Thermal Cycling Behavior of Thermal Barrier Coatings with HVOF NiCrAlY Bond Coat

Thermal Barrier Coatings with HVOF NiCrAlY Bond Coat is prepared on nickel-based superalloy substrates. The lifetime of the coating is about 1630 h for 1-h cycle at 1050 °C. Growth of the TGO (thermally grown oxide) approximately follows a parabolic kinetics, and the TGO presents a bi-layered structure. Failure of the coating occurs near the interface between the mixed oxides layer of TGO and top coat. A finite element method is employed to analyze the stress distribution in the coating. The results show that maximum stresses occur at the top coat/TGO interface near the edge of the coating. The maximum radial stress for TGO consisting of spinel and Al2O3 is about five times larger than that of Al2O3, while the maximum axial stress is about ten times larger. The mixed oxide layer of TGO plays an important role in the premature failure of TBCs.