Effect of microstructure on thermal cycle damage behavior of a TBC with YbTa 3 O 9 /YSZ dual top coating

Abstract

Thermal barrier coatings (TBCs) are widely employed in the hot sections of aero-engines and land-based gas turbines to improve thermal efficiency and extend the service life of superalloy components. Recently, the suspension plasma spray (SPS) technique, which deposits coatings using suspensions of submicron ceramic powders, has attracted increasing attention for fabricating columnar-structured yttria-stabilized zirconia (YSZ) top coatings with excellent thermal cycling resistance. However, further enhancement of thermal insulation capability remains an important challenge. To address this issue, ytterbium tantalate (YbTa₃O₉) has emerged as a promising top-coating material owing to its intrinsically lower thermal conductivity compared with conventional YSZ. In this study, dual-layered TBC systems composed of YSZ and YbTa₃O₉ were fabricated and systematically evaluated. Two types of coatings with distinct microstructures were prepared: (i) an APS-deposited YbTa₃O₉ layer with a lamellar microstructure on columnar YSZ (A-specimen), and (ii) an SPS-deposited YbTa₃O₉ layer with a dual-columnar structure on columnar YSZ (S-specimen). Thermal cycle fatigue tests, microstructural analyses, and in-situ digital image correlation (DIC) strain measurements were conducted to elucidate the effects of microstructure and interfacial diffusion on thermal durability. The results revealed that both dual-layered coatings exhibited markedly improved thermal fatigue resistance compared with conventional YSZ coatings, with the SPS-derived dual-columnar architecture showing the highest durability. The enhanced performance of the S-specimen is attributed to its strain-compliant columnar microstructure, effective stress relief through intercolumnar gaps, and interdiffusion-strengthened interfaces. These findings demonstrate that the integration of YbTa₃O₉ composition with SPS-derived columnar design provides a highly effective approach for developing next-generation TBCs with superior strain tolerance, adhesion stability, and thermal fatigue durability.