Single-step fabrication of nanolamellar structured oxide ceramic coatings by metal-organic chemical vapor deposition

Oxide ceramic coatings in the system Y2O3-Al2O3-ZrO2 were fabricated in laboratory scale by using a MOCVD unit. A hot wall reactor was used along with different precursor feeding systems. Most experiments were carried out by using powder flash evaporation including a screw feeder for precursor powder delivery. For comparison, further samples were fabricated by using band flash evaporation and continuous evaporation from a crucible. Oxygen was used in all cases as reactant gas. Aluminium-tris-2,4-pentanedione (Al(acac)3), yttrium-tris-2,2,6,6-tetramethyl-3,5-heptanedione (Y(thd)3) and zirconium-tetrakis-2,2,6,6-tetramethyl-3,5-heptanedione (Zr(thd)4) were applied as metal-organic precursors because of their similar vaporization behaviour under the given conditions. The coating stoichiometry was varied from pure alumina to complex ternary compositions in the system Y2O3-Al2O3-ZrO2. Both kinds of ternary coatings fabricated by using flash evaporation methods show a nanolamellar microstructure in the as deposited state. Heat treating experiments at 1200 degrees C for up to 5 days enhance the lamellar character of the coating deposited by using powder flash evaporation. The lamellar microstructure is due to alternating YSZ enriched layers and YAG enriched layers in this state. However, the coating fabricated by using band flash evaporation shows a dense interpenetrating network of YSZ and YAG after heat treating instead of a lamellar microstructure observed in the as deposited state.