ELECTROPHORETIC DEPOSITION OF ENVIRONMENTAL BARRIER OVERLAY COATINGS FOR YTTRIA-STABILIZED ZIRCONIA THERMAL BARRIER COATINGS

摘要

Thermal barrier coatings (TBCs) are increasingly susceptible to environmental degradation due to molten deposits of fuel impurities and air ingested sand. At elevated temperature, these deposits adhere, melt and degrade the TBCs via repeated freeze-thaw action and, to a certain extent, direct chemical reaction with TBC constituents. In order to protect TBCs from such melt ingression, a thin, dense and continuous environmental barrier overlay coating can be applied on the surface of TBCs. In this study, dense, continuous and crack-free overlay coatings of YSZ, Al_2O_3 and MgO were fabricated by electrophoretic deposition (EPD) on air-plasma sprayed (APS) YSZ. APS YSZ specimens of 300 μm thickness were prepared from 8YSZ powders on graphite substrates. A stable colloidal suspension of YSZ, Al_2O_3 and MgO powders in an organic solvent mixture of acetone and ethanol with Iodine additive was used for EPD. At a controlled applied DC voltage with deposition time within minutes, a crack-free green compact can be obtained. After drying and controlled sintering at high temperature, thin, dense, crack-free overlay coatings of controlled thickness on free-standing YSZ were produced. The coatings were characterized by x-ray diffraction and scanning electron microscopy. The degradation resistance of overlay coatings fabricated by EPD and sintering for YSZ TBCs against melt ingression of CMAS and V_2O_5 is highlighted.