Thermal barrier coatings (TBC’s) are used to protect metallic components form extreme conditions like those encountered in turbine engines (Figure 1). TBC’s serve two purposes in these applications. They prevent the oxidation of the superalloy and create a thermal gradient between the surface of the metal and the working fluid of the engine. To fulfill these two functions, the TBC is made up of two layers (Figure 2). A metallic bond coat (typically a Ni-Cr-Al-Y alloy (NiCrAlY)) is applied to the base superalloy to protect it from oxidation, and then a ceramic top coat (typically a ZrO2-Y2O3 mixture referred to as Yttria-stabilized Zirconia (YSZ)) is deposited on top to thermally insulate the metallic components from high service temperatures (approaching 1200 °C).

TBC’s fail when portions of the coating spall off to expose the part’s surface. Spallation occurs because the ceramic top coat goes into compression when the part is cooled from the operating temperature and buckles when flaws at the metal/ceramic interface reach a critical size (on the order of a few millimeters). In most TBC’s, flaws exist already exist in the as-deposited coating. In this research, the growth of these flaws under the influence of thermal residual stresses is investigated.