Evaluation of CaO–CeO 2–partially stabilized zirconia thermal barrier coatings

Abstract

Plasma sprayable powders were prepared from ZrO 2–CaO–CeO 2 system using an organic binder and coated onto stainless steel substrates previously coated by a bond coat (Ni 22Cr 20Al 1.0Y) using plasma spraying. The coatings exhibited good thermal barrier characteristics and excellent resistance to thermal shock at 1000°C under simulated laboratory conditions (90 half hour cycles without failure) and at 1200°C under accelerated burner rig test conditions (500 2 min cycles without failure). No destabilization of cubic/tetragonal ZrO 2 phase fraction occured either during the long hours (45 h cumulative) or the large number of thermal shock tests. Growth of a distinct SiO 2 rich region within the ceramic was observed in the specimens thermal shock cycled at 1000°C apart from mild oxidation of the bond coat. The specimens tested at 1200°C had a glassy appearance on the top surface and exhibited severe oxidation of the bond coat at the ceramic–bond coat interface. The glassy appearance of the surface is due to the formation of a liquid silicate layer attributable to the impurity phase present in commercial grade ZrO 2 powder. These observations are supported by SEM analysis and quantitative EDAX data.