Phase transformation behavior in air plasma sprayed yttria stabilized zirconia coating

Yttria stabilized zirconia has been widely applied as thermal barrier coatings for high temperature heat insulation. However, prepared by air plasma spraying, YSZ TBCs suffer from severe phase separation of metastable T′ phase into thermodynamic equilibrium T and C phases, which consequently leading to cracking and delamination of the coatings. In the present research, the kinetics of T′→T + C reaction was experimentally investigated. By AVARAMI equation fitting, the reaction order and apparent activation energy were obtained to be 0.7-1.4 and 515 ± 32 kJ/mol, indicating a complex crystallization and grain growth controlling mechanism of the phase degradation process. Combination effect of temperature and time on the reaction was normalized by Hollomon-Jaffe Parameter. The results provide a reasonable prediction of the phase evolution, as well as the related thermal and mechanical properties of TBCs during long term application.