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IMPROVING THE CORROSIVE DURABILITY OF THERMAL BARRIER COATINGS
Conventional yttria stabilized zirconia (7YSZ) thermal barrier coatings
(TBCs) that are currently used in gas turbine engines undergo hot
corrosion by sulfate/vanadate deposits commonly found in marine
environments. These deposits destabilize the zirconia by reacting
with and leaching out yttria from the zirconia structure, eventually
causing a destructive monoclinic phase transformation that ultimately
results in the TBC detaching from the underlying alloy component.
In response to the current failures of TBCs, an investigation of
the effectiveness of stabilizing the zirconia structure by co-doping
with yttrium and tantalum is being investigated. Through reverse
co-precipitation with precursors, three baseline samples of yttria
stabilized zirconia (YSZ), and two samples of YSZ co-doped with
tantalum were made. The samples were then pyrolized to obtain an
oxide in powder form, pressed into pellets, coated with a Na2SO4-30mole%NaVO3
salt as a corrodent to simulate the sulfate/vanadate deposits, and
then tested at 900oC in air. Analysis of changes in microstructure
and composition were done with the use of X-Ray Diffraction, scanning
electron microscopy, electron dispersive spectroscopy, and transmission
electron microscopy in order to compare the relative stability of
the compositions and their resistance to hot corrosion.
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