Investigation on hot-fatigue behaviors of gradient thermal barrier coatings by EB-PVD

Gradient thermal barrier coatings (GTBCs) have been produced by co-deposition of a tablet of mixtures of AlAl2O3ZrO2–8wt.%Y2O3 and an ZrO2–8wt.%Y2O3 ingot onto NiCoCrAlY bond coat by means of EB-PVD. Thermal cycling tests at 1323 K were conducted to evaluate the hot-fatigue behaviors of the coating. The microstructure and composition distribution of the coating was studied by SEM with EDS, and constituent phases identified by XRD. It was found that the gradient structure significantly increased the lifetime of the coating. Due to the selective oxidation of Al in the NiCoCrAlY bond coat and a Ni3Al film on the surface of the bond coat, an Al2O3 layer was developed between the bond coat and the transition layer. Failure of the gradient coating eventually occurred by cracking near the interface between the Al2O3 and transition layer. In addition, Compared with that before the test, the gradient coating after thermal cycling tests becoming softer than that before the test.