Secondary oxidation behaviors of refurbished EB-PVD TBCs specimens after different primary oxidation time

Abstract

The performance evaluation of refurbished thermal barrier coatings (TBCs) components is crucial for the engineering application of TBCs and prolonging the service life of high-temperature components. This work investigates the secondary oxidation behaviors of refurbished EB-PVD TBCs specimens after different primary oxidation time, including microstructures, thermally grown oxide (TGO) phase composition and TGO crystal structures. The results show that the γ phase coarsening occurs in the single-crystal superalloy substrate after primary oxidation before refurbishment, and this phenomenon is retained in the refurbished single-crystal superalloy substrate. Furthermore, the γ phase channel width increases with the increase of the primary oxidation time before refurbishment. The TGO of the refurbished specimens has a certain amount of θ-Al2O3 at the initial oxidation stage, and its content is positively correlated with the primary oxidation time before refurbishment. The TGO of the refurbished specimens is composed of Al2O3 doped with mixed oxides particles at the late oxidation stage. The TGO thickness of the refurbished specimens is higher than that of ordinary specimens under the same oxidation condition. There are a certain amount of micro-defects such as voids and cracks generated in the TGO of the refurbished specimens. Additionally, affected by the microstructures of the single-crystal substrate, the TGO of the refurbished specimens is equiaxial Al2O3, while the TGO of ordinary specimens is equiaxial Al2O3 at the top and columnar Al2O3 at the bottom.