Refurbishment of thermal barrier coating (TBC) has become a valuable technique to prolong the service life of high-temperature components. This study investigates the effect of the refurbishment process (coating removal and recoating) on the microstructure evolution and physical properties of TBC, including oxidation characteristics, element diffusion behavior, and crack failure mechanisms. The results showed that a certain amount of interdiffusion zone (IDZ) with Cr-rich would be retained in DD6 superalloy substrate after coating removal. The microstructure of the refurbished specimens showed equiaxed β-NiAl phases, while the ordinary specimens have elongated grain shapes with a high aspect ratio. Moreover, mixed oxides in the refurbished TBC specimens were earlier observed during cyclic oxidation, with a greater thickness compared to ordinary TBC, due to the influence of BC layer phase sizes. The growth mechanism of thermally grown oxide (TGO-Al₂O₃ layer) in the refurbished TBC specimens was also different, resulting from the different mechanisms of mixed oxides growth. Furthermore, under cyclic oxidation with water quenching at 1100 ℃, the cracks in the refurbished specimen tend to occur in the mixed oxides layer, while the cracks in the ordinary specimen occur in the top coat (TC) layer, attributing to the earlier and thicker mixed oxides layer formed in refurbished specimens.

Calcium–magnesium–alumino–silicate (CMAS) corrosion is a critical factor which causes the failure of thermal barrier coating (TBC). CMAS attack significantly alters the temperature and stress fields in TBC, resulting in their delamination or spallation. In this work, the evolution process of TBC prepared by suspension plasma spraying (SPS) under CMAS attack is investigated. The CMAS corrosion leads to the formation of the reaction layer and subsequent bending of TBC. Based on the observations, a corrosion model is proposed to describe the generation and evolution of the reaction layer and bending of TBC. Then, numerical simulations are performed to investigate the corrosion process of free-standing TBC and the complete TBC system under CMAS attack. The corrosion model constructs a bridge for connecting two numerical models. The results show that the CMAS corrosion has a significant influence on the stress field, such as the peak stress, whereas it has little influence on the steady-state temperature field. The peak of stress increases with holding time, which increases the risk of the rupture of TBC. The Mises stress increases nonlinearly along the thick direction of the reaction layer. Furthermore, in the traditional failure zone, such as the interface of the top coat and bond coat, the stress obviously changes during CMAS corrosion.