Influence of water vapor on the high temperature oxidation behavior of thermal barrier coatings

The oxidation of thermal barrier coating (TBC) specimens consisting of nickel-base superalloy, low-pressure plasma sprayed Ni-28Cr-6Al-0.4Y (wt.%) bond coatings and air plasma-sprayed 7.5 wt.% yttria stabilized zirconia top coatings was studied at 1050 degreesC in flows of O-2, and mixture of O-2 and 5%H2O under atmospheric pressure. The TBC exhibits very low oxidation rate at 1050 degreesC in pure O-2 and the oxidation kinetics accords with parabolic law. The oxidation kinetics of TBC obeys almost linear law after long exposure times in the presence of 5% water vapor. Oxide formed along the bond coat and top coat interface after oxidation at 1050 degreesC in pure O-2 consisted of Al2O3, whereas interfacial scales formed after oxidation at 1050 degreesC in a mixture of O-2 and 5%H2O were mainly composed of Ni(Al,Cr)(2)O-4, 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. (C) 2002 Elsevier Science B.V. All rights reserved.