Effect of TGO Thickness on the Lamellar Interface Cracking in Plasma-Sprayed 8YSZ

摘要

There are a large number of non-bonded interfaces between ceramic lamellas. The non-bonded interfaces are equivalent to precracks in YSZ, which propagate and coalesce during thermal cycling, leading to spallation of YSZ coating. The thickening of thermally grown oxide (TGO) is inevitable during the turbine operation. The finite element analyses (FEA) showed that the residual stress in thermal barrier coating (TBC) increases with growth of TGO thickness. Moreover, the stress distribution in TBC is significantly influenced by TGO thickness. The tensile stress is present at the peaks and compressive stress at the valleys with thin TGO, while the nature of the stresses in the YSZ undulation valley reverses from compression to tension with a thicker TGO. These changes of stress distribution must lead to transformation of cracking tendency and location. In this paper, the gas burners with flame were used to carry out the thermal cyclic test giving a rather homogeneous temperature distribution on the sample surfaces. The influence of TGO thickness on cracking mechanism of TBC system under gradient thermal cycling was examined.