Evolution of thermal properties of EB-PVD 7YSZ thermal barrier coatings with thermal cycling

During high-temperature exposure, the microstructure of thermal barrier coatings evolves, leading to increased thermal conductivity. We describe the evolution in the thermal properties of a 7 wt.% Y2O3 stabilized ZrO2 electron beam-physical vapor deposited (EB-PVD) thermal barrier coating with thermal cycling between room temperature and 1150 °C until failure. The thermal diffusivity and conductivity of the coating were evaluated non-destructively based on the analysis of its photothermal infrared emission. Although the coating density does not increase significantly with thermal cycling, the thermal diffusivity and conductivity of the coating increased substantially, particularly during the first 20 1 h cycles. The values then approach a limiting value. Complementary Raman spectroscopy suggests that the increase is accompanied by a reduction in the defect concentration in the coating and that there is also a correlation between the width of the Raman lines and the thermal conductivity.