Graded EB-PVD Alumina-Zirconia Thermal Barrier Coatings-An Experimental Approach

Graded and homogeneous Al 2 O 3 -PYSZ thermal barrier coatings were processed by means of electron beam-physical vapor deposition in a dual source process. A compositional gradient was achieved by a suitable variation of deposition parameters. Both types of coatings show a dense and coarse columnar morphology with an internal multilayered structure which can be explained by a rotational effect. Coatings consist of nanocrystalline zirconia-rich and amorphous or nanocrystalline alumina-rich layers. Phase analysis reveals strongly broadened peaks of the tetragonal zirconia phase, but no alumina peaks. Annealing at 1100 °C in vacuum leads to formation of the crystalline α-Al 2 O 3 phase as well as zirconia grain growth while the multilayers dissappear. The grain growth can be described by a phenomenological growth law. The oxidation behavior of graded coatings was also investigated.