Functional Evaluations for a Vertical-Crack Induced Thermal Barrier Coating System
Masayuki ARAI, Uichi IWATA, Tatsuo SUIDZU and Kazumi TANI
Abstract:Recently, metal temperature of combustor and blade in a land-based gas turbine is increasing with inlet gas temperature, in order to improve the thermal efficiency. Thus, thermal barrier coating (TBC) technology is applied to the surface of these hot parts for reducing the metal temperature. Advanced TBC materials and its processing technology such as functionally graded TBC and electron beam deposited TBC had been developed for these demands. But, application of these developed TBCs to the actual turbine blade was found to be difficult, because of a high cost of the processing machine and so on. In this study, advanced TBC with vertical crack in the top coating layer (vertical-crack induced TBC) was tried to fabricate by using a combination of conventional thermal spray technology and the special heat treatment. Then, the material properties, such as thermal stress variation of the TBC during thermal cycling, bonding strength between the top coating and bond coating and the interface oxidation process, were examined. Through some material evaluations for the vertical-crack induced TBC, it was found that the thermal stress in the top coating, which is caused during thermal cycling, is very lower than one of a conventional TBC. The bonding strength of the vertical-crack induced TBC is also higher, and then its TBC interface oxidation thickness is very thin. The vertical-crack induced TBC, which was evaluated here, was found to be superior to the conventional TBC. Key Words:Gas turbine, Vertical-crack induced thermal barrier coating, Thermal cycling, Bonding strength, Interface oxidation