This study assesses the thermal stability of YSZ coatings produced from nanostructured feedstock by means of atmospheric and suspension plasma spraying. Free-standing YSZ coatings were isothermally treated for 24 h at different temperatures (1200-1600 °C) and at 1550 °C for 20 to 100 h. Afterwards, the coatings were examined to determine the effect of heating on phase composition, microstructure, morphology, and hardness. No evidence of tetragonal-monoclinic phase transformation was detected in the coatings that had been treated for 24 h, even at 1600 °C, but in coatings treated for different periods of time at 1550 °C, a phase transformation occurred after 40 h. Overall, the suspension plasma sprayed coating showed the greatest degree of change due to thermal aging.

High-purity nanocrystallized YSZ powders were used to manufacture thermal barrier coatings by air plasma spraying. After spraying, the coating samples were aged at temperatures of 1200, 1300, and 1400 °C. Coating samples made from ordinary YSZ powders were aged at the same temperatures. XRD analysis shows significant tetragonal-to-monoclinic phase transformation in the reference coatings after 100 h at 1400 °C in contrast to the phase stability exhibited by high-purity YSZ. The sintering behavior of the YSZ coatings was also examined along with the influence of MCrAlY oxidation.