Thermal properties of ceria and yttria partially stabilized zirconia thermal barrier coatings

Abstract

Coatings consisting of zirconia alloyed with 12, 15, 20 and 25 wt.% ceria or 4, 6, 8, 10 and 12 wt.% yttria were prepared using the plasma spray process. For each of these coatings measurements were made of thermal expansion parallel to the substrate and of thermal conductivity perpendicular to the substrate. These results are discussed in conjunction with the phase stability of the specimens, as determined by X-ray diffraction. Coatings containing 25 wt.% ceria or greater than 8 wt.% yttria were found to have stable thermal properties. Coatings containing less of these additions exhibited a thermal expansion hysterisis which was most pronounced at the lowest concentrations. The temperature at which the hysterisis occured was found to reduce with increasing additions of alloying agent. This behaviour was also detected for ZrO 2−CeO 2 as a change in thermal diffusivity during thermal cycling and is attributed to a reversible tetragonal-monoclinic transformation.