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 Al ₂O ₃ is about five times larger than that of Al ₂O ₃, 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.