Abstract
Thermal barrier coating (TBC) of a gas turbine blade suffers from high temperature oxidation. Delamination damages of interface between ZrO_2-8%Y_2O_3 top-coating and CoNiCrAlY undercoating are reported. It is important to clarify the delamination mechanism. It is known that thermally growth oxidation (TGO) grows at the interface between ZrO_2-8%Y_2O_3 and CoNiCrAlY, and the TGO degrades the adhesive strength. The purpose of this study is to clarify the TGO growth process. Thermal aging tests of ZrO_2-8%Y_2O_3/CoNiCrAlY TBC systems under various temperature conditions were carried out. TGO growth process was observed by the electron probe micro analyzer (EPMA). Both TGO of Al and TGO of Cr were mapped, and the thickness of the TGOs were measured. Results are summarized as follows. (1) The delamination occurred at a ZrO_2-8%Y_2O_3 layer beside the interface. (2) The delamination occurred if the thickness of Al TGO layer increased over about 3μm. (3) The TGO of Cr didn't affect the delamination life, but affect the growth of Al TGO. (4) TGO growth rate was dependent of temperature. Taking into account of the temperature dependency, the thickness of Al TGO could be predicted with good agreement.
