Abstract: Gradient thermal barrier coatings(GTBCs) were prepared by co deposition of a tablet of mixtures of Al Al 2O 3 YSZ and YSZ onto NiCoCrAlY bond coat by means of electron beam physical vapor deposition (EB PVD).It was found that the microstructure gradually transferred from metallic bond coat to YSZ topcoat and the composition distribution changed continuously through the thickness of the coating.The coating exhibited a good resistance not only to high temperature oxidation but also to cyclic corrosion.A finite element method numerical model was employed to study the stresses that developed in the coating as cooling from a stress free state at high temperature.The results demonstrate that the Al 2O 3 YSZ graded layer in the GTBC provided a large reduction in the stress and stress gradient.Furthermore,the gradient layer is the crucial location that determines the lifetime of the gradient coating.Additionally.the Al 2O 3 YSZ coating exhibited a lower thermal conductivity than traditional YSZ coating,which was caused by the micro porous microstructure in the coating and the vacancies appearing in the ZrO 2 lattice.

Key words: thermal barrier coatings ( TBCs), gradient coatings, electron beam physical vapor deposition ( EB-PVD), finite element, thermal conductivity