Abstract
The change of microstructure in an atmospheric plasma sprayed thermal barrier coating (APS-TBC) by isothermal heat exposure has been studied. Used 8 mass%Y2O3-ZrO2 TBC layer, a Ni-Co-Cr-Al-Y bond coat (BC) layer, and an IN738 superalloy substrate. The TBC system is subjected to heat exposure at 1423 K in ambient air for 10, 50, 100, 200, 300, and 400 h. Polished transverse sections of heat-exposed TBCs are examined and the changes of constitutes are discussed. Both sintering and cracking of the TBC layer are observed and these behaviors are strongly correlated with the morphology of as-sprayed intersplat boundaries and heat exposure time, respectively. A thermally grown oxide (TGO) layer is formed after heat exposure, and the thickness increases with the increase in heat exposure time. The chemical composition and morphology of the TGO layer depend on the heat exposure time. Micro-cracking in the TGO layer and TBC layer is observed after formation of a spinel, which is attributed to a lack of Al in the BC layer. The composition and phases in the BC layer are strongly correlated with the growth behavior of the TGO layer.
