Fractographic study of adhesion tested thermal barrier coatings subjected to isothermal and cyclic heat treatments

Thermal barrier coatings (TBC) are used in gas turbines to protect metallic components from high temperature. In the present study adhesion tests have been conducted on APS TBC coated specimens subjected to different heat treatments. Isothermal and cyclic heat treatments have been conducted at temperatures around 1100 °C and the adhesion have been tested using the method described in ASTM C633. The fracture surfaces resulting from the adhesion test have been investigated and the fracture behavior has been characterized. A difference in fracture mechanism between the three heat treatments has been found. The two cyclic heat treatments give fracture in the top coat/bond coat interface while isothermal heat treatment gives fracture in the top coat.