Influence of bondcoat pre-treatment and surface topology on the lifetime of EB-PVD TBCs

In the present study two types of bondcoats (BC) were used, a NiCoCrAlY overlay coating produced by electron beam physical vapor deposition (EB-PVD) and a platinum aluminide diffusion coating (Ni,Pt)–Al. The coatings were deposited onto nickel-base IN100 and René142 substrates and were pre-treated in vacuum or Ar–H gas mixture prior to the deposition of an EB-PVD yttria partially stabilized zirconia top coat. The specimens were thermal cyclically tested in air at 1100 °C (50 min at 1100 °C/10 min forced air cooling). The microstructures of the thermally grown oxide (TGO) layers prior and after testing were examined by scanning electron microscopy and electron energy dispersive spectroscopy. Heat-treatment in Ar–H significantly improved the lifetime of the thermal barrier coatings (TBC) system with IN100+PtAl BC, whereas reduced lifetimes were found on IN100+NiCoCrAlY BC and René142+PtAl. High Y-contents of the NiCoCrAlY BC significantly reduced TBC lifetimes. Furthermore, the results for IN100+PtAl and René142+PtAl demonstrated that early TBC failure was associated with high TGO surface roughness of the metal/oxide interface, indicating that surface roughness has a significant effect on TBC system performance.