Characterization of bond coat in a thermal barrier coated superalloy used in combustor liners of aero engines

This paper deals with characterization of a thermal barrier coated (TBC) Supeni 263 super alloy, mostly employed for manufacturing combustion chamber of aero turbines, with respect to microstructure, residual stress, hardness and with special emphasis in establishing the ductile to brittle transition temperature (DBTT) of the bond coat by using acoustic emission technique during room temperature and high temperature tensile tests. Results reveal that the residual stress was tensile in nature in the TBC layer and compressive in the bond coat as well as in the substrate. The DBTT of this bond coat is around 650 °C, which is in close proximity to the value reported in literature for CoCrAlY type of bond coat. Finite element technique used for analyzing the equivalent stresses in the bond coat, at a particular load within the elastic limit of the composite specimens, revealed highest order of equivalent stress at 800 °C as the bond coat is ductile above 650 °C. Delamination of the bond coat and spallation of the TBC were evident at high stresses during high temperature (800 °C) fatigue.