Influence of Thermal Aging on Interface Delamination of Thermal Barrier Coatings
Takamasa ONOKI, Tetsuro TONOMORI, Kazuhiro OGAWA, Toshiyuki HASHIDA, Tetsuo SHOJI, Masahide MARUYAMA, Hiroyuki TOGASHI and Taiji TORIGOE
Abstract:Knowledge of the degradation mode in thermal barrier coatings (TBCs) is a prerequisite for the prediction of their remaining life of gas turbine blades. This paper describes the effects of thermal aging on the microstructure in a YSZ-based thermal barrier coating system deposited on Ni based superalloy substrates. The heat treatment of the TBC specimens were conducted at 1373K for 100h, 500h and 1000h in air for thermal aging. The thermally aged coating system had thermally grown oxide (TGO) layer between the substrate and the TBC. TGO consisted of not only alumina but also other oxides. This oxide layer that named mixed oxides (MO) is composed of Ni, Co, Cr and O. Double cantilever beam (DCB) tests and 4 point bending tests were carried out in order to evaluate the TBC/substrate interface strength. The interface strength depended on the period of thermal aging in both type of tests. The interface strength increased initially up to the aging time of 100h, and then decreased drastically for the longer aging time. In DCB tests, crack propagated in the middle of YSZ layer for the thermally aged specimens, whereas delamination took place close to the YSZ-bondcoat interface in the unheated specimens. In 4 point bending tests, crack propagated along the interface between TBC and substrate. These results suggested that the interface strength depended on not only the formation of oxides but also the fracture properties of the top coatings. Key Words:Thermal barrier coating (TBC), Thermal aging, Thermally grown oxide (TGO), Double cantilever beam (DCB) test, 4point bending test, Interface strength