Failure mechanisms during thermal cycling of plasma sprayed Zr{sub}O{sub}2-Y{sub}2O{sub}3 TBC's and the effect of a pre-oxidized NiCrAlY bond coat

摘要

The failure mechanism of thermal barrier coatings (TBCs) subjected to a thermal load is still not entirely understood. Thermal stresses and/or oxidation cause the coating to fail and hence must be minimized. We sprayed TBCs up to 1.0 mm with a high intrinsic strength, withstanding the high thermal stresses during thermal cycling and lowering the interface temperature. Further more, we gave the bondcoat a pre-oxidizing treatment before applying a topcoat. The bond strength and the behavior during three different thermal loads of the pre-oxidized TBCs are compared with a standard duplex TBC. With FEM-calculations the occurring stresses during thermal shock are calculated. Bondcoat oxidation and interface roughness are implemented. It is concluded that the TBCs, applied during this research, exhibit excellent thermal shock resistance and that a pre-oxidizing treatment of the bondcoat increases the lifetime during thermal loading. The FE-model gives a first impression of the failure mechanisms during thermal loading, but further development is required.