Influence of water vapor on the isothermal oxidation behavior of low pressure plasma sprayed NiCrAlY coating at high temperature

The oxidation of low pressure plasma sprayed (LPPS) NiCrAlY coatings on nickel base superalloy were studied at 1050°C in flows of O₂, and mixture of O₂ and 5% H₂O under atmospheric pressure. NiCrAlY coating exhibits a very low oxidation rate at 1050°C in pure O₂ and the oxidation kinetics accords with a parabolic law. The oxidation kinetics of NiCrAlY coating obeys almost a linear law after long exposure times in the presence of 5% water vapor. The oxide formed on the surface of LPPS NiCrAlY coating after oxidation at 1050°C in pure O₂ consisted of Al₂O₃, whereas the oxide formed on the surface of LPPS NiCrAlY coating after oxidation at 1050°C in a mixture of O₂ and 5% H₂O is mainly composed of NiCr₂O₄, NiO, Cr₂O₃ and Al₂O₃. It is suggested that the effect of water vapor on the oxidation of the NiCrAlY coating may be attributed to the increase in Ni and Cr ions transport.