Investigation of Microstructural Properties and Isothermal Oxidation Behavior of Thermal Barrier Coatings (TBCs) with MCrAlY Bond Coat

Abstract

Thermal barrier coatings (TBCs) are advanced protective coatings operating at elevated temperatures used to protect the fixed and movable parts of aero-engines and industrial gas turbine engines from environmental adverse effects. In the TBC system, the substrate material, metallic bonding and ceramic top coat materials used to protect against the major damage formation mechanisms such as oxidation and corrosion that may occur during service are the main elements that determine the life of the TBC system under usage conditions. In this study, NiCrAlY containing a metallic bonding coat and yttria stabilized zirconia (YSZ) coating were produced using atmospheric plasma spray (APS) coating method. The TBC system produced was subjected to isothermal oxidation tests at 1150 degrees C and at 5, 25 and 50 hours of time period. Scanning electron microscope (SEM) analysis was conducted before and after high temperature furnace tests in order to determine microstructural changes. The changes in the characteristics of the oxide structures formed in the metallic bonding and ceramic top coat interface structure based on time during the high temperature process have been studied and evaluated in detail. It has been observed that depending on the oxidation process, thermally grown oxide layer (TGO) structure is formed at the interface of the metallic bonding and ceramic top coat, and this layer, dependent on the increasing oxidation process, grows parabolically. It has been determined that the content and growth behavior of the TGO layer varies depending on the alloying elements in the bonding coat, except oxygen diffused from the surface to the interface.