Thermal Aging Effect on In-Plane and Cross-Plane Thermal Diffusivities of Plasma-Sprayed Thermal Barrier Coating

Abstract

Thermal barrier coatings (TBCs) are used to shield from heat and wear of components which are used at high temperature situation, for example, the blades of gas turbines. There is a pressing need to evaluate the thermal conductivity of TBCs in the thermal design of advanced gas turbines with high energy efficiency. In the case of gas turbines, these TBCs consist of a ceramic-based top-coat (TC) and a bond-coat (BC) on a superalloy substrate. TBCs are commonly prepared by plasma spraying process. The TC is expected to play the role of a thermal shield. Thus, thermal conductivity of thickness direction of TBC has been investigated. However, plasma-sprayed TCs were known that they have anisotropic microstructure. We have been investigating in-plane and cross-plane thermal diffusivities of plasma-sprayed Yttria-stabilized zirconia (YSZ) TCs at 300 K in detail in a previous study. From the results of thermal diffusivity measurements for four kinds of TCs, it was found that plasma-sprayed TCs had significantly anisotropic thermal diffusivity depending on their microstructures. In this study, we measured in-plane and cross-plane thermal diffusivities of typical two plasma-sprayed TCs from 300 K to 1200 K in vacuum. And we also measured in-plane and cross-plane thermal diffusivities of annealed TC with different aging time. It was found that anisotropy estimated from in-plane and cross-plane thermal diffusivities did not change from 300 K to 1200 K. There was a tendency that thermal diffusivity value and anisotropy slightly increased by thermal aging effects.