Sintering and creep behavior of plasma-sprayed zirconia- and hafnia-based thermal barrier coatings

The sintering and creep of plasma-sprayed ceramic thermal barrier coatings under high temperature conditions are complex phenomena. Changes in thermomechanical and thermophysical properties and in the stress response of these coating systems as a result of the sintering and creep processes are detrimental to coating thermal fatigue resistance and performance. In this paper, the sintering characteristics of ZrO2-8wt%Y2O3, ZrO2-25wt%CeO2-2.5wt%Y2O3, ZrO2-6w%NiO-9wt%Y2O3, ZrO2-6wt%Sc2O3-2wt%Y2O3 and HfO2-27wt%Y2O3 coating materials were investigated using dilatometry. It was found that the KfO(2)-Y2O3 and baseline ZrO2-Y2O3 exhibited the best sintering resistance, while the NiO-doped ZrO2-Y2O3 showed the highest shrinkage strain rates during the tests. Higher shrinkage strain rates of the coating materials were also observed when the specimens were tested in Ar+5%H-2 as compared to in air. This phenomenon was attributed to an enhanced metal cation interstitial diffusion mechanism under the reducing conditions. It is proposed that increased chemical stability of coating materials will improve the material sintering resistance. (C) 1998 Elsevier Science S.A. All rights reserved.