Comparative study on microstructure evolution and failure mechanisms of ordinary and refurbished EB-PVD TBC under cyclic oxidation

Abstract

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-Al 2 O 3 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.

CMAS Corrosion Behavior of Nanostructured YSZ and Gd-Yb-Y-Stabilized Zirconia Coatings

“…Thermal barrier coatings (TBCs) [1,2] are extensively utilized in gas turbines and aero engines to reduce the surface temperature of hot-section components and increase the turbine inlet temperature. The thermal spraying technologies for TBCs mainly include electron beam-physical vapor deposition (EB-PVD) [3] and plasma spraying [1,4]. A typical TBC consists of an 8 wt.% Y 2 O 3 -stabilized ZrO 2 (8YSZ) ceramic layer [5] and a MCrAlY (M = Ni/Co/Ni + Co) bond coat [6].…”