Electron beam-physical vapor deposition - thermal barrier coatings on laser drilled surfaces for transpiration cooling

In this paper the deposition behavior of zirconia on laser drilled surfaces is reported. The samples were prepared with laser drilled holes (diameter 200 μm) with tilting angles of 0°, 15°, 30°, 45° and 56°. As substrate material, VPS-MCrAlY-coated nickel-based superalloy was used. The zirconia thermal barrier coatings were deposited by the electron beam-physical vapor deposition (EB-PVD) technique. The extent by which the tilted holes were closed by the deposition process were examined. With increasing tilting angle the holes were closed during the deposition of the thermal barrier coating with decreasing of coating thickness. In additional experiments, a gas (argon) flowed through the holes during the deposition process. Due to the lower temperature of the surrounding area to the holes caused by the cold gas stream, the holes were closed faster by the ceramic vapor compared with the deposition without gas flow. Another effect of the gas flow was the formation of non-stoichiometric zirconia near the holes which was evident by the darker color.