Effect of Microstructure on Ceramic Coating Durability

Garrett has conducted extensive burner rig characterization tests and developed engine-mission capable life prediction models for current generation EB/PVD and plasma-sprayed TBC systems under a NASA-sponsored program. Devel opment and calibration of this model are described in detail in reference 7. Burner rig specimen durability results indicate that the current generation EB/PVD coating is superior in a cyclic oxidation environment, relative to the best commercially available plasma-sprayed coating systems (Figure 9). In contrast, the current génération EB/PVD TBC system is also the most prone to molten salt film damage.

The TBC life model is designed to predict TBC lives as a function of engine, mission, and materials system parameters such as temperature, altitude (which controls sea salt ingestion), and turbine pressure (which increases the effective partial pressure of the ingested salts). Materials system parameters define the TBC system's resistance to ceramic-metal interfacial damage in a cyclic oxidation environment and molten salt film damage.

Predicted capability of the model for the EB/PVD TBC system (Figure 10), indicates that coating life is a function of temperature, aircraft altitude (or demister efficiency), and turbine pressure. Predicted lives of commerically-applied EB/PVD and plasma-sprayed TBC systems are shown in Figure 11 for business aircraft and maritime surveillance missions. It can readily be observed that the EB/PVD TBC system offers superior durability in a cyclic oxidation environment, which is characteristic of business aircraft and commercial airline missions. In contrast, severe TBC life reductions projected for EB/PVD TBCs are used in a maritime surveillance mission.

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