Abstract
In thermal barrier coating (TBC) sprayed on the surface of high-temperature components in a land-based gas turbine (GT), stress is induced thermally or mechanically in the coating with the start-steady-stop operation of the GT. The coating stress leads to a crack initiation at the coating interface, and consequentially to TBC spallation. Thus, it is necessary to ascertain TBC interfacial strength, in order to assess precisely TBC spallation life. The aim of this study is to present the interfacial fracture toughness of TBC by using a TBC specimen exposed under a high-temperature environment. For accomplishing this, the fracture test is conducted using a mixed-mode interfacial fracture test device that has been proposed by our group. Thermal grown oxide (TGO) formation at the interface and residual stress of TBC, which are known as the origins of a reduction of the interfacial strength of TBC, also are examined. The intrinsic interfacial fracture toughness of TBC, which was estimated with the residual stress energy stored in TBC by thermal spray process, is related with cohesion of splat boundary and pore characterizing microstructure of TBC, in order to make clear why the TBC interfacial fracture toughness varied with exposure condition.
