should be taken to non-steady or transient thermal response of TBCs. In this work the failure behavior of NS-TMF were studied, in comparison with those of NS-TMF. The experimental works clearly demonstrated that the TBCs were subjected to additional damages under the NS-TMF. In order to insight this phenomenon, a simple mechanical model by which the transient thermal is passively taken into account has been proposed. The numerical calculation showed that the additional thermal stress is developed in the NS-TMF test, resulting in the additional damages in NS-TMF. Here the thermal stress showed peak under a given frequency, and the peak frequency was dominated by the physical and mechanical properties of TBS system and the Biot-number. Some suggestions were also discussed to avoid this type of new subject.