Chemo-thermo-mechanical modeling of EB-PVD TBC failure subjected to isothermal and cyclic thermal exposures

The thermal barrier coatings (TBC) are working under chemo-thermo-mechanical loading conditions and the failure process is characterized by complex aluminum migration, oxidation reactions and cyclic thermo-mechanical degradation. In the present work, the aluminum migration in EB-PVD TBCs subjected to isothermal and cyclic thermal exposure was studied and integrated into fracture mechanics description of the TBC system failure. Experimental and analytical investigations revealed that the damage of the TBC cannot be uniquely characterized by the thickness of the thermal growth oxide layer (TGO) and is furthermore related to the chemical reactions around TGO as well as evolutions of residual stresses. The expansion of the TGO played a key role in the mechanical performance of TBC. It was confirmed that the residual stress evolution is linearly correlated with the rumpling surface length of the TGO layer. Failure of the TBC system was characterized by degradation of the TGO interface and increment of residual stresses. A life model was developed based on the concept of the fracture toughness depending on interface degradation and residual stress evolution.