Phase transformation during alternating aging at 473 K and at 773 K in the plasma-sprayed yttria stabilized zirconia coating

The phase transformation of plasma-sprayed 6 mass % yttria-stabilized zirconia coatings was investigated during alternating aging under two conditions, at 473 K in saturated steam pressure and at 773 K in air. Prior to the aging, the samples were annealed at 773 K and 1073 K in order to control stress relief. Selection of the annealing temperatures caused distinct differences in the phase transformation. After the first aging at 473 K, the monoclinic phase fraction in the coatings annealed at 773 K was found to be greater than that of the coatings annealed at 1073 K. In the coatings annealed at 773 K, the decrease of the monoclinic phase fraction was observed after aging at 473 K in each cycle, while the coatings annealed at 1073 K showed an increase of monoclinic phase fraction.