Evaluation of CaO-CeO2-partially stabilized zirconia thermal barrier coatings

Plasma sprayable powders were prepared from ZrO2-CaO-CeO2 system using an o rganic binder and coated onto stainless steel substrates previously coated by a bond coat (Ni 22Cr 20Al 1.0Y) using plasma spraying. The coatings exhi bited good thermal barrier characteristics and excellent resistance to ther mal shock at 1000 degrees C under simulated laboratory conditions (90 half hour cycles without failure) and at 1200 degrees C under accelerated burner rig test conditions (500 2 min cycles without failure). No destabilization of cubic/tetragonal ZrO2 phase fraction occured either during the long hou rs (45 h cumulative) or the large number of thermal shock tests. Growth of a distinct SiO2 rich region within the ceramic was observed in the specimen s thermal shock cycled at 1000 degrees C apart from mild oxidation of the b ond coat. The specimens tested at 1200 degrees C had a glassy appearance on the top surface and exhibited severe oxidation of the bond coat at the cer amic-bond coat interface. The glassy appearance of the surface is due to th e formation of a liquid silicate layer attributable to the impurity phase p resent in commercial grade ZrO2 powder. These observations are supported by SEM analysis and quantitative EDAX data. (C) 1999 Elsevier Science Limited and Techna S.r.l. All rights reserved.