Anisotropic thermal expansion effects in plasma-sprayed ZrO2-8 percent Y2O3 coatings

The thermal expansion properties of plasma-sprayed ZrO2-8-wt pct Y2O3 coatings, detached from the substrate, have been examined. Coatings were heat-treated in air or in argon. Anisotropic effects in the longitudinal (planar to the substrate surface) and transverse (perpendicular to the substrate surface) directions were measured and related to the coating structure. The thermal expansion coefficient of the coating is discussed in terms of the material's properties, such as the crack network and interlamellar boundary distribution. A precise model for the expansion behavior of coatings still needs attention, since no description of all of the contributing variables exists. A quantitative analysis of thermal properties of coatings will aid in future design and modeling of coating systems.