Advanced Thermal Barrier Coating

Abstract : The primary research objective of this work was to develop a novel thermal barrier coating (TEC) system by depositing a high quality alpha alumina sublayer on the metallic bond-coat, prior to the deposition of the yttria stabilized zirconia (YSZ) coating. A patented filtered cathodic arc deposition equipment was used to deposit an alpha alumina layer on a superalloy that was plasma-spray coated with a NiCoCrAlY bond-coat. The filtered arc coating process allows droplet-free deposition 0 coatings. Also, this process provides high ionization (>90%) compared with the standard physical vapor deposition processes (<20%), thereby providing excellent bonding between the coating and the substrate. Using this approach, 0.5-0.6 micron thick alpha alumina coatings were deposited on metallic substrate at 925 deg C. Oxidation tests reveal that further improvements are necessary for the system to perform better than state-of-the-art TBCs. The performance was impaired by microstructural instability and surface rumpling of the bond-coat, which caused failure of the alumina layer at a number of locations.