Abstract
The oxidation of a low-pressure plasma-sprayed (LPPS) NiCrAlY coating on a nickel-base superalloy was studied at 1050 °C in flows of O2, and mixture of O2 and 5% H2O under atmospheric pressure. Water vapor has an obvious effect on the cyclic oxidation of the NiCrAlY coating. There is more decrease in weight gain when exposure to O2 is replaced by exposure to O2 + 5% H2O. The oxide formed on the LPPS NiCrAlY coating after cyclic oxidation in pure oxygen is composed mainly of Cr2O3, and a thin Al2O3-rich layer is formed at the interface between the Cr2O3-rich layer and the coating. The oxide formed on the LPPS NiCrAlY coating after cyclic oxidation in a mixture of O2 + H2O is composed of NiCr2O4, NiO and Cr2O3. The effect of water vapor on the oxidation of the NiCrAlY coating may be attributed to an increase in Ni and Cr cation transport, stress-corrosion cracking of Al2O3 and moisture-enhanced volatility of the Cr2O3 scale.
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