Abstract
Recently, thermal barrier coatings (TBC) have been used in advanced gas turbine plants to improve the durability and performance of turbine blades. Usually, TBCs consist of an inner layer of metallic bond coating (MCrAlY) and an outer layer of ceramic top coating. According to several studies, the failure of such coatings is induced by thermal stress due to the formation of thermally grown oxide (TGO) at the interface between the TBC and MCrAlY. Therefore, it is important to investigate the oxidation behavior of the interface at high temperatures. In this work, the TGO, which forms at the interface, is characterized in detail. Moreover, for the purpose of understanding oxide formation at the interface, the oxidation behavior of specimens with and without TBC are compared. The TBC specimens are thermally aged at high temperature to simulate the surface temperature of the first rotating blades of 1500deg.C class gas turbine plants. After aging, TGO formed at the interface. The TGO formed is observed to consist of two different oxide layers. The thickness of the two oxide layers increases with the aging time. As a result of a comparison between the specimens with and without TBC, the TGO thickness of the specimen with TBC is observed to be thicker than for the specimen without TBC. These specimens exhibited different oxidation behaviors, which are caused by specimen dependent preferential growth of one of the oxide layers for the specimen with TBC.
