As-deposited mixed zone in thermally grown oxide beneath a thermal barrier coating

Gas turbine designers are increasingly using electron-beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBC) to meet the challenge of higher efficiency gas turbine engine requirements. A key feature for expanding the use of TBCs is increased spallation life and reduced spallation life variability. Such a coating system comprises a substrate (Ni-based single crystal alloy), a bond coat (diffusion aluminide or MCrAlY), a ceramic (7 wt.% yttria stabilized zirconia), and a thin thermally grown oxide (TGO) between the bond coat and the ceramic. The TGO is intended to be α-alumina, but evidence reported by other researchers suggests that in some cases the as-deposited TGO may not be entirely α-alumina. The thin nature of the TGO in as-deposited TBCs (