Influence of water vapor on the isothermal oxidation behavior of thermal barrier coatings

The oxidation of specimens with thermal barrier coating (TBC) consisted of nickel-base superalloy, low-pressure plasma sprayed Ni-28Cr-6Al-0.4Y (wt pct) bond coating and electron beam physical vapor deposited 7.5 wt pct yttria stabilized zirconia (YSZ) top coating was studied at 1050°C respectively in the flow of O₂ and the mixture of O₂ and 5%H₂O under atmospheric pressure. The thermal barrier coating has relatively low oxidation rate at 1050°C in pure O₂. The oxidation rate of thermal barrier coating in the atmosphere of O₂ is increased. The oxidation kinetics obeys almost a linear law after a long exposure time in the presence of 5% water vapor. The oxide formed along the interface between bond coat and top coat after the oxidation at 1050°C in pure O₂ consisted of Al₂O₃, whereas interfacial scales formed after the oxidation at 1050°C in a mixture of O₂ and 5%H₂O were mainly composed of Ni(Al, Cr) ₂O₄, NiO 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 in the oxides.