Monoclinic zirconia distributions in plasma-sprayed thermal barrier coatings

Phase composition in an air plasma-sprayed Y2O3-stabilized ZrO2 (YSZ) top c oating of a thermal barrier coating (TBC) system was characterized. Both th e bulk phase content and localized pockets of monoclinic zirconia were meas ured with Raman spectroscopy, The starting powder consisted of similar to 1 5 vol.% monoclinic zirconia, which decreased to similar to 2 vol.% in the a s-sprayed coating. Monoclinic zirconia was concentrated in porous pockets t hat were evenly distributed throughout the TBC. The pockets resulted from t he presence of unmelted granules in the starting powder. The potential effe ct of the distributed monoclinic pockets on TBC performance is discussed.