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

Hafnia is an attractive candidate to build reliable and durable thermal barrier systems, due to its similarity to zirconia and its elevated structural transformation temperatures. We report here structural investigations of various plasma sprayed coatings composed of ZrO2 + x mole % 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 only phase observed on the as-sprayed samples. Such results has not been yet related in the literature.