Thermal barrier coatings (TBCs) are essential for high-temperature components, such as turbine blades and vanes, to improve their heat resistance. Generally, thermal stresses are generated in the TBC systems with the thermal cycle due to the mismatch in the coefficient of thermal expansion (CTE) between the top coat (TC) and substrate. TBCs deposited by the air plasma spray technique (APS-TBC), most commonly used as the coating method for turbine blades and vanes, have the laminated splat microstructure, including many interlamellar pores and voids. The recently developed suspension plasma spraying (SPS) method can control microstructure and achieve a columnar structure that can relax thermal stress. However, improving the thermal shielding property in the SPS-TBC is required. Generally, yttria-stabilized zirconia is used for TC, but YbTa3O9(Yb) is attracting attention as an alternative material due to its excellent low thermal conductivity. A hybrid TBC using YSZ and Yb was proposed to improve the heat shielding properties of SPS-TBC. This study measured the thermal strain distribution on TBCs with four types of TC with different microstructures by Digital Image Correlation (DIC) method and experimentally evaluated relationships between microstructures and thermal strain. Based on these results, the effect of coating microstructure on thermal stress relaxation ability was discussed. The experimental results indicated that the column structure has excellent thermal stress relaxation ability compared with the laminated splat microstructure.
Takizawa et al. (Wed,) studied this question.