Design of gradient thermal barrier coatings

Gradient thermal barrier coatings (GTBCs) were prepared by co-deposition of a tablet of mixtures of AlAl₂O₃-YSZ and YSZ onto NiCoCrAlY bond coat by means of electron beam physical vapor deposition (EB-PVD). It was found that the microstructure is gradually transferred from metallic bond coat to YSZ topcoat and the composition distribution changes continuously with respect to the thickness of the coating. The coating exhibits a good resistance not only to high temperature oxidation but also to cyclic corrosion. A finite element numerical model was employed to study the stress developed in the coating during cooling. The results demonstrate that the Al₂O₃-YSZ graded layer provides a great reduction in the stress and stress gradient. The gradient layer is the crucial location that determines the lifetime of the gradient coating. The Al₂O₃-YSZ coating exhibited a lower thermal conductivity than traditional YSZ coating, which is caused by the microporous microstructure and the vacancies appearing in the ZrO₂ lattice.