The Evolution Behavior of Temperature Distribution and Sintering of Ceramic Top-coat Induced via Delamination Crack Propagation in Thermal Barrier Coatings

The work aims to research the influence of temperature distribution and sintering behavior of yttria-stabilized zirconia (YSZ) coating over the delamination crack propagation in atmospheric plasma spraying thermal barrier coatings (APS-TBCs). The finite element model (FEM) was used to analyse the temperature distributions of YSZ coating above the delamination crack with different sizes, and the sintering behavior of YSZ coating was examined via gradient thermal cycling test. scanning electron microscopy (SEM) was employed to analyse the microstructure of the surface and the cross section of YSZ coating. The image method was used to analyse the porosity of YSZ coating. The results show that the high-temperature area of the YSZ coating depends on the crack size, and the highest temperature is always on the surface of the YSZ coating above the crack center. The temperature decreases from the crack center to its tip. In this case, the maximum temperature across the thickness of the coating increases linearly with increasing of the delamination crack size. The temperature at the same position above the YSZ coating increases by about 30 ℃ when the crack size increases 0.5 mm. The maximum temperature region increases. When the crack length exceeds 3 mm, the temperature in the YSZ coating region above the crack increases due to the thermal barrier effect of the delamination crack. The temperature of the whole YSZ coating above the crack increases with the length of the crack, which not only leads to the increase of the area where the YSZ coating undergoes phase transformation and sintering, but also increases the phase transformation and sintering rate. The number and length of delamination and vertical cracks on the surface and inside of YSZ coating are different under different thermal cycles, and the sintering area increases gradually. The maximum width of the delamination crack is about 40 μm, corresponding to the 4 mm crack. The temperature of YSZ coating above the delamination crack decreases radially from the center to the tip. The layered structure and the porosity of YSZ coating disappears gradually from the interface to the free surface of the YSZ coatings. Thus, the sintering and phase transformation degree of the corresponding area is gradually increased, furthermore, the possibility of coating failure is further increased. © 2021, Chongqing Wujiu Periodicals Press. All rights reserved.