Eb Nano-structured On-the Pvd Zirconia Thermal Barrier Coatings Research

The Thermal Barrier Coatings (TBCs) is one of the key technologies to develop high performance aero-engines. The applications of TBCs on turbine blades might lead to efficiency improvements by allowing a reduced cooling air flow at a given operating temperature, improve lifetime of the components by reducing the operating temperature at a given cooling air flow, or increase the thrust-to-weight ratio of the engine by allowing higher inlet temperature. The goals of developing the advanced TBCs are to increase its operating temperature, enhance its thermal barrier effect, and prolong its service lifetime.The performance of TBCs can be greatly affected by their microstructures. Therefore, it is feasible and effective to improve the property of TBCs through modifying the microstructure. The objective of this thesis is to develop nano-structured TBCs by electron beam physical vapor deposition (EB-PVD), in order to exploit the full potential of the widely used YSZ (ZrO2-8wt%Y2O3) TBCs.The nano-structured YSZ top layer was produced by using a special ceramic ingot as evaporation source charge. The ceramic ingot was made of YSZ powders in size of nanometer. With the high surface to volume ratio of the ceramic particles, this source material can be evaporated at higher speed under a relatively lower EB power. It resulted in high deposition rate and low condensation energy to promote the formation of nanostructural features in the coating, and the formation of fine columnar structures at a reduced deposition temperature accordingly, as well.The detailed microstructure of the coating was studied by SEM and TEM. The characteristic of the nano-structured coating was of fine columns with nano- grains and pores. A thin layer of thermal grown oxide (TGO) in 20nm thickness was detected between the ceramic coating and the metallic bond coating in the as-deposited TBCs.In comparison, the nano-structured TBCs showed a better thermal barrier effect than that of the conventional one under the same testing condition. When the environmental temperature of the hot gas is 1100℃, the flow of the cooling air is 3.8m3 /h, the thermal barrier effect of nano-structured TBCs of 150μm in thickness was measured to be 115℃.The durability of the nano-structured TBCs was estimated through thermal cycling test, which consisted of repeatedly heating the sample in air to 1100℃and maintaining that temperature for 30 minutes, followed by 5 minutes air cooling. The nano-structured TBCs sustained 800 cycles without any visible change. The ultimate failure of nano-structured TBCs occurred at the interface of TGO and bond coat.