Microanalysis on the oxidation and sulfate attack of partially stabilized zirconia thermal barrier coating

Journal article, 2001

This aim of this investigation is to study the effect of the presence of Na2SO4 deposits and water vapor on the oxidation of an air plasma-sprayed TBC composed of a partially stabilized ZrO2 top coat with an underlying NiCoCrAlY bond coat. XRD and SEM/EDX were used to analyze the changes in the coatings after oxidation at 1000degreesC for 72 hours in dry or humidified (containing 50% H2O) O-2 atmosphere, with or without Na2SO4 deposited on the top coat. When oxidized in oxygen, bond coat oxide regions, consisting of almost pure aluminum oxide, were formed at the top coat / bond coat and bond coat / substrate interfaces and in the bond coat around the splat lines. When water vapor was present, the top coat / bond coat interface oxide was marginally thicker and included small regions with more chromium, cobalt and nickel. The addition of the salt deposits resulted in some destabilization in the outermost regions of the top coat. The salt deposits also caused the formation of thicker oxide comprising two regions, though this formation was observed only at the top coat / bond coat interface. The first type was a thin inner (i.e. bordering the bond coat) oxide that was mostly aluminum oxide. The other was a much thicker oxide containing higher levels of chromium, cobalt and nickel along with aluminum. In this oxide region, the aluminum level was higher when the chromium level was lower and vice versa.