TGO Growth Behavior with Thermal Fatigue and Its Effect on Fracture Behavior of Thermal Barrier Coatings

Abstract

Growth behavior of thermally grown oxide (TGO) layer with thermal fatigue condition in thermal barrier coatings (TBCs) was investigated, including its effect on fracture behavior of TBCs and bonding strength of top coat. The formation of TGO layer was influenced by both temperature and time exposed. However, the TGO thickness was independent on the bond coat thickness (80, 140, and 280 µm) and the preparing method (APS and HVOF methods) of the bond coat. In Hertzian indentation tests for the TBCs before thermal fatigue, the TBCs with the bond coat prepared by APS showed fracture and/or delamination in regions of the top coat near to the interface, whereas the TBCs prepared by HVOF indicated cracks and fracture at the interface. After thermal fatigue, the fracture path passed along the TGO layer without any cracks created from Hertzian indentation within the top coat in both cases. The bonding strength of the top coat measured by adhesion tests shows lower values for the TBCs with the HVOF bond coat than those with the APS bond coat before thermal fatigue. However, the values are similar to each other after thermal fatigue. This result is attributed to the fracture path of the TBCs, depending on the TGO formation.