Development and Optimization of Tailored Composite TBC Design Architectures for Improved Erosion Durability

Rare-earth pyrochlores, RE₂Zr₂O₇, have been identified as potential thermal barrier coating (TBC) materials due to their attractive thermal properties and CMAS resistance. However, they possess a low fracture toughness which results in poor erosion durability/foreign object damage resistance. This research focuses on the development of tailored composite air plasma spray (APS) TBC design architectures utilizing a t′ Low-k secondary toughening phase (ZrO₂-2Y₂O₃-1Gd₂O₃-1Yb₂O₃; mol.%) to enhance the erosion durability of a hyper-stoichiometric pyrochlore, NZO (ZrO₂-25Nd₂O₃-5Y₂O₃-5Yb₂O₃; mol.%). In this study, composite coatings have been deposited with 30, 50, and 70% (wt.%) t′ Low-k toughening phase in a horizontally aligned lamellar morphology which enhances the toughening response of the coating. The coatings were characterized via SEM and XRD and were tested for erosion durability before and after isothermal heat treatment at 1100 °C. Analysis with mixing laws indicated improved erosion performance; however, a lack of long-term thermal stability was shown via isothermal heat treatments at 1316 °C. An impact stress analysis was performed using finite element analysis of a coating cross section, representing the first microstructurally realistic study of mechanical properties of TBCs with the results correlating well with observed behavior.