MICROSTRUCTURE OF YTTRIA-STABILIZED ZIRCONIA-HAFNIA PLASMA-SPRAYED THERMAL BARRIER COATINGS

Hafnia is an attractive candidate to build reliable and durable therma l barrier systems, due to its similarity to zirconia and its elevated structural transformation temperatures. We report here structural inve stigations of various plasma sprayed coatings composed of ZrO2 + x mol e % HfO2 (x = 0, 25, 50 and 100), partially stabilized by 4.53 mole % yttria. X-Ray diffraction studies and TEM investigations show that, a metastable, non transformable, high yttrium content, t' phase is the o nly phase observed on the as-sprayed samples. Such results has not bee n yet related in the literature.