Cyclic behavior of EB-PVD thermal barrier coating systems with modified bond coats

The lifetime of thermal barrier coating (TBC) systems depends on substrate, bond coat, thermally grown oxide (TGO), and ceramic top coat. In the present paper NiPtAl bond coats as well as NiCoCrAlY(X) deposited by LPPS and EB-PVD (electron-beam physical vapour deposition) underneath conventional EB-PVD yttria stabilized zirconia top coats were investigated on three different substrate alloys. Several bond coat treatments such as polishing, annealing in vacuum, and grit blasting were employed in order to study effects on TBC life, and particularly the underlying mechanisms of TGO formation. Samples were thermally cycled at 1100 °C and partly at 1150 °C. Spallation of the TBCs is mainly correlated with TGO formation that is influenced by bond coat type and pre-treatment. The longest lifetimes were achieved on a novel Hf-doped EB-PVD NiCoCrAlY-X bond coat owing to a differing TGO formation and failure mechanism. Activation energies derived from lifetimes and test temperatures were calculated to identify key failure mechanisms within these complex coating systems.