Cyclic Hot Corrosion of Thermal Barrier Coatings and Overlay Coatings

The influence, and interdependence, of water vapor and Na₂SO₄–50 mol% NaCl on the oxidation of a NiCoCrAlY coating and a thermal barrier coating (TBC) were studied at 750 °C. Water vapor was found to have a negligible effect on oxide composition, but influenced the oxide morphology on the NiCoCrAlY coating. Na₂SO₄–50 mol% NaCl deposits on the coatings influenced oxide composition, most notably by the promotion of a Y rich phase. The effect of Na₂SO₄–50 mol% NaCl deposits was also evident for the TBC coated specimen, where the formed metal/ceramic interface oxide was affected by salt reaching the interface by penetration of the zirconia TBC.