Chemical aspects of plasma spraying of zirconia-based thermal barrier coatings

Zirconia-based thermal barrier coatings (TBCs) of nominal chemical composition 8 wt.% Y2O3–ZrO2 and 25.5 wt.% CeO2–2.5 Y2O3–ZrO2 were prepared by atmospheric plasma spray and low-pressure plasma spray by selecting different deposition parameters. The surface chemical composition has been investigated by X-ray photoelectron spectroscopy in order to study the variation of surface chemical composition induced by the plasma-spraying process as a function of deposition parameters. The results reveal the occurrence of chemical–physical reactions such as stabilizing oxide depletion and enrichment, reduction to lower valence states, impurity segregation phenomena and the formation of new species. The chemical information was confirmed by differential thermal analysis measurements, which indicates that chemical aspects in plasma spraying are relevant and should be considered in designing reliable TBCs for maximum performance in aerospace applications.