Some Problems on Evaluating Elastic Modulus of APSed Ceramic Top Coat for TBCs by Indentation Method

Abstract

Elastic modulus of air plasma sprayed (APSed) YSZ (; ZrO2 stabilized by 8 wt. pct. Y2O3) top coat specimen, which is frequently used for thermal barrier coating (TBC) system for advanced gas turbines, was measured by employing the macro-, micro-, and nano-indentation methods. The elastic modulus was measured, following the Oliver-Pharr method. It was shown that the elastic modulus of the YSZ, as well as the microstructure, was significantly influenced by the spraying conditions employed. Especially the size of ceramic powders used was found to have the most pronounced effect. It was also shown that the elastic modulus revealed significant size effect: that is, there were significant differences in elastic modulus measured by the instruments on the macro-, micro-, and nano-levels. This size effect was discussed, correlating with some relating phenomena: crackings, sink-in, pile-up and spalling; as well as with the characteristic microstructures of the sprayed top coat.