Electrophoretic deposition of yttria-stabilized zirconia for application in thermal barrier coatings

Access to files

•   FULL-TEXT.PDF (pdf)

Abstract

Electrophoretic deposition (EPD) has been used to produce the yttria-stabilizedzirconia (YSZ) coatings on metal substrates. Sintering of YSZ with and withoutdoping has been carried out at 1150 °C for 2hrs. The properties of these coatingshave been examined in light of thermal barrier applications.For EPD, the green density increases with an initial increase in the HCl concentrationand the EPD time. This suggests that particle packing was influenced by a timedependent re-arrangement, in addition to the initial suspension dispersion state. Thegreen density peaks at a electrical conductivity of around 10×10-4 S/m achieved byan 0.5 mM HCl addition for the 20 g/l suspensions with the EPD time of around 8 ~10 minute. For sintered coatings, the HCl concentration had a marked effect on theneck size to grain size ratio of the 8 mol% yttria-stabilized zirconia (8YSZ) coatings.The presence of ZrCl4 and ZrOCl2, and a high concentration of oxygen vacancies atthe grain boundaries are believed to promote neck growth in the early stage ofsintering at 1150 °C.During sintering of 3 mol% and 8 mol% yttria-stabilized zirconia (3YSZ and 8YSZ)at 1150 ºC for 2hrs, the densification rate substantially increased with a small amountof Fe2O3 addition (0.5 mol%) to the 3YSZ/8YSZ deposits. A more pronounced graingrowth was present in the Fe2O3 doped 8YSZ deposits. The increased Zr4+ diffusioncoefficient is mainly responsible to the rapid densification rate of the Fe2O3 doped3YSZ/8YSZ deposits. A small grain growth observed in the Fe2O3 doped 3YSZdeposits is attributed to the Fe3+ segregation at grain boundary. A small amount ofCeO2 doping was found to substantially inhibited densification rate of the doped3YSZ deposits with a minor grain growth.Fe2O3 doping reduced the thermal conductivities of 3YSZ/8YSZ. It is found thatRayleigh-type phonon scattering due to the mass difference alone is inadequate toexplain the thermal conductivity of Fe2O3 doped YSZ systems. The lattice straineffects due to the ionic radius difference could more effectively reduce thermalconductivity of the Fe2O3-doped 3YSZ. A decrease in the growth rate of the TGOscale with the increasing Fe2O3 additions was observed for the oxidized FeCrAlYmetal substrates with the Fe2O3-doped 3YSZ coating, which was found to beattributed to the early formation of the stable and dense α-Al2O3 phase due to thepresence of Fe3+ ions.

Keyword(s)

electrophoretic deposition (EPD); thermal barrier coatings (TBCs); yttria stabilized zirconia (YSZ)

Bibliographic metadata

Institutional metadata

Record metadata